Technical Help

For over 25 years, Parts Express has been 'Your #1 Source for Audio, Video and Speaker Building Components'. We collected customer service related questions from other customers like you, and have assembled them here. If you need additional help, or have any questions, you can contact us via e-mail at tech@parts-express.com .

Speaker Building

What does a crossover do?

What is the difference in a passive and active crossover?

What is a 2-way crossover?

What is a 3-way crossover?

What are the benefits of a passive crossover?

Do you have an example of a 2-way crossover design?

How do capacitors work?

How do coils work?

How do I replace the foam surround on my speaker?

How do I build a crossover?

How do I build my own speakers?

How do I attach carpet to a speaker box?

How do I attach a grill to a speaker cabinet?

Do you carry design programs?

What does a crossover do?

A crossover is a device that separates or “filters” the audible bandwidth of frequencies down to limited bandwidths, and routes them to the appropriate component of the sound system. There are two main types of crossovers: active and passive. Crossovers can take many different forms, from very basic (a single component) to very complex.

Browse our Crossover Components Selection

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What is the difference in a passive and active crossover?

Passive crossovers are the most common type of crossover, and employ “passive” devices such as capacitors, coils, and resistors to limit the bandwidth of the amplified audio signal before it is applied to the associated speaker in the cabinet. Passive crossovers are most commonly found in full range speaker cabinets, and therefore work with the audio signal after it has been amplified to a level sufficient to drive a loudspeaker. Virtually all home audio speakers use passive crossovers. Many full range sound reinforcement speaker systems contain them as well. They often have alternate inputs for use with active crossovers to make them more versatile.

Active crossovers are most commonly found in sound reinforcement systems such as a band, DJ, or concert venue would use. These are an electronic (active) device that works with the audio signal before it is amplified.  Its outputs are then routed to the appropriate amplifier(s) that then drive just those speakers (woofers, midranges, etc.) that are to reproduce the specific bandwidth of frequencies applied. Multiple amplifiers are required to create a “full range” speaker system when using active crossovers.  These are commonly referred to as “bi-amped” and “tri-amped” systems.

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What is a 2-way crossover?

In a 2-way speaker system, a woofer(s) is used to reproduce the lower frequencies, a tweeter to produce higher frequencies. The crossover therefore has two filters and is therefore called a 2-way crossover. The crossover frequency is the point that the woofer does not receive frequencies above, or the tweeter frequencies below. The woofer's filter is called a 'low pass' because it only allows frequencies at and below the crossover frequency to pass to the woofer. It blocks higher frequencies from reaching the woofer. The tweeter’s filter is called a 'high pass', passing frequencies higher than the crossover frequency, and blocking those below.

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What is a 3-way crossover?

A 3-way crossover generally has two more filters than a 2-way to accommodate a midrange speaker.  The two filters limit how high and how low the midrange plays, and allows it to blend with the woofer and tweeter.

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What are the benefits of a passive crossover?

  • Somewhat an over-simplification, but for a given frequency, there is only one speaker in the cabinet reproducing it. If the woofer and tweeter are both 8-ohm impedance, the amplifier therefore always “sees” an overall 8-ohm load.  
  • Without the crossover, the woofer and tweeter would reproduce some of the same frequencies. This would increase the apparent volume level and drop the impedance within this range of frequencies. This is very undesirable in a speaker system. 
  • Tweeters are easily damaged by low frequencies that they are not designed to reproduce. 
  • No single speaker currently available can, by itself in the cabinet, reproduce the total bandwidth of audible frequencies with the fidelity and (low) distortion level of a 2 or 3-way speaker system using a passive crossover.

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Do you have an example of a 2-way crossover design?

We have an entire walkthrough, including video, located in our resources section.

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How do capacitors work?

There is an extensive walkthrough and explanation on capacitors located in our resources section

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How do coils work?

The terms inductor , coil , and choke are synonymous. A coil is a winding of insulated wire wrapped around a core . The unit of measure for Inductance is the Henry ; the symbol is L . Inductors used in the audio range of frequencies are in the lower millihenry (thousandths of a Henry, mH) value. Continue reading...

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How do I replace the foam surround on my speaker?

Learn how to replace the foam surround.

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How do I build a crossover?

Often, one of the most daunting tasks that the beginning speaker-builder faces is building a crossover from scratch. It is easy enough to look at and understand a printed crossover schematic, but it is an altogether different matter to actually build it out of real components. Fortunately, the experts at Parts Express have got you covered. Continue reading for detailed instructions, including a video!

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How do I build my own speakers?

Such audio systems are referred to as High Impedance, Constant Voltage, or 70V systems. They are intended specifically for audio systems where many speakers are needed, speaker wire runs are long, and high fidelity for music reproduction is not a main concern.

 

 

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How do I attach carpet to a speaker box?

Carpeting is attached to speaker boxes or cabinets using a spray adhesive intended for such an application. Before purchasing carpet, calculate the surface area of the cabinet. Add about 1/3 more to that area so that you have plenty of carpet, and won't be left 'patching' uncovered areas.
 
Once a piece of carpet has been cut to size, spray a light coat of adhesive to one side and let it begin to cure (dry). Spray a meduim coat of adhesive onto the cabinet, and allow it to begin to cure as well. Apply the carpet, and ensure that it does not slide or move until the adhesive had cured sufficiently to hold it in place. Be sure the carpet is positioned properlyl and all wrinkles and slack are worked out before leaving it to dry. Do not attempt to apply more carpet until it is dry. 

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How do I attach a grill to a speaker cabinet?

 There are three common methods for attaching a grill to a speaker cabinet.
 
'Velcro' or hook and loop, is a common and convenient method. Hook and loop can be purchased with a peel-and-stick adhesive backing. Apply one side of the hook and look to the back of the grill, one at each corner or where appropriate. Then press the mating side onto it. Peel the backing from the mating side, carefully position the frame over the cabinet front, then press into place. The hook and loop will remain attached to the grill and the cabinet, allowing for easy removal and installation.
 
Plastic ball and socket-type fasteners are called 'grill guides'. These are mounted to the grill frame and cabinet by drilling holes for the guide halves and securing them with an adhesive such as epoxy. Using grill guides does require accurate location of the holes for the guide halves. The guides are sometimes known to break as well.
 
Small, round neodymium magnets are a popular method for attaching grills. The magnets must be able to come into contact with each other to securely hold the grill frame, so positioning and mounting depth of the magnets are critical.

Do you carry design programs?

Yes. We have computer modeling programs for designing speaker cabinets and passive crossover networks. The program for cabinet designs is for designing a cabinet to work with a specific woofer. The woofer's Thiele/Small parameters must be available for the program to work. It can do sealed, ported, and band pass enclosures.
 
The program for passive crossovers will do 2-way and 3-way systems, from 1st Order to 4th Order, in several alignments such as Butterworth, Linkwitz/Riley, All-pass, and Constant Power. This program predicts or models the net frequency response of a speaker system using the woofer, tweeter, and midrange speaker's parameters.
 

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Speakers

What's the difference between a woofer and a subwoofer?

What does a subwoofer do?

How is a subwoofer amplifier's low pass active filter adjusted?

What is the difference between an active and a passive subwoofer?

Why is adjusting the frequency that comes out of the subwoofer so important?

How do I match a speaker replacement to my current system?

Do you recone speakers?

How do I select the right speaker surround repair kit for my speaker?

How do I measure my speaker?

What is speaker phase? Is maintaining speaker polarity important?

What's the difference between a woofer and a subwoofer?

These terms have become almost interchangeable, and there is definitely a gray area between the two. The difference can be in the woofer itself, or how the woofer is being used.

A raw speaker or 'driver' that we call a subwoofer generally has a limited frequency response range, often not extending above about 400 Hz. A standard 'woofer' can have frequency response easily reaching 2500 Hz or higher. This upper limit is a function of electrical and mechanical characteristics; often the large voice coil inductances on high-excursion subwoofers limit their high-frequency capabilities.

It is a matter of compromise in the design of the woofer.  Trying to achieve good high frequency performance generally will cause poor low frequency and power handling abilities while producing a powerful subwoofer with ultra-low frequency abilities and high power handling will not be able to play well at higher frequencies. However, if a wider-range woofer is used only below 80 Hz or so it could be called a subwoofer due to how it is being implemented.

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What does a subwoofer do?

A subwoofer is used to reproduce the lowest frequencies that other speakers in the system can't reach at full volume. In the most general application, the subwoofer will work with a pair of smaller speakers to produce the bass that the smaller drivers are not capable of reproducing faithfully. While some media may not contain much low bass information, many types of rock, hip-hop, jazz, classical, or electronica rely heavily on low frequency content. In these cases, using a subwoofer will help fill out the sound and produce a more realistic experience. 

In home theater systems, there is a specific channel of sound specifically designed for the subwoofer, including most bass effects such as explosions, gunshots, and rumbles. Most home theater processors also contain settings to divert all low frequency content to the subwoofer, which frees the satellite speakers to play much louder and with less distortion. 

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How is a subwoofer amplifier's low pass active filter adjusted?

The lowpass filter on most subwoofer amplifiers can be adjusted between roughly 40 and 160 Hz. As an example of what it is doing, if we set the filter to 80 Hz, it will produce everything lower than 80 Hz. It is called a 'lowpass' crossover because it allows all frequencies lower than the crossover point to pass. Most home stereo speakers can work at their best down to 60-100 Hz, so we would like our subwoofer to begin making sound right about where the main speakers stop.

To find this setting, get the system up and playing music that has a good bass component. Adjust the subwoofer's volume so you can hear its output clearly. Adjust the crossover knob back and forth through its full range. As you increase the cutoff frequency to the point where it begins to overlap the main speakers, you'll hear the system begin to 'boom'. (If you have trouble hearing this change while standing very close to the subwoofer, go to the area where you would normally listen and have someone else adjust the knob for you.) Turn the knob back until the boom just falls away. Leave the knob set there. Optimize the volume of the subwoofer so it matches the main speakers, and you're done.

Once optimally set, your active subwoofer will require no further adjustment if used exclusively for either music or home theater. You may find that different settings work better for each situation, so take note of these. Because of this, often a remote controlled plate amplifier is used, or the enthusiast will have a separate system for music and home theater.

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What is the difference between an active and a passive subwoofer?

A passive subwoofer contains only a woofer in an enclosure with no amplification. An active subwoofer contains an on-board amplifier that will accept a low-level input and usually contains electronic crossovers. 

A passive subwoofer must be powered by an external amplifier and connected via speaker-level connection. Many times this passive subwoofer contains a built-in passive crossover that sends the bass to the subwoofer driver and passes the higher frequencies to the satellite speakers. This methodology is inherently difficult to implement and will usually result in very poor integration between the woofer and the satellites.

Using an active subwoofer system will almost always provide superior results due to the greater control in matching output levels and matching the crossover point between the subwoofer and satellites.

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Why is adjusting the frequency that comes out of the subwoofer so important?

