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| Design Goals | Driver Selection | Enclosure Design | Enclosure Assembly | System Adjustments | Conclusion | Parts List | | ||||
| Driver Selection | |||||||
| I selected the Dayton RSS12HF-4 because it is one of the most popular subwoofers we offer, and the 12" cone is a desirable size for producing adequate bass for home theater systems while being musical enough for stereo playback. With proper loading and amplification it will meet virtually any reasonable expectation in terms of sound quality and low frequency output. It features three short circuit paths, an extensive vented motor structure, and a 2-layer coil for reduced back EMF. |
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| Enclosure Design | |||||||
| The new enclosures for this design are more complicated than any I've yet built. Each speaker utilizes two separate enclosures, like the originals, but in this case they are actually separated from each other. The upper MTM cabinet is simply a vented bookshelf speaker that is separated from the lower cabinet by using two 3" diameter PVC tubes that are 1-1/2" long and bolted through the center. I thought I would go all out and try to time-align everything, so the woofers use a 1-1/2" baffle, where as the tweeter is set back 3/4"
My main goal in this new design was to measure the woofers I had, and build the perfect-sized enclosure for them. In this case, it was about 2.1 cu. ft. after subtracting driver displacement. An 11" long 3" diameter port would yield an F3 of about 37 Hz. This was originally going to be a typical rectangular prism with double-thick walls, until I remembered a design that Zaph had used for a couple of wall-mount Aura speakers he built. He used a wood bending technique that I thought was very cool and not too difficult to try, so I drew a curved-wall design in AutoCAD. The curved-wall version looks better, and also helps to make the cabinet stronger-doublethick walls are no longer required. The top and bottom plates would be double-thick however, and there's also extensive internal bracing. The finished result is a woofer cabinet that weighs close to 50 lbs. empty, and has almost no wall resonance. |
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| Enclosure Assembly | ||
| The enclosure is constructed of precision CNC cut 3/4" MDF then assembled with polyurethane glue for superior strength. An internal brace is also utilized to minimize cabinet resonances. The enclosure is pre-drilled and cut for the amplifier,driver, and spikes, so after some assembly (an hour or so), this is essentially a plug-n-play system. The easy assembly went as follows: cut and apply 2-1/2" foam to all internal panels, mount the amplifier, connect and mount the driver, and insert spikes. |
| System Adjustments | |||||
I took nearfield measurements, which is standard practice to properly measure subwoofers, to help negate room reflections. I was looking for the lowest f3 with the flattest frequency response. I first wanted to get a starting point (reference) so I measured the response of the driver-amp system with the crossover setting at maximum and no equalization. Looking at the graph below the f3 was around 40Hz. A little known but useful feature of the Dayton HP (high power) amplifiers is the 6 dB notch filter, which was added for the Titanic kits to help flatten their frequency response. Next I measured the system output after adjusting the amplifier settings to create the lowest f3 and flattest response curve, with the notch filter disabled (Red). I achieved a relatively flat response with an f3 of 30 Hz. I noticed a peak in the 50-60 Hz range and because of this peak I thought the complete system might also benefit by enabling the notch filter. I measured again with the notch filter enabled and after some tweaking was able to achieve a relatively flat response with an f3 of 25 Hz (Blue). Red Response - Output of the amp-driver combination with notch filter disabled, crossover set at 100 Hz, and with parametric EQ settings of: Frequency = 25 Hz Bandwidth = 0.20 Level = +6 dB Blue Response - Output of the amp-driver combination with notch filter enabled, crossover set at 85 Hz, and with parametric EQ settings of: Frequency = 25 Hz Bandwidth = 0.27 Level = +6 dB Note: To compare measurements of notch fi lter enabling vs. disabling, I found it easier to remove the rear enclosure from the amp and mount it separately in the cabinet. This allows easy access to the jumper while maintaining the integrity of the cabinet for measurements. The choice is yours, to notch, or not to notch. With plenty of power available, I feel the tradeoff of a little efficiency for a lower f3 is worth it, so my choice is with the notch filter activated. Note: The default factory setting of the notch filter is "disabled". To enable the notch filter, simply switch the position of this jumper (connect left and middle pins.) Here are the measurements of the amplifier's output with the notch filter enabled (Blue) and disabled (Red). |
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| Conclusion | ||
| This subwoofer system produces tight, clean bass from any source. Adjustments to volume, crossover frequency, bandwidth, and more, are easily accessible via panel controls. The amplifier along with a high-excursion, low-distortion driver and a solid MDF cabinet, will ensure clean, detailed bass, even when you crank up the volume. |
| Parts List |
Part # |
Description |
Qty |
| 295-464 | Dayton RSS315HF-4 12" Reference HF Subwoofer | 1 |
| 300-806 | Dayton HPSA500 500W Subwoofer Amplifier | 1 |
| 302-812 | Dayton SWC-2CO 2.0 cu. ft. Subwoofer Cabinet w/Cutouts | 1 |
| 240-715 | Dayton DSS4-BC Black Chrome Speaker Spike Set, 4 Pcs. | 1 |
| 260-776 | Cast Frame #10-32 Speaker Mounting Kit | 1 |
| 260-515 | Acoustic Foam 2-1/2" 24" x 18" (UL 94) | 3 |
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