Vifa Impedance Measurement.

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I began measuring the impedance response of some drivers for a speaker project I am working on for a friend. I am using Audua Speaker Workshop. I have found the software to be very good (considering it is free it is excellent - see

The tweeter I am using is the D27TG-45-06 from Vifa. I was surprised to see the impedance response looked quite different from that on the data sheet. The datasheet peaks at 650 Hz as suggested by the resonance figure. The value at this frequency is about 12 ohms.
My measurement however peaks at about 950Hz - 9.7 ohms.

I would really like to hear any reasons anyone can think of for this difference.

The data sheet measurement is done on an infinite baffle while mine is done in the cabinent - 250 mm wide.

Also Speaker Workshop measure the voltage drop across a resistor connected in series with the driver. Could this resistor (11 ohms) be affecting it?

Also has anyone else tried building a measurement mic with panasonic mic capsules?

You should know by now that manufacturers specs are liable to change from what they were originally listed. Batch to batch deviations, quality control etc. Even if a 1 inch dome tweeter has a 950Hz resonance, doesn't make it any worse than 650Hz. The low impedance at resonsnce indicates that it has ferro fluid and is well damped. Fs will change with temperature and break in.
Thanks for the reply - I think the software is good but I would have thought Vifa would get thier measurements a bit more accurate.

Any other ideas? - could the baffle size be affecting it? Or is it really just manufacturing tolerance?

The drivers are very well run in - I am actually
re-designing the crossover.
Unfortunately it's not uncommon that tweeters differs quite much from data sheet speces.

The worst I have seen was a tweeter from Seas that was specified to 550Hz and measured to 1850 Hz.
During testing there was severe mecanical distortion because the coil scraped against the pole piece.

Vifa or Seas tweeters ? Thanks, but not for me.

Tweeters in Vifa and Seas price range ?

Unfortunately they are the best I have found in that price range. Peerless tweeters is not as good as tht best from Vifa or Seas.

Peerless woofers are great. Their specifications make them very suitable for the intended use, no matter if it is for bass reflex or closed boxes. Vifa's woofers is mostly somewhere in between. Too fat bass in bass reflex boxes and to thin in closed box.

But I have questions about Peerless woofers too.
I intended to use a 8" woofer for a 3-way project and they differed quite much from the data sheet specifications, so I called Peerless and asked why, and they answered that they got stronger magnets the last delivery, and that they where going to be like that in the future.

However, I'm using a 10" Vifa bass myself, but in a slave bass configuration where it performs extremely well.
So it depends very much on what you do with the woofer, but generally I haven't been able to get a really good result with Vifa woofers in "black book" bass reflex or closed boxes.

Generally I think it is worth the money to take a step up regarding the tweeters to Scanspeak, Focal or maybe Thiel & Partner.

Thanks for the replies.

I am really surprised that the specs could change that much.
You really do have to measure your drivers before designing the crossover. How do large speaker manufactures deal with this issue? They must be changing crossover parts each time they get a new batch of drivers in.
I am not sure - maybe the producers remeasure a couple of drivers from each batch.

I would certianly measure drivers before designing the crossovers from now on.

Has anyone tried building the Mitey Mike with the Panasonic Mic capsules? If so what sort of results have you got from it?
Speaker manufacturers match speaker pairs on varying degrees, which is often reflected in price. Some speaker manufacturers which have custom drivers produced for them, often use drivers that were picked selectively and made in much smaller quantities, so quality control is of the highest regard. Rarely, however, is the crossover of each individual pair of speakers factory modified.
When Rogers used to get in a batch of KEFs, they'd measure each and every one. Then, depending on the individual driver, they'd change connections in the LS3/5A crossover (the crossover had several adjustments designed in) to match the driver. If you popped a driver, you had to send in the serial numbers so they could send a driver that would match your crossover settings. Conversely, you could send in the speakers (not a problem with something as small as the LS3/5A) and they would put in a matched pair, resetting the crossover.
Yeah, if you're aiming for high end performance, you'll find driver tolerances frustrating.

diyAudio Moderator Emeritus
Joined 2001
One thing about variation on woofer specs. I think we should differentiate between variation from printed specs and specs which will make a difference when the woofer is placed in a box.

If a speaker's Vas is 25 percent larger than it's printed spec, but it's Fs is a quarter of an octave lower, then that speaker will essentially perform in a box the same as if the printed specs were met. In a ported box, we might have to adjust the Fb a little, but still.

Hedlund-do you recall if the variation from printed specs on that Peerless woofer really affected the performance of the speaker/box combination?

[Edited by kelticwizard on 11-28-2001 at 07:08 PM]
My experience suggests that some manufacturers actually do match drivers. I had to check some AR woofers (4 of them) that were supposedly match, (HA, as if). Well knock me done with a feather, they were all identical, Fs +-0.5Hz, even though they were all sightly off spec by a couple of Hz. I have tried the same with a batch of 8 Peerless 12" drivers and got a variance of 3Hz, personally I wouldn't go adjusting the crossover, I don't believe I could hear the difference. I have in the past noted great variation from the specs, I would recommend that you always test the driver first!

Regarding the tweeters, on Janne's suggestion I compared the Peerless, Vifa, Focal and Scanspeak tweeters, (I couldn't get some Thiel & Partners). I found that I liked the Scanspeak units best, (you'll notice I didn't say that they were better). But for the price of the Peerless tweeters, (nearly 1/10th the Scanspeaks) they put in a good show, so I would recommend to anyone to try them, just not in your penultimate system. I'm now using both in different systems. Selection must be a personal one, Janne seams to like metal domes I prefer soft, (possibly because that's what I'm used to), who's right? I think we both are, (but then I'm biased:)).

Regards WALKER

Sorry to say it, but I have no preference for eigther soft domes or metal domes, just the best sound possible.
The tweeters I have recommended don't suffer from "metal dome syndrome" which is carachterized of sharp treble that you almost can cut cheese with. They are very clear and free from distortion.
But both types have always some small problems.
Thats why I use a pair of upgraded Apogee Stage (ribbons)for midrange and treble in my reference system.
No boxes and light drivers have been the ticken to my audio nirvana.


Yes it clearly effected the box design.
When designing a bass reflex system I like a Rf/Qes ratio of around 95 which the Peerless driver alost perfectly matched with data sheet speces of Rf=33 Hz and Qes=0.35.
When measuring them I got (if I remember right) around Rf=36 and Qes=0.3 which give a ratio of 120.
Normally, if Rf gets higher Qes gets lower and vice versa but when both increases your out of business.



Yes, ribbons can be a pain in the *** too.
The sound I get from Apogees Signature tweeter ribbons is very good ideed. Specially with a good tube amplifier.
I had a pair of monoblocs (Spark 850, 50 watt class A with four 300B in push-pull) until a couple of months ago and I already miss them.

I think I'm seeing a common thread there, I never had the ribbons on a valve amp. Tried them with an early Hitachi design MOSFET and some Yamaha BJT power amps, they sounded nice buuut. I used them for 5 years, they just didn't take me there, a lot of the time. Sold them, just knew I'd regret it some day. I'd love to try them on tubes now.

Spent some time listening to Magnepans, if brass is is your bag nothing comes close, spectacular on the ivories as well. Trouble is they wouldn't do Floyd when I'm in the mood.

Regards WALKER

[Edited by walker on 11-29-2001 at 12:03 AM]
Please note that I'm only using the woofer panels and the ribbon tweeters out of my old pair of Tympani IVs. I've replaced the midranges with BG RD-75s, and have added rather, um, extreme subs. Everything's quad-amped.
They'll do Floyd...and the 1812 Overture, with ease.

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