We want the subwoofer to be a natural extension of our left, right, or center speakers in both volume and frequency. For example, let's say the subwoofer plays from 150 Hz and down and the main speakers in the system work from 40 Hz and up. Between 40 Hz and 150 Hz, both the main speaker and the active subwoofer are reproducing sound. This will cause these frequencies to stand out as a 'peak' in the response of the system. These overlapping frequencies will create 'boom' in this region that will detract from the performance of the entire system. Likewise, if the main speakers play from 150 Hz on up and the subwoofer plays only below 50 Hz, there will be a large 'hole' in the response that will reduce the impact and accuracy of the system.

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How do I match a speaker replacement to my current system?

The following link provides simple and BASIC information for those who need to replace drivers in their speaker systems and have little or no experience in loudspeaker design and selection. As there are volumes of text on the subject, this single page will not cover all bases needed for a FULL, in-depth understanding of all of the required background information in electronics, acoustics and other sciences involved. Any correspondance regarding the following content can be e-mailed to tech@Parts-Express.com

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Do you recone speakers?

Proper fit of the new surround is paramount in choosing a surround repair kit. The most critical area for a proper fit is where the inside flat of the surround overlaps the outer edge of the speaker's cone. If the new surround is very much too large or too small, you won't be able to glue them together. The surrounds must not be stretched, and can rarely be trimmed to make a proper fit.
 
The catalog page for the surround kits will show a suitable range of cone diameter for each kit. When measuring the cone, be sure not to include any of the old surround material in the measurement. For example, a 12' speaker will often have a cone diameter of about 9-1/4' to 9-1/2'. The kit will provide a proper fit if the cone's diameter is within this range. The outside diameter of the 12' kit's surround will be about 11-3/4'. This flat area is usually much wider than the inside edge and much less critical in fit.
 
The standard surround kits match dimensions commonly found on standard stamped-steel frame speakers. Cast-framed speakers or other proprietary-designed units can be difficult to impossible to re-foam without surrounds specifically intended for them.  

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How do I select the right speaker surround repair kit for my speaker?

A speaker that is called a 12' usually has an overall outside diameter of about 12'. So the same would also be true for 10', 8', and other standard size speakers. Common, stamped steel frame speakers will usually be within 1/4' of this diameter.
 
Cast aluminum-frame speakers will often have a larger diameter frame due to their construction. So what would otherwise be a 12' speaker based upon its physical and acoustic parameters, may have an over diameter of more than 13'.
 
Such dimensions aside, what is often more important to consider is the size of the cutout in the cabinet where a new speaker is to be mounted. Many speakers are listed here with dimensions 'A', 'B', and 'C'. The A dimension is the overall diameter. If there is a rabbet cut around the cutout, it must be large enough in diameter for a replacment speaker to sit into (flush mount), or completely overlap. The cutout size is B, which corresponds to the diameter of the hole into the inside of the speaker cabinet. The C dimension is the front to back depth of the speaker, and is rarely an issue outside of car audio application.   

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How do I measure my speaker?

Check out our Tech Talk forum, where hundreds of technicians, engineers, and hobbyists nationwide read and discuss electronics related questions each week. Feel free to read or participate yourself. 

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What is speaker phase? Is maintaining speaker polarity important?

Phase, with speakers, is the direction in which a speaker moves with relation to the AC input audio signal. When this AC signal is positive going, a speaker wired with correct polarity (+ to + and - to -) will move outward. A speaker wired with reverse polarity (+ to - and - to +) will move inwards.

Stereo speakers, generally speaking, will not have issue (technically) if they are both wired out of phase. This is due to the pressurization of air at the same rate as in the input, which amounts to the same frequency. When two similar speakers are wired out of phase with each other (one + to + and - to -, the other + to - and - to +) they will try to cancel each other's output. This usually is heard as suckout, lack of stereo imaging and a reduction of bass output.

Most speaker terminals are marked for correct polarity. They will either be stamped with a + or - mark, have on terminal larger (for the +) than the other (for the -) or are painted (red for +). However, this isn't always the case.

If a speaker is not marked for polarity, a simple method for determining polarity (on a midrange, woofer or subwoofer) is to use a AA battery and some spare speaker wire. Hold a wire in place on the positive terminal of the battery and connect it to what you believe is the positive terminal on the speaker, do the same with the negative terminal of the battery and the other terminal of the speaker. If wired in correct polarity, the speaker will pop and move outwards. Reverse polarity is indicated by the speaker moving inwards.

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Home Audio/Video

Can I use my home stereo or home theater receiver for whole-house audio?

Can I listen to different sources of audio in different rooms?

Do I need two powered subwoofers for my home theater?

When I hooked up the RCA cable to my receiver from my subamp, it began to make an audible hum. Is it defective?

What if I hear a buzzing noise in my speakers?

What is a subwoofer plate amplifier and why would I use it?

What is the best way to get the audio signal to the subwoofer amplifier?

I don't have a subwoofer out jack. What other connection can I use?

Can I connect another subwoofer amp to the low level output?

How are the high level inputs used?

Can I connect speakers to the high level output, but use the low level input?

Can I use one or more of the plate amps with my DJ rig?

What if the subwoofer hums when it is not plugged into anything but the wall outlet?

How do I stop my subwoofer from humming?

What if I hear a radio station thru my speakers?

Why should I add a subwoofer to my home theater system?

Do you have information to help me build my own home theater subwoofer?

What is the red and black wire on the back of the subwoofer plate amplifier used for?

How much power is needed for average home stereo or home theater?

What’s the difference between a receiver and an integrated amplifier?

What’s the difference between a pro sound amp and a home stereo unit?

If I have 250W speakers, should I purchase a 250W amplifier?

How do I connect my PC to my stereo or amplifier?

What are the parts of an IR repeating system?

Why doesn't my IR repeating system work?

Can I use my home stereo or home theater receiver for whole-house audio?

It is best that you don’t. Most impedance-matching volume controls and selector boxes use transformer-based protection circuitry. Home audio receivers do not have a power amplifier that is robust enough so as not to be negatively affected by what is referred to as a highly “reactive” load. Even when properly installed and adjusted, many receivers will run very warm, and may even go into protection mode as a nuisance. Some receivers may even be damaged, depending upon what protection circuits were built into them.

A common scheme is to use the home receiver as the source of audio, and use its line level outputs (tape line out or auxiliary line out) as the audio source for a two-channel power amplifier that was intended for use in sound reinforcement systems. Such amplifiers are commonly available at a lower price point than many home receivers, and can handle up to 16 of the impedance matching volume controls.

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Can I listen to different sources of audio in different rooms?

This is not an uncommon feature, but does require a much more sophisticated audio system. For a set of speakers in one zone to play a variety of input sources, it must have its own dedicated amplifier. These systems are set up in two common configurations.

The first is a unit containing 4, 6, or even 8 or more stereo amplifiers. In-wall zone controls are usually connected back to the main unit via a CAT-5 data cable, which allows the user to change the source of audio, and also control the volume of the speakers. Many will also allow the use of an IR remote control through the system to control connected components such as CD players, AM/FM receivers, etc. Other systems may even be controlled through a PC or laptop computer.

The second common type is called 'A-Bus', in which the wall plate controller actually contains the audio amplifier for the room or zone. Also connected back to a main unit via CAT-5 data cable, these systems often have inputs on the wall plate control for iPod, mp3, or other portable audio player for that and sometimes other zones. Features and price point vary greatly on these systems, and some will require the services of an authorized installer.

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Do I need two powered subwoofers for my home theater?

Unless the listening room is exceptionally large, you should not. The average listening room is about 1500 cubic feet. That is a room roughly 14' by 14' with an 8' ceiling. A good quality 10' or 12' subwoofer will generally produce sufficient levels in this size room for most listeners. However, if more extreme output levels are desired, or if the room is very large, multiple woofers can be used to achieve the desired output. Also, often a single subwoofer will sound good in some locations within the room, but lacking in other locations. Using two subwoofers may help even out the bass response throughout the room.

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Can I shield my powered sub so it does not affect my TV set?

Shielding the very large and powerful voice coil in a powered subwoofer is very difficult and often impossible. If the driver itself is not fully shielded, it is very difficult to shield the subwoofer as a whole. Most newer LCD and plasma TVs, if not all of them, are not susceptible to the stray magnetic fields created by speaker magnets.

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When I hooked up the RCA cable to my receiver from my subamp, it began to make an audible hum. Is it defective?

Likely it is NOT defective. What you are hearing is called a 'ground loop' and is caused by uneven ground potentials at various locations in your audio system. These potentials cause small levels of electricity to flow through the ground paths, which will often be amplified as a 60 Hz hum.

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What if I hear a buzzing noise in my speakers?

This is usually from external sources such a fluorescent lights and light dimmers. Fluorescent lights radiate electro-magnetic interference (EMI) that can get into a bad or cheap RCA patch cable. Low voltage light dimmers often put noise directly onto the house electrical wiring. Test by turning these types of lighting off, making sure that the dimmer has a complete 'off' position. Many of the 'slider' or 'rotary' dimmers do not have a completely off position even when at their lowest setting. If this is determined to be the source of the problem, try changing the circuit into which the subwoofer is plugged. As a last resort a line level ground loop isolator or isolation transformer has been seen to improve this problem on occasion.

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What is a subwoofer plate amplifier and why would I use it?

A subwoofer plate amplifier is a type of amplifier that is usually used in making active powered subwoofers. They are an aluminum plate with inputs, controls, and heat sinks on one side and the amplifier section and other electronics on the other. They're intended to be mounted into a cabinet with the subwoofer driver, and have features to optimize them for subwoofer duty. By using a plate amplifier in the subwoofer cabinet, the need for an extra external amplifier can be eliminated, which is very useful in home theater situations. Other benefits of using a plate amplifier are the ability to have independent volume control from the other speakers, a built in low-pass crossover, and the ability to adjust the phase of the subwoofer.

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What is the best way to get the audio signal to the subwoofer amplifier?

If your system is a relatively new multi-channel home theater receiver, it will have an 'LFE' (low frequency effect) or subwoofer output. This is a single or dual-mono RCA jack output and is the best way to get the signal from the processor to the subwoofer.

The output level of this jack will change in unison with the main volume control of the receiver, meaning that once you set the relative level of the subwoofer it should always match the main speakers. This jack also usually has an adjustable output level that can provide more or less signal to the subwoofer, useful in 'fine tuning' the bass levels. Usually the default setting of 0 dB will work well with most subwoofers, but in some cases raising or lowering this may be necessary. Generally we want the subwoofer's volume control to be set near 50%.

In instances where there is not an LFE output on a receiver, the Tape Monitor output may be used.

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I don't have a subwoofer out jack. What other connection can I use?

 The next best connection possibility is using the speaker, or high-level, connections. This input on the plate amplifier receives the signal that is normally sent to speakers and converts it internally into a smaller signal that it can use. This can be implemented either as a loop-through or as a straight feed. When used with small main speakers, it may be beneficial to route the speaker signal through the high-level inputs, and then connect the high-level outputs to the satellites. This provides a 6 dB/octave highpass crossover to the main speakers which will help protect them from receiving too much bass information.

