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Vifa BC25SC06-04 1" Textile Dome Tweeter
Using as a replacement tweeter for a PSB Image 6T
As seems to be a common complaint, one of the tweeters in my now 10 year old PSB Image 6Ts appears to have blown. I understand that these VIFA tweeters are a good fit as a replacement. I also understand that the SPL of the VIFAs is about 5 db or so higher than the stock PSB tweeters, and the DB resistance is 1.7 lower than the stock PSBs.I am new to this tweaking, but I want to make sure I understand what needs to be done to make the VIFA as close to the original in terms of SPL and crossover as possible. If I install a 1.8 ohm resistor in series, will that both bring the crossover back to near original level AND attenuate the SPL back to near original, or would I need both a resistor and an L-Pad?If an L-pad is needed, how do you set the spl -- just based on your ear? Also, where does the L-pad go -- inside the cabinet?I'm sorry if this question is repetitive of others, but I was just hoping for some clarification.Thanks.
There are a few ways to go about this.Series Resistor:If you add a series resistor of 1.7 ohms you will will bring the series resistance close to what the original part has. However, this does not guarantee that the impedance will match that of the original tweeter. It will also only reduce the output of the tweeter by 3.2db. So, this is not sufficient.L-pad + Series resistor:As you suggested you could use a series resistor, and then use a pre-made l-pad. This will help reduce the volume and maintain a constant impedance. However, since the tweeter you are trying to mimic has an impedance of 6 ohms (remember impedance =/= DC resistance), no l-pads here will work as they are intended for an 8 ohm speaker (or 16 ohm) and will throw off the impedance you are trying to fix, and thus change the crossover point. You do indeed use the dial to level match the tweeter by ear. This option is also unsuitable for your case.Make your own fixed value offset l-pad:The best option is to make your own l-pad that includes an impedance offset. This is not hard and only involves two resistors. According to Jeff Bagby's wonderful Passive Crossover Designer the following l-pad will bring the overall impedance to about 6 ohms.Rs= 2.7 ohmsRp= 22 ohmsBasically you wire the 2.7 ohm resistor in series with the tweeter and the 22 ohm in parallel to it, after the crossover.See the diagram below for the layout and the items I selected for the parts.This will reduce the output of the tweeter by 5.09 db and bring the perceived impedance of the tweeter to 6.08 ohms
Date published: 2014-02-12
Attentuate tweeter level
I installed these in a pair of PSB Image 4T speakers. The speakers are rated at about 91db at 2.83V/1M. The tweeters are rated at about 96db. The tweeters sound good but seem too loud. What is an easy/inexpensive fix to drop the level about 5db?
Add an L-Pad if you don't want to change the frequency cut off of the crossover.Desired cut = -5 dBR Driver = 4 ohmR Series = 1.75 ohmR Parallel = 5.14 ohmHowever, it seems that others report that the original PSB tweeter had a higher DC resistance, and nominal impedance (6 ohms vs. 4 ohms). So, in changing out he tweeter you have drastically lowered the high pass frequency of the stock crossover already.So, if you want to maintain (kind of) the same level of response, and attenuate the tweeter 5db you should a series resistor in addition to an Lpad.Desired cut = -5 dBR Driver = 4 ohmR Series = 2.63 ohmR Parallel = 7.71 ohmthen add in aR Series = 2 ohmafter the Lpad.So, in the end you have an apparent impedance of 6 ohms on your high pass section and you have an attenuation of 5db.You could probably get away withDesired cut = -5 dBR Driver = 4 ohmR Series = 4.63 ohmR Parallel = 7.71 ohmand achieve the same results, but I have never done it that way.
Date published: 2014-02-12
Can the heatsinks be removed from the magnet?
If so, is there a drastic loss in power handling? Only gonna be putting up 25w RMS max, and crossed at or above 6k.Depth is my concern. How tall are the heatsinks?Thanks.
Have at it. The heatsinks are probably half an inch tall, and I think they are largely unnecessary. These things are pretty efficient and won't generate much heat.
Date published: 2012-01-20
spl output, 93.9db freq. graph, or 96db spec. sheet?
specs state 96db spl output, but the freq. graph shows 93.9db spl output. which one is correct?
The output of the tweeter is 93.9 dB at 1w/1m and 96 dB at 2.83V/1m. 2.83V into 4 ohms is two watts, thus the 3 dB increase.
Date published: 2012-06-11
Safe to xover @ 2500 khz instead of 3000 khz?
all at 12 db slope; would 500 hz make a huge difference?, the issue is i cant find a 4 ohm @ 3000 khz crossoverthx
2500 is fine at 12db/oct. Another option is a 6db/oct at 3K which would be safe.
Date published: 2012-07-10
Wiring method to achieve final load of 8 ohms
I am planning on using this tweeter with two full range drivers. However, the full range drivers are rated at 8 ohms, and I need a final load of 8 ohm. I believe I can do this by wiring the two full range drivers in parallel to achieve a 4 ohm load, and wire the tweeter in series with the drivers to achieve an 8 ohm load. So, something like L1= (8*8/16) =4, L2= (L1+L2) = (4+4) =8 ......Any feedback on possible performance issues or other caveats would be greatly appreciated.Thanks…
Xovers don't work that way. If you have a xover, and are not running the FR's wide-open, then their impedances are static to either side ofthe xover point. They really won't interfere with each other if done properly. You have an 8 ohm mid and 4 ohm tweeter = 4 ohms above and 8 ohms below xover in this manner.So- you only want a single 8 ohm midbass to keep your load reasonable. If you run this wide-open without any electrical compensation or xover, the inductive rise may be enough that the 2 in parallel above the frequency of xover for the tweeter will still yield an approximate 8 ohm load in the end. If the FR unit has a flat impedance (or low Le# and is run wide-open, then you may run into issues with ANY tweeter run off a conventional xover.Best results as super-tweeter should be to use approximately a 0.22-0.47uF cap on the tweeter, and padd it down enough to match with a series resistor only. If it is a large enough value resistor, then your impedance concerns will be moot. Wire the tweeter in with:Amp#+#---resistor---cap---tweeter#+#Amp#-#----tweeter #-#If the resistor is at least a 10 ohm, I think you'll be okay.
Date published: 2013-01-16