The other possibility is to 'parallel' the speaker input connection with the feed going to your main speakers. Because the input impedance is very high on the high-level inputs, this method usually will not strain the main amplifier. This connection method can be used with main speakers that are relatively robust on their own, and if they have a steep low-frequency rolloff, decent integration between the subwoofer and the mains is possible. Many people try to use a 'Tape Monitor' loop to feed the subwoofer amplifier, which will work, but the level will not adjust as the main level is adjusted. Since you have to re-set the relative subwoofer level every time you use your speakers, it becomes a very annoying prospect.

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Can I connect another subwoofer amp to the low level output?

No you can't. There is an active highpass filter in the sub amp that rolls off everything below 150 Hz from the signal output here. With this high-pass output, a second sub amp will produce very little if any bass from this connection. This low level output is designed to be connected to another amplifier or receiver with full-range speakers. If you need to connect a second subwoofer amplifier, simply use a 'y adapter' before the inputs to provide multiple low-level signals. 

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How are the high level inputs used?

The high level inputs are generally used in stereo systems having small speakers that product little or inadequate bass. The speaker wire from the receiver connects to the input binding posts, left and right channels. The subamp takes its signal through a 1K ohm resistor on each channel and sums the two. The high level output is then connected to the full-range speakers and has a shallow highpass crossover at roughly 150 Hz. The lowpass active filter on the subamp will generally need to be set relatively high, though this will vary depending on the main speakers.

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Can I connect speakers to the high level output, but use the low level input?

No. If you don't use the high level input, there is no high level output. Similarly, if there is no low level input, there is no low level output.

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Can I use one or more of the plate amps with my DJ rig?

The plate amplifiers are generally intended for home stereo or home theater use, and are not ideally suited for the rigors of continuous DJ duties. However, if used responsibly with easy loads and not driven to their maximum levels for long periods of time, they will perform acceptably in a DJ setup. The main problem is overheating due to the prolonged high levels of output. There are many inexpensive pro-sound amps on the market that are designed for this use and will generally produce more reliable results.

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What if the subwoofer hums when it is not plugged into anything but the wall outlet?

If there are mechanical hums or consistent loud hums coming from the speaker when nothing is connected, then it is likely defective. Contact tech@parts-exspress.com for assistance.

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How do I stop my subwoofer from humming?

One of the first things to try is changing the outlet into which the subwoofer power is plugged. Since often a subwoofer is located away from the rest of the equipment, many times the outlet will be on a different circuit or have a different grounding point. Try connecting the subwoofer to the same outlet as the rest of your equipment via an extension cord or power strip. The next thing to check is the cable TV feed going into your system.

While this at first seems like a silly idea, if you consider the web of connections in your A/V system, it begins to make sense. Temporarily unhook the main cable connection and see if the hum stops or is reduced. If it does, the easiest solution is to purchase a coax isolation transformer such as our #180-075.

If this does not completely solve the problem, try unhooking the connections of different components in the system and see if the problem stops. If it does, consider using a line-level ground loop isolator in that location. Our works well. If nothing seems to quite eliminate all hum, the Ground Loop Isolator can be used directly on the subwoofer line-level feed and generally will solve most problems.

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What if I hear a radio station thru my speakers?

This is almost always a bad patch cable with leaks in the shield. Replace with a new or known good cable.

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Why should I add a subwoofer to my home theater system?

Sub-bass frequencies can be considered to be the foundation upon which to build an accurate and realistic home audio system. Subwoofers reproduce the lower frequencies that other speakers cannot reach, and they can do it with clarity, punch, and depth. As time passes, music and entertainment styles change and evolve. Today's music and cinema sound reproduction systems have to deliver performance that will satisfy the audience's elevated expectations. It is obvious that the quality of the midrange and high frequency components must be optimized because so much critical information is found in those ranges. The use of a subwoofer is of equal importance, however, because a sub will help to fill out the lowest musical octaves of sound and provide a more realistic listening experience. It should be mentioned that bass does not need to be overbearing or exaggerated, but rather, it can be a subtle yet important enhancement to almost any style of music or program.

Home theater systems bring the excitement and realism of a traditional big-screen movie into a viewer's living room. The same multi channel sound track techniques that are used for full sized movie theaters are also part of the home movie experience. Surround sound, center channel speakers, and dedicated subwoofer channels are all elements that work together to create a three dimensional soundstage. The subwoofer does its part by supporting the musical program, and also by providing the acoustical 'muscle' that will move the air required to shake, rattle, and roll the viewer with specific low frequency accents. The reproduction of these effects in the form of a physical sensation places the user in the middle of the action, and increases drama and impact. We believe that a true theater experience cannot be attained without the use of a subwoofer.

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Do you have information to help me build my own home theater subwoofer?

There are quite a few really good subwoofer systems on the market today that give excellent performance. for a price. We have seen home subwoofer systems at high end hi-fi shops sell for as much as $5000. While $5000 will certainly get you one heck of a home theater experience, most of these subs will contain less than $1000 in materials. Likewise, many $1000 subs have less than $250 in materials. With a few common tools, a weekend or two of your time, and some elbow grease, Parts Express can show you how to build a sub that will perform like the commercially available ones and save you money.

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What is the red and black wire on the back of the subwoofer plate amplifier used for?

Availability or non-availability of schematics for the electronic products we offer is the decision of the manufacturer. Most consumer electronics do not come with schematics, and most companies regard it as being proprietary information which they will not share with us, or provide to end users. We display all information supplied to us within a product's web page.   In the unlikely event you need information not displayed, please email tech@parts-express.com to research an answer for you.  

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How much power is needed for average home stereo or home theater?

Actually, not very much power at all. The average woofer found in a set of home stereo speakers will have an SPL number of 85 to 90 dB 1W/1m. SPL stands for sound pressure level. As an example, a running lawn mower will create an SPL of about 88 dB as measured from a meter’s distance. Therefore, a speaker with an SPL of 88 dB will be as loud as a running lawn mower while driven with 1 Watt of power, from the distance of a meter (1W/1m).

So, if you were sitting in front of your home stereo speakers and they were being driven with an average continuous power of 5 Watts, you would probably find them to be uncomfortably loud. As a practical thing, for home audio or home theater, the power capability of your system only needs to be great enough to reach the peaks in the audio program. So it makes little difference if your amplifier or speakers can deliver or handle 50W or 200W of continuous power, if they’re already too loud at 5W of continuous input power for average listening. 

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What’s the difference between a receiver and an integrated amplifier?

Both are home stereo units that contain a preamplifier, often tone and balances controls, and have multiple inputs for CD, audio cassette, DVD, etc. A receiver has the same features with the addition of an AM/FM tuner (receiver).

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What’s the difference between a pro sound amp and a home stereo unit?

The differences are many, and important. As with about anything, using a device for the application for which it was intended is always best. Pro sound amplifiers generally have a single set of input connectors that are different than home units employ, often have no controls other than a separate volume control for each channel, and do not contain a preamplifier. They are designed to be mounted into an equipment rack and often have cooling fans that run audibly, and sometimes continually. These amplifiers often have very high power and current capabilities, and are designed to withstand the rigors of set up, tear down, and transportation of the sound system of which they are part.  

Receivers and integrated amplifiers have multiple inputs, preamplifiers, tone and balance controls, and many other possible features which make them far more suitable for the home listening environment. A home audio receiver would make a poor amplifier for a sound reinforcement or PA system, just as a PA amp would be a poor choice for home audio.

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If I have 250W speakers, should I purchase a 250W amplifier?

Not necessarily, but it definitely depends upon the application. For a PA or sound reinforcement application, if you need to wring every last bit of sound pressure that a 250W speaker can provide (not recommended), you would go with a 500W amplifier. The thinking here is that a 500W amplifier could reach 250W without distorting or “clipping” the output signal. Such a distorted signal can quickly damage a speaker’s voice coil.

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How do I connect my PC to my stereo or amplifier?

Most modern PCs and laptops have multiple 3.5 mm jacks for both audio inputs and outputs. Typically these 3.5 mm jacks follow the color coding listed below:

Lime Green is for analog stereo line-level output for front speakers and headphones.

Pink is for analog non-powered microphone input (stereo or mono).

Light Blue is for analog stereo line-level input (such as from a stereo or mixer).

Light Purple is for analog rear/surround line-level output.

Orange is for analog center channel/subwoofer (left + right summed mono) line-level output

Black is for digital audio output (for connection to a surround receivers coaxial digital)

For the analog audio inputs and outputs, only a standard stereo 3.5 mm plug to dual RCA audio jack adapter is needed. Connect a standard RCA patch cable from the adapter to your stereo or amplifier. Most Windows PCs have two independent software based mixers. If you have a problem with sound make sure you check the sound settings in the Control Panel, then the software mixer installed with your soundcard/motherboard drivers.

For connecting the digital audio output of your PC to your stereo, use a standard 3.5 mm mono to RCA adapter. Connect a digital coaxial cable from this adapter to your stereo. If you have difficulty with sound output, check your sound settings through Control Panel (in Windows) for a digital audio output setting to be ticked. Also check to see if there is an additional software based mixer that installed with your soundcard/motherboard drivers. There may be an option to select digital audio output there as well.

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What are the parts of an IR repeating system?

For the purpose of this FAQ, only wire based IR repeating system is covered. Typically IR repeating systems consist of three basic parts: targets (also known as receivers), emitters, and hubs.

Targets are mounted at the location from which you want to control remote located audio/video gear (or anything else the uses an infrared remote control). Targets are three-wire devices, one wire for +9 to +12 VDC power, one wire for ground, and one for signal. Infrared signal is captured by the target and converted to a DC pulse which is sent to the hub. Targets come in various forms such as tubes (used for mounting to a panel or cabinet), set-top boxes, small low-profile targets that attach to TVs, and Decora-style target plates. Category cable (known as Cat 5) is often used for extended cable runs from the target to the hub. The four pair category cable is often wired with each pair being combined for a single target wire. It is recommended to connect the spare pair of wires to ground.

Infrared hubs provide a central connection point for the IR repeating system. Typically a +9 to +12 VDC power supply is connected to the hub for system power. Targets connect to the hub via set screws, with optional multiple targets connected in parallel. Emitters are connected to the hub via 3.5 jacks. Most hubs have a provision for a test LED that flashes when a DC pulse is sensed. This can aid in system troubleshooting.

Emitters take the DC voltage sent from the targets, through the hub, and convert the voltage back to an IR signal. Most emitters have a double-sided adhesive that enables them to be affixed to the IR window of the components to be controlled by the IR repeating system.

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Why doesn't my IR repeating system work?

The first step in troubleshooting an IR system is double checking the wiring. Often signal, power, or ground have been swapped at either the target or the hub.

The second step in troubleshooting is to consider lighting local to the target. Lighting sources can emit interference that inhibit a target's ability to receive IR signal. CFL (compact fluorescent light), flourescent tube lighting, as well as light emitting from plasma and LCD TVs are known to interfere with some systems. Powering off these light sources should restore operation if they are the culprits.

For extended runs over 100 feet or more, you make need to take a third step and try a power supply with a higher current output rating.

Lastly, some manufacturers are starting to use IR systems that are above the usable frequency range of the target. Many components operate in the 38 kHz band, but newer components are moving towards the 56 kHz band and higher. If the above three steps do not solve your problem, and you are getting an LED indication of operation at the hub, you may want to try a wide bandwidth target with response up to 100 kHz.

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Car Audio

Why do I need a stiffening capacitor?

What is a stiffening capacitor?

How does a stiffening capacitor work?

Where should the stiffening capacitor be mounted?

What size stiffening capacitor do I need?

What voltage capacitor do I need?

Do stiffening capacitors require special handling

How do I install acoustic damping sheets?

Do you carry aftermarket installation kits?

Do you sell aftermarket harnesses?

Do you sell aftermarket dash kits?

Do you have wiring diagrams?

Why do I need a stiffening capacitor?

Stiffening capacitors can help your automotive amplifier deliver more output on peak bass transients.  Low frequency causes the most power draw in an amplifier, so automotive subwoofer amplifiers are the main application for stiffening capacitors. 

Like any other electrical power supply system, automotive charging systems have a finite capability in the amount of power they can supply both continuously and at peak.  Adding a stiffening capacitor to your system can improve transient response in an audio system while run at high output levels, and can reduce flickering dash lights, to a point.  It should stand to reason that an amplifier cannot draw power from the charging system beyond what the charging system is designed to produce.

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What is a stiffening capacitor?

A stiffening capacitor is an extremely large value electrolytic capacitor.  Capacitors have the ability (capacity) to store a charge on their 'plates'. The larger the capacitance, measured in units of Farad, the greater the charge a capacitor can store for a given voltage.  Most automotive capacitors can store a charge at 16 to 20 volts, and are rated from about .5 Farad up to 2 Farad or even more.  Capacitors have an extremely low internal resistance to current flow, much lower than that of a battery. Capacitors can therefore charge and discharge power much faster than a battery can.

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How does a stiffening capacitor work?

All capacitors consist of two 'plates', separated by an insulator called the 'dielectric'.  Each plate has an external connector.  Connected to a source of voltage, electrons are forced onto one plate, and off of the other plate.  When the capacitor is fully charged, no more electrons will flow in or out.  Disconnected from the source of voltage, the charge will remain between the plates, and the voltage can be measured between the capacitor's terminals with a volt meter.  A capacitor can store a charge for a very long time.  . 

The capacitor is connected to the positive power line to the amplifier, and then grounded to the vehicle chassis.  When initially connected, the capacitor will very quickly charge up to the voltage of the vehicle's battery, usually a little over 12V.  So quickly, in fact, that a large spark will occur unless a small resistance is used to slow the rate of charge.  

Low frequency causes the output transistors in any audio amplifier to remain on and flowing current to the speakers for a longer period than midrange or high frequencies. Low frequency therefore creates the greatest current draw in any audio system.  As the source of low frequency in music is usually a drum or bass guitar, the low frequency is mostly in short bursts, or 'transients.'  So subwoofer amplifiers generally draw the most power from an automotive charging system. 

When a motor vehicle is running, the power for the electrical system comes from the alternator.  Some very high power subwoofer amplifiers are capable of drawing more power from a vehicle's charging system than the alternator can produce.  At very high output levels, this can cause the bass 'hits' to begin to lose volume, punch, and overall clarity, and can cause lights to dim or flicker.  When the amplifier tries to draw more power than the alternator can produce, the voltage in the power line to the amplifier (and everywhere else in the electrical system for that matter) begins to drop. 

As the voltage in the capacitor is still at 12V, the drop in voltage in the line will cause the capacitor to push charge onto the power line.  This bolsters or 'stiffens' the voltage in the electrical system until the transient bass 'hit' passes.  At that time the demand by the amplifier drops, the alternator brings the voltage back up, and the capacitor recovers its charge.  It is then ready for the next bass transient. 

This power 'reservoir' in the capacitor only works to a point. If the power draw from the amplifier or multiple amplifiers demands so much power that the alternator can't bring the charging system and capacitor back up between bass transients, then reduced bass response and flickering lights will again occur.  Adding more capacitance may help, but an alternator with a higher current rating would be a better solution.

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Where should the stiffening capacitor be mounted?

Power cable does display resistance to current, and dissipates a bit of power itself.  The stiffening capacitor should be connected into the circuit as close as possible to the amplifier for the greatest benefit to the sound system, and usually is easiest mounted in the trunk area of a vehicle.

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What size stiffening capacitor do I need?

As a general rule, 100,000 Microfarad (.1 Farad) per 100 watts of amplifier power is recommended. So a 1 Farad capacitor should work up to about 1000 watts.  Remember that the subwoofer amplifier is not the only drain upon the charging system, just the one that causes its limitations to show up first.

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What voltage capacitor do I need?

Automotive battery charging systems typically vary from as low as 12VDC up to about 14.5VDC, with the average alternator output at 13.8VDC.  Most stiffening capacitors are rated at 16V/20 surge, or 20V/24 surge.  Do not use capacitors rated below 16VDC, though a greater voltage rating is fine.  Over-voltage can quickly destroy a capacitor, and must be avoided.  Over-voltage transients can occur in the charging system, which is why a 20V or greater stiffening capacitor is generally recommended.

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Do stiffening capacitors require special handling

Handle stiffening capacitors with the same care as you would a car battery.  Also of concern is the initial charging of the capacitor, or if you want to discharge the capacitor for storage.  Having an extremely low internal resistance and great capacity for holding charge, they can create arcing and sparks during charge and discharge. As a result, you should not connect 12 VDC directly to the terminals of an uncharged capacitor.  At best, the arcing will deface the connectors. Most capacitors are supplied with a charge/discharge resistor, through which the capacitor is to be charged or discharged.  It can take up to about a minute for the cap to reach full charge or complete discharge when using the resistor.  Be aware the resistor may become hot during the process.  
 
In order to determine that the stiffening capacitor is completely charged, connect a multimeter in parallel with the capacitor terminals ( + to +, - to -). Once the DC voltage stabilizes to the capacitors rating (12-20 VDC) the capacitor is completely charged.
 
 

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How do I install acoustic damping sheets?

This inexpensive, multi purpose noise reduction material damps and absorbs vibration from virtually any solid to which it is securely attached. Read our step by step guide.

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Do you carry aftermarket installation kits?

Yes!  Metra mobile sound installation kits provide a quick and simple way to install aftermarket audio equipment in the your vehicle.

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Do you sell aftermarket harnesses?

Yes. Purchased based upon the make and model year of the vehicle, they are available in three types:

The most commonly needed is called an 'into-car' harness. This allows you to install an aftermarket head unit (in-dash radio/player)  into a vehicle without having to cut off the factory plug which was designed to fit the original OEM unit. Into-car harnesses plug into the vehicle's harness, and provides labeled wire leads which are then connected to the wire leads of the aftermarket head unit's harness. This negates having to find a wiring guide for the vehicle's audio harness, and the OEM radio can be easily reinstalled if desired. 
 
The second type harness is an 'OEM harness', which plugs into an OEM head unit (from another vehicle). It provides the needed labeled wire leads. An into car harness is then connected to the OEM harness, and plugged into the vehicle into which it is being installed.
 
The last type is an amplifier bypass harness which allows an aftermarket head unit to be installed into a vehicle that came with an 'outboard' audio power amplifier. These are often referred to as 'premium' sound systems. These harnesses can also allow door chimes and other audible warnings, GPS and satellite-based services to continue to work through the vehicle's speakers.

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Do you sell aftermarket dash kits?

Yes. They are available for most domestic, and many import vehicles. They are purchased based upon make and model year, and often can accommodate other devices and controls that are part of the dash near the head unit.

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Do you have wiring diagrams?

Yes. Referred to as 'The Disc' by Omega, the company who provides the product, it is a CD-ROM that covers literally thousands of vehicles. It provides wiring diagrams to aid in installing audio systems, alarm systems, remote start, power door locks, and more. Bear in mind that it can take two or more years for information to be compiled on a new or redesigned vehicle.

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Do you sell aftermarket housings?

We do sell an aftermarket housing to allow mounting a standard DIN-size (7' x 2') in-dash unit either under-dash or overhead. It is Metra's Universal Radio Housing, 99-9000.

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Commercial Sound

What kind of a speaker system is used for announcements, paging, and background music?

Should a commercial sound system be run in stereo?

What is a 70V speaker system, and how does it work?

Why would a 70V speaker system be better for my business than another type?

How many speakers can I connect to a 70V system?

How is a 70V system set up and adjusted?

Can I control the volume by any other means than at the amplifier?

Is a speaker for a 70V system different than “regular” speakers?

What kind of wire do I need for a 70V system?

How do I determine how many speakers I need for a given area?

Can you explain the basics of 70-volt Audio Systems?

What kind of a speaker system is used for announcements, paging, and background music?

Such sound systems are rarely run in stereo, or as a two channel system. Any benefit from stereo sound only comes from the listener’s seating position as related to two stereo speakers. Commercial systems are intended for paging, announcing, and background music. So long as such a system has reasonable frequency response so that music sounds “full range” with lows and highs, voice intelligibility, a reasonable volume level is about the only other requirement. The volume level required is often a function of ambient noise such as a large crowd, engine noise, operating machinery, etc.

 

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Should a commercial sound system be run in stereo?

A 70V speaker system is the most common type of commercial sound system, with 25V and 100V also available. The amplifiers and speakers are designed specifically for the application as they transfer power to the speakers mostly as voltage, rather than mostly as current flow in a more standard amplifier/speaker system. A 25V system may be used in a small doctor’s office or restaurant, while a 100V system might be used to put a sound system throughout a golf course. 

 

The main difference between a standard audio system and a 70V system is how power is transferred to the speakers. Rather than the output of the amplifier driving the speakers directly through the speaker wire, the amplifier drives the input side of a voltage step-up transformer. This transformer is internal, and is the main difference between these and standard power transformers. The output side of the transformer produces the audio signal with the voltage greatly increased (the current is decreased by the same ratio), usually up to 70V at max. This voltage is used to overcome the comparatively high impedance and resulting signal loss from long runs of speaker wire. At each speaker in the system, there is a small transformer that steps the voltage back down to a useable level for the speaker.

 

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What is a 70V speaker system, and how does it work?

The benefits of such systems are several, and significant! A major advantage of a 70V system is the ease of wiring the system. All speakers are wired to the amplifier in parallel. You can therefore run the wire from speaker to speaker, and also “tap in” to a run of speaker wire at any point to go off to more speakers in another area. Such a system could be implemented using series/parallel combination wiring schemes to maintain a reasonable load on the amplifier. But such a set up can be inflexible if added speakers are needed, and difficult to troubleshoot if problems arise. 

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Why would a 70V speaker system be better for my business than another type?

This depends mostly upon how loud each speaker needs to be. But more specifically, it is how much power will be drawn by each speaker to reach that volume level, and the power capability of the amplifier. The simple answer is to start with 80% of the total amplifier rated power output, ie. an amplifier rated at 100 watts RMS would give you 80 watts of reliable usable power. Divide this number by the total amount of speakers you would like to use, and this would be the maximum tap setting for each speaker. If you start with 80 watts and 40 speakers, you wouldn't want to exceed 2 watts per speaker. You are able to increase power to each speaker if you reduce the total amount of speakers, and vice versa.

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How many speakers can I connect to a 70V system?

The transformer located on each 70V speaker provides four input “taps”, each having a different input wattage rating. Commonly, these are .5W, 1W, 5W, and 10W. For a given setting of the amplifier’s volume control, the higher the wattage tap used on a speaker, the more loudly it will play. This makes adjusting the system much easier and efficient as it is common for some speakers to always play louder than others based upon where they are.

For example, one system may need to operate speakers in both an office area and a warehouse area. With a low level of ambient noise in an office, the speakers will not need to play loudly to be easily heard. But in a warehouse area, the ambient noise can be significant, and the speaker will need to play more loudly. One speaker may also need to cover a larger area than another as well. So the office speakers might be tapped at .5W, while the warehouse speakers may be tapped at 5 or 10W.

The rule of thumb for setting up a 70V speaker system is that the sum of the speaker wattage taps used should not exceed 80% of the amplifier’s maximum power output. So a 100W amplifier could easily drive 80 speakers, all tapped at 1W. Or, 16 speakers all tapped at 15W. So long as all of the taps do not add to more than 80% of the amplifier’s power capability, the system will remain stable and should provide a long service life.

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How is a 70V system set up and adjusted?

70V volume controls are also commonly used in areas where it may be necessary to turn the speaker down or off. These mount into a standard junction box, the speaker wire goes to the volume control first, then on to the speaker or speakers. 

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Can I control the volume by any other means than at the amplifier?

Most 70V speakers are otherwise standard in their construction and are usually 8-ohms impedance, whether a ceiling-mount, weather-proof cabinet, or horn type design, and are adapted for 70V systems by use of a transformer. The transformers can be purchased separately, so virtually any 4 or 8-ohm speaker can be converted for use with a 70V system.  

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Is a speaker for a 70V system different than “regular” speakers?

As 70V systems transfer power with low current, an 18 or 16 gauge speaker wire is most commonly used. Installation or “architectural” speaker wire is used almost exclusively for these systems, and especially when the wire must be pulled through walls, around beams and supports. This type wire has a slick outer jacket made of PVC. This eases pulling the wire, and lessens the chance that the wire would be stretched or broken during pulling.

The great majority of such wire products are Class 3 rated and UL approved. This means that they will pass an electrical code inspection. For outdoor applications, a direct burial type wire should be used whether the wire is to be buried in the ground or not. Unaffected by heat, sun, and moisture, such speaker wire will provide a much longer service life when used outdoors.

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What kind of wire do I need for a 70V system?

This is where professional installers earn their keep! For an office area with an 8’ ceiling, one ceiling speaker can easily cover an area 20’ by 20’. A higher ceiling allows a single speaker to cover a larger area, but it must be set up to play a bit louder. A high ambient noise level is also a major consideration for machine shops, warehouses, etc. These areas usually don’t benefit from music, though paging is often needed and must be intelligible. Horn-type speakers are often used for these areas as they are more directional and can be installed to get the best coverage with the fewest number of speakers.

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How do I determine how many speakers I need for a given area?

The red and black wires exiting the back of the amplifier is the hook up wire to connect the subwoofer amplifier to the speaker.

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Can you explain the basics of 70-volt Audio Systems?

Audio distribution systems, especially those commonly used in department stores, warehouses, around race tracks, etc., require that many loudspeakers be driven from a single audio amplifier over long runs of speaker wire. It is certainly possible to connect 20 or 30 speakers in series/parallel combinations to achieve a reasonable impedance speaker load for the amplifier. But this type system can be difficult to install and troubleshoot, and can be unreliable and inflexible. We're here to help you learn more about these systems!

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Wire/Cable

What gauge cable do I need for my project?

What is the difference between wire and cable?

What is coaxial cable?

What is meant by 75-Ohm cable?

What does RG stand for, in terms of cable?

How far can you run a coaxial cable like RG-6?

What type connectors are used with coaxial cable?

What is the difference between crimp and compression connectors?

What is Quad-Shielded coaxial cable?

What is meant by Oxygen Free speaker wire?

Is heavy gauge speaker wire such as 10 or 12 gauge necessary?

What type connectors are used on speaker wire?

What is TRS?

What is plenum wire or cable?

What is direct burial cable?

Is speaker wire shielded?

What are Cat 5 and Cat 6 cables?

Can Cat 5 be used for audio applications?

What gauge cable do I need for my project?

Power Cable Calculator

Total System Amperage DrawUp To 4 ft.Up To 7 ft.Up To 10 ft.Up To 13 ft.Up To 16 ft.Up To 19 ft.Up To 22 ft.Up To 28 ft.
0-20A14 ga.12 ga.12 ga.10 ga.10 ga.8 ga.8 ga.8 ga.
20-35A12 ga.10 ga.8 ga.8 ga.6 ga.6 ga.6 ga.4 ga.
35-50A10 ga.8 ga.8 ga.6 ga.4 ga.4 ga.4 ga.4 ga.
50-65A8 ga.8 ga.6 ga.4 ga.4 ga.4 ga.4 ga.2 ga.
65-85A6 ga.6 ga.4 ga.4 ga.2 ga.2 ga.2 ga.0 ga.
85-105A6 ga.6 ga.4 ga.2 ga.2 ga.2 ga.2 ga.0 ga.
105-125A4 ga.4 ga.4 ga.2 ga.0 ga.0 ga.0 ga.0 ga.
125-150A2 ga.2 ga.2 ga.0 ga.0 ga.0 ga.0 ga.00 ga.

The above chart shows wire gauges to be used, if no less than .5 volt drop is accepted. If aluminum wire or tinned wire is used, the gauges should be of an even larger size to compensate. Cable gauge size calculation takes into account terminal resistance. Wire gauge recommendations based on IASCA guidlines

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What is the difference between wire and cable?

The two terms do have specific definitions, though are commonly used interchangeably, even by manufacturers of such products. By definition, a cable has a shield to help block electro-magnetic and radio-frequency interference (EMI and RFI), a wire does not. So “RG-6 coaxial cable”, and “12 gauge speaker wire” are correct.

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What is coaxial cable?

The term “coaxial” simply means “sharing a common axis”. Coaxial cable has a single center conductor (the axis), surrounded by a dielectric material, a braided wire shield, and an outer insulative jacket. It is specifically designed and intended for use as a transmission line to carry radio frequency signals. It is therefore commonly used for connecting commercial cable, broadband internet, and antennas to their transmitters and receivers.

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What is meant by 75-Ohm cable?

The term refers to the characteristic impedance of a radio frequency cable. It was learned through experimentation in the early 20th Century that this impedance offered the least signal loss of radio frequency line transmissions. Cables such as RG-6, RG-59, and RG-11 are all 75-Ohm type cable. 

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What does RG stand for, in terms of cable?

Radio Guide, which suggests that the cable is intended for radio frequency applications.

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How far can you run a coaxial cable like RG-6?

100 feet is generally considered to be about the limit that coaxial cable can be run before signal loss and degradation becomes an issue. Amplifiers are commonly used for extended runs of coaxial cable.

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What type connectors are used with coaxial cable?

The connectors most commonly used with coaxial cable are called “F” connectors. The male connector is installed on the cable, with input and output devices having female connectors. These are threaded connectors and are of two general types: crimp and compression. Such connectors are purchased based upon the size coaxial cable being used. An F connector for RG-6 will not properly fit RG-59.

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What is the difference between crimp and compression connectors?

Crimp-type F connectors are the most common, and require a “hex crimp” tool. These crimp tools are generally in the $20.00 price range, and must also have the correct size crimp for the connector being used. Some have die sets available for different types and sizes of connectors.

Compression connectors are generally intended for professional installations. They contain a ring of a tough plastic material that folds in on itself when the connector is compressed with the installation tool. The collapsed ring grips the outer insulation to make a secure and weather-proof seal between the cable and the connector. These connectors and installation tools can be much more expensive than the crimp type, and can take some practice before a good connection between the cable and connector is achieved every time. For most applications, the crimp type is more than sufficient.

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What is Quad-Shielded coaxial cable?

Usually available in RG-6, quad-shielded coaxial cable has additional shielding added for severe environments where radio frequency and electro-magnetic interference (RFI and EMI) can create “noise” issues with standard coaxial cabling.

Industrial and manufacturing facilities using welders, large electric motors, etc., may need the more heavily-shielded cable to block severe interference. For all residential and most other applications, the extra shielding is unnecessary. Quad cable does require a different F connector than standard RG-6. This connector also requires the proper hex crimp tool be used.

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What is meant by Oxygen Free speaker wire?

Copper will slowly corrode when in contact with the oxygen in the air. Oxygen free speaker wire is made by extruding the insulation onto the stranded copped wire in an oxygen-free environment. Sealed from the outside air inside the insulation, the copper is not as susceptable to corrosion and oxidation as standard speaker wire.

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Is heavy gauge speaker wire such as 10 or 12 gauge necessary?

It does depend somewhat upon your application, but for home audio, the answer is generally no. The runs of speaker wire in a home system are comparatively short, and the power levels are not high. 16 gauge speaker wire will perform indistinguishably from 12 or 10 gauge wire in most home audio applications where power levels are below 100 watts per channel.

High power pro sound systems such as in a concert venue benefit from larger gauge speaker wire as the runs of speaker wire are comparatively long, and the power delivered to the speakers much higher than in other audio systems. Too small a gauge of wire for the length run and current carried can cause the wire to warm, which will further drop power reaching the speakers.

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What type connectors are used on speaker wire?

The most common connectors used on speaker wire are ¼” phone plugs, banana plugs, and speaker pins.

The ¼” plug was originally designed in the early 20th Century for use in telephone switch boards. It is the only audio connector that is used both as a line or signal level interconnect (i.e. electric guitar cord), and for power connections between amplifier and speakers. The tip of the plug carries the audio signal, the “sleeve” is ground and is connected to the cable’s shield in line level applications.

Banana plugs have recently become popular in home audio, but have been used in pro sound systems for some time. They are designed to work with “binding post” type output connectors. The main benefit of a banana plug is that they are “stackable”. This means that two speaker wires with banana plugs can be plugged into the same binding post output of an amplifier. Though common in pro sound systems, this feature is rarely used in home audio.

Speaker pin connectors are also used, but are not as common as they once were. They are intended to be inserted into the hole in the shaft of a binding post, and secured in place with the nut. This is more convenient than inserting stripped speaker wire into the binding post, and is certainly preferred when hook up and disconnect is done often.  

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What is TRS?

The acronym TRS means “tip-ring-sleeve”, and refers to a ¼” phone plug that bears three connections rather than two. They are easily recognized as different from the standard ¼” phone by having two insulator rings on the plug instead of just one. Often referred to as a “stereo ¼” phone”, they are commonly found on stereo headphones and some “balanced” circuits in pro sound equipment.

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What is installation or architectural speaker wire?

This type of speaker wire is designed for applications where the wire is to be pulled or installed inside walls, above drop ceilings, and in crawl spaces and basements. The construction of installation speaker wire generally has the two or more conductors separately insulated, with each having a different color of insulation. They are then covered with an outer PVC jacket. The jacket not only helps protect the wire from stretch and abrasion while being “pulled”, it has a smooth finish so it will slide more easily around studs, joists, beams and the like. This jacket also can help protect the integrity of the wire if a staple gun is used to secure the wire to studs or joists.  

Architectural speaker wire will be UL approved, and have a CL2, CL3, CMR, or plenum rating for different installation applications and fire code requirements.

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What is plenum wire or cable?

Plenum-type cable or wire will not create noxious or poisonous gases or fumes if the insulation material becomes hot or burns. Running cable and wire through air ducts (plenum) can be convenient and time saving for the installer, especially going between floors of a building. But if such wire became hot and the insulation burned, toxic fumes could be sent throughout the building via the ventilation system. Therefore, many electrical codes require that cable being used as such must have a plenum rating.

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What is direct burial cable?

Direct burial cable and wire are intended for use outdoors for speakers and other low voltage applications. The outer insulation is made from polyethylene, rather than polyvinylchloride (PVC). It not only can be buried directly into the ground without the need for conduit to protect it from moisture, it will also resist damage from UV in sunlight, which degrades many such materials over time. It is commonly run overhead between power and light poles.

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Is speaker wire shielded?

Speaker wire with shielding does exist, but is not common. It is rare that noise being induced into speaker wire comes from any source other than house wiring or other conductor carrying 120VAC/60Hz power. Speakers themselves are far to inefficient to make an audible sound from radiated sources such as light dimmers or radio broadcast.

Most problems are due to speaker wire being run very close to house wiring, or any conductor carrying 120VAC/60 Hz. Problems can be avoided by keeping any parallel runs of house wiring and speaker wire to a minimum, and by keeping them separated by as much distance as possible. If hum problems are absolutely unavoidable due to the installation requirements, a metal conduit must be installed to separate the speaker wire from the house wiring. Speaker wire should never be coiled and stacked with power wire.   

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What are Cat 5 and Cat 6 cables?

Category 5 and 6 are referred to as “data cable”. By industry standard, they consist of four twisted pairs of wire, for a total of eight conductors, 24 gauge wire is most common conductor used. Twisting the conductors of each pair together provides a shielding effect, making the circuit resistant to interference. The insulation color code on each strand is also an industry standard. This facilitates proper installation as each separate conductor must be connected to a connection block or modular connector in a specified order. Though other uses certainly exist, this cable is mostly commonly used to transfer digital data.

The difference between Cat 5 and Cat 6 is the bandwidth of the data that they can transfer. For industrial applications, these data cables are available with a foil shielding to enhance the cable’s resistance to interference from severe levels of EMI and RFI.

The connector used on Cat 5 cable (Ethernet) is commonly referred to as a RJ-45, but is correctly called an 8P8C modular connector.

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Can Cat 5 be used for audio applications?

Cat 5 is certainly not the best choice for use as speaker wire. But it has become very popular in applications where it is desirable to send a low level (line or preamp level) audio or video signal over a long distance of cable.

Such an application requires the use of a device called a “balun”, which stands for balanced/unbalanced.  The balun is a passive, transformer-based device. It changes the unbalanced, high impedance signal coming in on a single conductor interconnect such as an RCA, to a very low impedance circuit being carried on two conductors (balanced). It’s possible for an audio balun to allow a line level signal to be transferred up to 2500 feet through Cat 5 cable. Another balun, identical to the first, is required at the receiving end to convert the signal back to unbalanced and high impedance.

Baluns are also available to transfer HD audio/video and VGA (computer video format), via Cat 6 cable, though distances for different formats does vary.   


 

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Pro Sound

How do I install acoustic foam?

Do you have information to help me build my own pro audio subwoofer?

How do I choose the correct microphone for my needs?

Do you have a wiring diagram for the XLR Connectors?

Where can I learn more about Pro Audio?

If I have 250W speakers, should I purchase a 250W amplifier?

What is meant by clipping?

Should a pro sound amp be operated with its controls set all the way up?

How do I install acoustic foam?

ACOUSTIC FOAM INSTALLATION GUIDE



1. Before starting, make sure you have a clean and convenient work area for applying adhesive to the back of your foam sections. Clean all surfaces to be treated with acoustic foam to ensure proper adhesion.


2. For best results, apply spray adhesive to both the foam backs and the surfaces to which you will be attaching the foam. Spray the adhesive approximately 10 inches from the surfaces and use a back and forth movement, creating a web-like pattern.

3. Once the entire area has been treated with adhesive, wait approximately one minute for the adhesive to become tacky before joining the foam to the other surface. This will ensure a very strong bond. For a more temporary bond, spray only the foam back and not the other surface.


Most polyurethane and polyester open cell foams can be installed this way. Be sure to use an adhesive that is safe and appropriate for the foam that you're using.

 Temporary Mounting

You may prefer to mount the foam less permanently, or in a fashion that will not damage the drywall if the panels need to be removed at some point. Using standard straight pins and a tack hammer, drive four or five straight pins into the drywall at a downward 45-degree angle. A quarter-inch into the drywall is sufficient depth for the pins to support the foam panel. With a pair of diagonal cutters, cut the heads off of the pins, and simply press the foam panels onto the pins. When removed, the pins holes can be pressed nearly closed and flat with your fingertip, and can be covered easily with latex wall paint if necessary. This method also works just as well on any type of wood paneling.

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Do you have information to help me build my own pro audio subwoofer?

There are quite a few really good subwoofer systems on the market today that give excellent performance… for a price. It is not uncommon to see pro sound subwoofer enclosures with selling prices of $3000 or more. Some of these boxes reflect the use of advanced technologies and materials, and complex associated processors, but there are also some tried and true designs available to the custom builder that can offer very effective performance. With a few common tools, a weekend or two of your time, and some elbow grease, Parts Express can show you how to build a sub that will perform like the commercially available ones and save you money.

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How do I choose the correct microphone for my needs?

Microphones represent the interface between the acoustical energy in the air that surrounds us to the audio systems that we use to amplify, record, or otherwise manipulate sound. There are many different types of microphones designed for many different applications, though they all do the same basic task of converting the energy in sound waves into an electrical representation of these patterns. Continue reading...

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Do you have a wiring diagram for the XLR Connectors?

XLR Connector Wiring Diagram


Pin 1 = shield (ground)   Pin 2 = White or Red (+ or 'hot')   Pin 3 = Black (-)

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Where can I learn more about Pro Audio?

Pro Audio covers a number of different system types, and even the way they are set up. For example, many of the same components and devices used to reinforce a live performance would be used in a recording studio. But the manner in which they are set up and used can be entirely different. The Sound Reinforcement Handbook has been in print since 1987, and can be found on our website. It contains a wealth of information on virtally all types of pro sound audio systems and how they are used. More of a reference source than a book to be read cover to cover, the information contained is still highly useful, even to those using state-of-the-art digital equipment. Commercial web sites and the internet in generaly are also excellent places to search for information.

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If I have 250W speakers, should I purchase a 250W amplifier?

Not necessarily, but it definitely depends upon the application. For a PA or sound reinforcement application, if you need to wring every last bit of sound pressure that a 250W speaker can provide (not recommended), you would go with a 500W amplifier. The thinking here is that a 500W amplifier could reach 250W without distorting or “clipping” the output signal. Such a distorted signal can quickly damage a speaker’s voice coil.

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What is meant by clipping?

Virtually any audio device will produce increased distortion if its input or output is over-driven. For example, if the input signal of an amplifier is sufficiently high, or the volume control adjusted too high, it can cause the output devices (transistors) to “saturate” and produce a badly distorted sound. This means that the peaks of the AC audio signal applied to the output transistors are causing them to turn all the way on. Just like pressing on the switch of a light that is already on won’t make the light any brighter, applying more drive signal to a transistor that is already saturated won’t make the music any louder.  When an amplifier’s output voltage cannot follow the peak of the input waveform, distortion occurs.

If the peak of the audio signal causes the transistors to saturate, the transistors are held fully on and passing direct current to the load until the peak passes and they begin to turn off. The reason this can be so damaging to a speaker is because the clipped signal, containing DC, represents twice as much power as the unclipped AC peak. In other words, 50 VDC delivered to a speaker represents twice the power as a 50VAC peak voltage. If the speaker is already near its power capability, clipping can easily burn the voice coil.

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Should a pro sound amp be operated with its controls set all the way up?

Never! All amplifiers provide a specific amount of “gain” from input to output. When an amplifier is used with the volume controls all the way up, then the gain of the amp is set to maximum, and the output level is controlled by the level of the input signal from the mixing console. In a sound system using microphones, such a setup can be a recipe for disaster should a microphone feed back through speaker system. Not only is this very annoying to an audience and the performers alike, it can damage speakers more quickly than you can reach the slider to turn it down.

In DJ systems, microphone feedback is not so much of an issue as the difference in the record level of various sources of audio. Many CDs, especially those produced recently, are recorded at as high a level as the format will permit. Playing such a CD after increasing the output of the console to play something with a lower record level can damage expensive speakers. Varying record levels among .mp3 files can create problems as well.

A properly adjusted amplifier can act as a limiter, so that no matter the level of the input from the console, the amp cannot damage a speaker. This can also be useful as one’s ears become desensitized after exposure to very loud audio.
 

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Parts and Accessories

Should a pro sound amp be operated with its controls set all the way up?

What is an inductor?

What is a transformer?

What is a capacitor?

What is a diode?

What is a resistor?

What is an LED?

What is a transistor?

What is a relay?

What is an inductor?

Inductors, also referred to as coils and chokes, are all synonyms for the same basic and very important device. Though used for a number of different purposes, all inductors are made from an insulated wire that is coiled or wound around some “core” material. Air is probably the most common core material, though laminated steel and ferrite are also common.

Coils are used in AC (alternating current) circuits due to the way that they respond to changes in current flow. Coils generally resist changes in current flow, whether that current is increasing or decreasing. The frequency of the AC current is also important. A coil of a given inductance may pass lower frequencies of AC power, but block higher frequencies from passing to the circuit’s load device by presenting a higher impedance.
 

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What is a transformer?

A transformer is a coil-based device that can change or “transform” AC electricity from a low voltage to a high voltage (step up), or high voltage to low voltage (step down). When the voltage is stepped up at the output of the transformer, the amount of current in the circuit is stepped down as compared to the original current supplied to the input. Conversely, if the input voltage is stepped down by the transformer, then the current available at the output is increased. This increase or decrease in voltage and current is always proportional to the change that the coil makes from input to output.

This voltage/current relationship in transformers also makes them very useful in circuits where the impedance (resistance to an AC voltage) of one device does not match the impedance of another device it needs to be used with. This means that the two devices are more or less incompatible. An example of this is when it is desired to use many speakers with one audio amplifier. A direct connection could damage the amplifier. But through transformers the many speakers could then be “seen” by the amplifier as a reasonable load. This is referred to as “impedance matching”.

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What is a capacitor?

The capacitor is another basic electronic component serving many purposes in electronic circuits. Physically, all capacitors are two “plates” separated by a very thin insulator called the “dielectric”. Each plate has a lead for connection into a circuit. The main specifications for a capacitor are its capacitance value, usually measured in micro-Farad (µF), and the maximum voltage it can withstand.

The capacitor behaves much like a coil in a circuit, though always in the opposite manner. Where a coil passes direct current and very low frequency, a capacitor blocks direct current entirely, but can pass alternating current if the frequency is sufficiently high. This would be a “filter” type application, which is just one of many that capacitors are used for.

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What is a diode?

A diode is an electronic device that will allow current to flow through it in one direction only. Commonly seen in rectifier circuits converting AC to DC, a diode’s main specifications are the “forward” current it can flow, and the PIV or Peak Inverse Voltage it can block. 

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What is a resistor?

A resistor is an electronic device that reduces current flow and voltage in the circuit into which it is placed. The main specifications of a resistor are its resistance value, measured in Ohms, and its power rating in Watts. All practical circuits must have resistance to current flow properly. With no resistance in a circuit, a “short circuit” is created which causes too much current to flow and the voltage to fall off. This usually results in the destruction of the voltage and current source (power supply). Other devices in the circuit may be damaged as well.

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What is an LED?

LED is an acronym for Light-Emitting Diode. It was noted in the 1920’s that diodes used in radio circuits gave off light during operation. The phenomenon is called “electroluminescence”, and is caused by electrons moving through the semiconductor material to eject photons, which makes up all visible light.

LEDs have been used for many years for indicator lights in many different applications and devices. They draw far less current than an incandescent light bulb, and are not generally subject to burn-out. Modern ultrabright LEDs are bright enough to work well in flashlights, and draw very little power from the batteries. This is mostly the result of their not wasting power in the creation of heat as incandescent lights do. The white hot filament in an incandescent light dissipates far more power as heat than light.

The internal structure of an LED is that of a diode, though they are engineered to shed as much light as possible, and have a transparent envelope to allow the light to escape. They are not intended for use in circuits where the voltage-blocking action of a standard diode would be needed.
 

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What is a transistor?

Internally, a transistor is actually two diodes. They are considered to be an “active” device as they have the ability to amplify (increase in power) an input voltage or AC signal.

A transistor can be thought of as a switch having no moving parts, which can be turned on a little or a lot. All transistors have three leads: base, collector, and emitter. An NPN transistor will begin to allow current to flow from the emitter to the collector with a positive voltage applied to the base that is about .7 volts more positive than the emitter. A PNP transistor flows current in the opposite direction with a negative “bias” on the base.

As the “drive” voltage to the base is increased, the current flowing emitter to collector will also increase. “Saturation” occurs when any increase in drive voltage causes no further increase in current flow from the collector. If it is an audio signal that causes the transistor to saturate, severe distortion of the output signal will occur.

Easily one of the most important inventions of the 20th Century, the transistor has affected every area of electronics. Most of the electronic devices we use and take for granted today would be impossible without them. As you probably already know, computers contain many millions of tiny transistors that when turned on represent a “1”, and turned off a “0”. The transistor replaced the vacuum tube as the amplifier in virtually all electronic applications, improving performance, efficiency, reliability, and reducing size and cost.

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What is a relay?

A relay is an electro-mechanical device that allows a small control voltage to switch a circuit carrying (high) power. A basic relay has four connections. Two of the connections are a switch, called a SPST or Single Pole, Single Throw switch.  When the relay is energized, a connection is made between the two terminals, which in turn complete an electrical circuit by allowing current to flow through the relay.

The remaining two terminals of the relay connect to a small coil of wire wrapped around a metal core. When DC voltage is applied to the coil (12 V is common), it becomes magnetized (an electro-magnet) and pulls an actuating arm that “toggles” the switch on. Removing the voltage from the coil releases the actuating arm from the electro-magnet and the switch re-opens.  

A common application for a relay is the headlights circuits in an automobile. It would require heavy-gauge wire and a large switch capable of carrying several amps of current mounted into the dashboard of the vehicle if this switch had to carry all of the power to all of the vehicle’s lights. Instead, a much smaller switch and very light wiring is used. The headlights switch energizes a relay to switch on the lights. Such a relay can often transfer 30 to 40 amps of current. A number of other circuits such as the starter motor are switched using relays.     

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Tools and Tech Aids

What is the best way to remove solder from a PCB?

What is the best technique to produce a reliable and consistent solder joint?

What is the difference in a soldering iron, gun, and station?

What is the best way to remove solder from a PCB?

Removing parts from a PCB generally requires that the solder be removed so the part can be freed from the board. As soon as the heat source is removed, the solder will solidify quickly, usually before the part can be grasped and pulled free. Two devices for removing melted solder from a connection are the desoldering pump and solder wick.

Desoldering pumps (solder sucker) can be either a small rubber bulb with a hard plastic tip, or a spring-loaded cylinder type. The spring-loaded type is the most popular. The pump is 'cocked', and when released, it creates a short but powerful vacuum at the tip. This vacuum action will pull melted solder off of the metal parts so they can then be easily removed. Desoldering pumps and bulbs clog easily as the solder often solidifies in the tip which restricts the vacuum action. They therefore require constant cleaning.

Solder wick works more slowly, but just as well as a pump. Solder wick is a fine copper braid, available in various widths. Wick is placed in contact with the solder joint and heated directly with the iron. When the wick and solder reach the melting temperature, the solder will flow into the braid of the wick by capillary action. For small connections such as IC pins, a narrow wick is best. Used on larger connectors, several inches of the wick may have to be used to 'wick' all of the solder from the connection. A wider wick would be called for here. The 'wicking' action works very well in removing solder, and can leave connections devoid of solder with a little practice. A difficult connection can sometimes have new solder added to it to aid in the start of wicking action. Solder wick has a shelf life as it does not work well if a layer of corrosion forms on it. Most quality solder wick products have an anti-corrosion coating to prevent this.

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What is the best technique to produce a reliable and consistent solder joint?

Soldering is not at all difficult to do, but it does take a little practice to get a consistent, reliable solder joint every time. Read more to learn how our experts do it.

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What is the difference in a soldering iron, gun, and station?

A soldering gun appears just as the name implies: like a gun. These devices are generally of a much higher wattage than a soldering iron. Soldering guns have a 'trigger' switch that causes the tip to heat when it is pressed and held. When it is put down, the trigger switch opens and the gun is then off. Though soldering guns heat rapidly, they are generally too hot for use on PCBs, light- gauge wire, and small semiconductor devices. They usually have a much broader tip making use difficult on solid-state PCBs. Guns work well on heavy gauge wire, such as 4 gauge or larger, because the large wire allows heat to sink away quickly from the area being soldered. The high output of the soldering gun is therefore required. A soldering iron cannot supply enough heat quickly enough to get the solder to flow into a large gauge wire. This will often result in a poor solder connection.

Soldering irons usually do not exceed about 35 watts. They are 'on' whenever plugged in, and should be returned to a soldering iron stand when not in actual use. A wide variety of tips are available for most professional irons, ranging from conical, screwdriver, chisel, and in different dimensions and heat ranges. 700° F tip is the most common.

Tips do wear out in time, and will need to be replaced occasionally. Using a namebrand iron such as Weller/Ungar, will ensure that you can find a replacement tip of the desired type when the time comes, and even a new heating element if needed.

Using an anti-seize compound on the new tip can make replacement much easier when the time comes. Due to corrosion, an old tip can be difficult to remove from the iron.

Cleaning the soldering iron tip is required occasionally to remove a buildup of burned flux. The buildup can act as an insulator making soldering difficult. Many soldering stands come with a small sponge which can be wet to wipe the tip. The problem is that the water rapidly cools the tip and the buildup then will not come off easily. A light sandpaper will remove buildup and clean the tip quickly, but can shorten the life of the tip if used vigorously. Tips are not expensive, so the tradeoff is not a big one.

Soldering stations generally provide a variable temperature adjustment for the iron, and some of the more sophisticated units will have a vacuum device for collecting melted solder. Some type of desoldering is generally required when removing and replacing soldered parts, especially from printed circuit boards.

Other types of irons include battery-powered units and gas/butane. These are preferable where commercial power is not available or inconvenient to access.

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Technical Support

Do you have technical help available?

Do you have a technical forum?

Do you have technical help available?

Yes.  We have an expert technical team available to provide free support on our products Monday - Friday 8AM-6PM ET and Saturday 9AM-2PM ET.  Email or call now for free advice on your projects or product questions.   

Email:  tech@parts-express.com

Call:  800-338-0531

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Do you have a technical forum?

An equalizer has stereo inputs and outputs, though most modern home stereo and home theater receivers do not have an 'EQ Loop' to accommodate them, in this case the 'Tape Out' is typically the best output to feed into the equalizer input. On those receivers that do have an EQ loop, simply connecting the equalizer and enabling the loop is all that is necessary to use it. Many graphic equalizers intended for home audio do have multiple inputs so that the various audio devices (cassette, CD, DVD, etc.) can be connected directly to the equalizer rather than to the receiver. This allows the user to select between audio sources without changing cabling. 

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Amplifiers

What is Power RMS?

What is Harmonic Distortion?

What is meant by clipping?

What does an amplifier do?

What is Peak Power?

What does RMS mean?

How is amplifier power measured?

What is dynamic range?

What is headroom?

Whole-House Audio

Can I control a whole-house system from other locations in the house?

Can I listen to different sources of audio in different rooms?

Can I use my home stereo or home theater receiver for whole-house audio?

How many speakers can I connect throughout my house?

What is a whole-house audio system?

What type of speakers are commonly used in whole-house audio systems?

What are some of the components needed for a whole-house system?

What type of speaker wire is used in whole-house audio systems?

What type of speaker wire is used in whole-house audio systems?

What type of speaker wire is used in whole-house audio systems?

What is Power RMS?

There is no such thing. Yes, the term is commonly used to describe the power capability of a speaker or the output power of an amplifier, but it is a misnomer. Voltage RMS times Current RMS do not equal Power RMS, it provides a “continuous average power”. Also, the voltages and currents present in audio amplifiers from the complex audio waveforms share all kinds of phase relationships, meaning that they are often as not in time with each other, complicating the issue further. So calculating power from instantaneous samples taken over a period of time would be the only way to do it, and would result in an “average continuous” power, not Power RMS.

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What is Harmonic Distortion?

Distortion is any unwanted change in an audio signal, and there are many types. The type most commonly discussed is harmonic distortion. For example, if a 100 Hz tone (sine wave) were input into a circuit, the output will contain not only 100 Hz, but also 200, 300, 400, and 500 Hz as well. This output can be said to have 2nd, 3rd, 4th, and 5th harmonics. Since they were not part of the original signal, they are considered distortion. Each subsequent harmonic is usually, but not always, lower in amplitude than the one before it.   

The distortion content can be described as being so many dB below the signal, or as a percentage of that signal. It can be specified for individual harmonics, or as a composite value of all. The latter is the most common, and is referred to as Total Harmonic Distortion (THD). This is often done at either 1 KHz @ 1 Watt (most common), or 20Hz to 20 KHz @ full rated power. The former would be representative of what most people would hear in daily use of a home receiver, the latter what someone using a pro sound power amplifier would be most interested in.

The human ear can detect harmonic distortion as low as .3%. However, with low order harmonics the threshold is near 1%. Virtually every part of a sound system creates its own part of THD.

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What is meant by clipping?

Virtually any audio device will produce increased distortion if its input or output is over-driven. For example, if the input signal of an amplifier is sufficiently high, or the volume control adjusted too high, it can cause the output devices (transistors) to “saturate” and produce a badly distorted sound. This means that the peaks of the AC audio signal applied to the output transistors are causing them to turn all the way on. Just like pressing on the switch of a light that is already on won’t make the light any brighter, applying more drive signal to a transistor that is already saturated won’t make the music any louder.  When an amplifier’s output voltage cannot follow the peak of the input waveform, distortion occurs.

If the peak of the audio signal causes the transistors to saturate, the transistors are held fully on and passing direct current to the load until the peak passes and they begin to turn off. The reason this can be so damaging to a speaker is because the clipped signal, containing DC, represents twice as much power as the unclipped AC peak. In other words, 50 VDC delivered to a speaker represents twice the power as a 50 VAC peak voltage. If the speaker is already near its power capability, clipping can easily burn the voice coil.

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What does an amplifier do?

In a nutshell, an audio amplifier increases the voltage and current gain of an audio signal so that it can drive a speaker. Speakers are notoriously inefficient, dissipating (wasting) most of the input power as heat and through other losses. So the comparatively small “line level” signal coming from your CD or DVD player cannot directly drive a speaker to a useable level.

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What is Peak Power?

Peak power is an ill-defined method of evaluating the power output capability of an amplifier. These numbers are often greatly inflated as compared to average continuous power, and seem to carry no value other than for a company to advertise a higher power capability. Be suspicious anytime that an amp is simply rated as “500 Watts” or “1000 Watts'. Stated as such with no other information, it is not a meaningful number.

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What does RMS mean?

RMS stands for “root-mean-square”, and is the means by which an effective value for AC calculated. In other words, it is used to calculate the work an AC (alternating current) voltage can do as compared to a DC voltage. Calculating the power being transferred in a DC circuit is straightforward: multiply the voltage times the current (in amperes). For example, if a device draws 2 amps from a 12 volt battery, it is pulling 24 Watts of power from the battery. 2A x 12V = 24W.

But with an AC voltage, it’s not so simple because the voltage is rising to a peak, falling back to zero, and then does the same thing in the opposite polarity. Because the AC voltage stays at peak for just a very short time and then falls back to zero,  the work that the voltage can do is somewhat less than the “peak” voltage. Mathematically, if you multiply the peak voltage of an AC power source by .707, you will derive the voltage RMS. For example, the AC voltage in a wall outlet peaks at about 170 VAC. Multiplied by .707, you get 120 VAC RMS. This means that 120 VAC RMS will do the same work as 120 VDC.

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How is amplifier power measured?

There are two basic methods, one is “FTC”, and the other is “EIA”. Very similar, both methods entail connecting the amplifier to a load device (usually a large power resistor), driving the amp to the onset of clipping, and then calculating the average continuous power output based upon the AC voltage dropped across the load impedance. 

The FTC stipulates an input signal of 1KHz. The EIA method is more involved, requiring the amp to be fully warmed up, drive loads at different frequencies for which it is rated, to be able to run indefinitely at full power without shutting down, and so on.  The EIA method is more commonly used on pro sound amplifiers such as a band or concert venue would employ.

Instantaneous amplifier power may be measured at the speaker terminals using a multimeter set to VAC connected in parallel (+ to +, - to -) . To determine power, multiply this number by itself (square it), and divide by the rated resistance of the connected speaker. For example, if you read 20 VAC at the terminals of 8 ohm speakers, the equation is 20^2/8, which is 400/8 or 50 watts.

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What is dynamic range?

The dynamic range of an audio signal is the difference in intensity between the loudest and the quietest sounds. It is measured in decibels.  

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What is headroom?

A common error made in running a sound reinforcement system is to operate the system too close to its maximum power output. This happens for two main reasons: 1) the PA system is inadequate for the size of the venue, and/or 2) the person running the system feels no SPL level is too high.

Audio, whether it is the spoken word or music, consists of constantly varying intensities of an infinite variety of possible sounds.  To prevent clipping and the resultant distortion, the sound system must be able to reproduce the portion of the audio program having the greatest intensity without causing clipping or distortion. Adjusting the system as such, is providing the amplifier with sufficient  ”headroom”  to be able to reach all transient peaks in the program material without clipping.

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Whole-House Audio

Can I connect outdoor speakers to a whole-house system

Outdoor speakers are commonly a part of a whole-house system. They of course need to be of an outdoor type if they are to be left outside. The most popular are “rock” speakers, which are completely weather resistant and available in several different versions and sizes. “Patio” speakers are also very popular. They are generally about half the size of a shoe box, and mount under a soffit or similar location. Outdoor-rated volume controls are available, as is speaker wire. Such speaker wire is called “direct burial”, and should be used for all outdoor applications whether the speaker wire is to actually be buried in the ground or not. 

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Can I control a whole-house system from other locations in the house?

Remote control of a whole-house audio system is usually done through an IR (infra-red) repeater system. These can be stand-alone systems, or can be part of the impedance matching volume control by mounting the IR target into the wall plate. There are also systems that can allow any IR remote to transmit the code via radio signal back to a receiving unit.

Regardless of the type system, all capture the IR code from the remote control, and transfer it to IR flashers that are attached to the IR windows of each device to be controlled remotely. All components having an IR flasher attached will receive all codes received into the repeater system. Only the device that recognizes the code will respond. One system can support many IR targets, which can be located about any where in the home. 

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Can I listen to different sources of audio in different rooms?

This is not an uncommon feature, but does require a much more sophisticated audio system. For a set of speakers in one zone to play a variety of input sources, it must have its own dedicated amplifier. These systems are set up in two common configurations.

The first is a unit containing 4, 6, or even 8 or more stereo amplifiers. In-wall zone controls are usually connected back to the main unit via a CAT-5 data cable, which allows the user to change the source of audio, and also control the volume of the speakers. Many will also allow the use of an IR remote control through the system to control connected components such as CD players, AM/FM receivers, etc. Other systems may even be controlled through a PC or laptop computer.

The second common type is called 'A-Bus', in which the wall plate controller actually contains the audio amplifier for the room or zone. Also connected back to a main unit via CAT-5 data cable, these systems often have inputs on the wall plate control for iPod, mp3, or other portable audio player for that and sometimes other zones. Features and price point vary greatly on these systems, and some will require the services of an authorized installer.

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Can I use my home stereo or home theater receiver for whole-house audio?

It is best that you don’t. Most impedance-matching volume controls and selector boxes use transformer-based protection circuitry. Home audio receivers do not have a power amplifier that is robust enough so as not to be negatively affected by what is referred to as a highly “reactive” load. Even when properly installed and adjusted, many receivers will run very warm, and may even go into protection mode as a nuisance. Some receivers may even be damaged, depending upon what protection circuits were built into them.

A common scheme is to use the home receiver as the source of audio, and use its line level outputs (tape line out or auxiliary line out) as the audio source for a two-channel power amplifier that was intended for use in sound reinforcement systems. Such amplifiers are commonly available at a lower price point than many home receivers, and can handle up to 16 of the impedance matching volume controls.

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How many speakers can I connect throughout my house?

Directly connecting a second pair of standard 8-ohm speakers to an average home stereo receiver may exceed its recommended load capability. So it should stand to reason that some means of ensuring a practical load on an amplifier driving many speakers would be a necessity. The device used to distribute the power amplifier’s output while maintaining a reasonable load will dictate how many speakers can be connected to a given amplifier. This is referred to as impedance matching the amplifier to the speaker system.

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What is a whole-house audio system?

A whole-house audio system, as the name implies, allows you to enjoy your stereo audio system from about anywhere in or around your home. These systems vary greatly in features, capability, complexity, and cost. They can range from a system you can install yourself to something best left for a professional to install and set up. 

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What type of speakers are commonly used in whole-house audio systems?

The most common speakers used in whole-house audio systems are in-wall or in-ceiling types. They are designed to be easily mounted directly into a sheet rock (dry wall) ceiling or wall. In-wall speakers are generally rectangular in shape, ceiling speakers are round. They come with a cut-out template so the correct size opening can be accurately cut into the wall or ceiling. They generally require no other brackets or hardware to be securely mounted into a wall or ceiling. Most have a plastic frame and metal grill which can be painted with any latex interior house paint.

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What are some of the components needed for a whole-house system?

Maintaining a reasonable load on the amplifier is of utmost importance in such an audio system. There are two devices commonly used to accomplish this in a whole-house system: impedance-matching distribution panels, and impedance-matching volume controls.

The volume controls are the most popular as most people like being able to turn speakers up, down, or off at the speaker location, rather than having to go to the audio system to make adjustments. The volume controls have impedance settings you adjust at the time of installation, based upon the number of volume controls (or stereo speaker pairs) connected to the amplifier.

Speaker wire distribution boxes and panels can take several different forms, and may or may not have impedance matching. Some table-top units can accommodate two sources of audio input. Each zone would then have an input selector switch, and some units even a volume control for that zone. Speaker wire distribution panels are also available built into Decora-style inserts and covers. These can mount to a standard single or double gang junction box or mounting bracket (mud ring). The room side of the plate will contain binding posts for connection of the left and right channel speaker wires from the amplifier. The back side of the plate will have speaker wire connectors for 4 or more pair of speakers. From here, the speaker wires would usually go to the impedance matching volume control.

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What type of speaker wire is used in whole-house audio systems?

Installation or architectural speaker wire is often used for a couple reasons. First, if the installation must withstand an electrical code inspection, an installation type wire is usually required as it is UL approved and will have the required CL3 fire rating. Also, if the wire has to be pulled through walls, around joists and corners, the smooth PVC outer jacket on the installation cable makes the job much easier. In addition, it is much less likely that installation cable would be stretched or otherwise damaged during pulling.

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