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Old 28th November 2001, 06:35 AM   #1
Dave is offline Dave  New Zealand
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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 http://www.audua.com).

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?


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Old 28th November 2001, 06:58 AM   #2
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Default I CAN'T COMMENT ABOUT YOUR SOFTWARE,

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.
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Old 28th November 2001, 07:14 AM   #3
Dave is offline Dave  New Zealand
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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.

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Old 28th November 2001, 12:10 PM   #4
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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.

Janne
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Old 28th November 2001, 02:43 PM   #5
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Hedlund:

What would be your recommendation for a tweeter in Vifa and Seas price range? Also, what do you think of Peerless tweeters, (some people have said that Peerless woofers are fine, but Vifa makes a better tweeter)?
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Old 28th November 2001, 03:41 PM   #6
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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.

Janne
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Old 28th November 2001, 08:01 PM   #7
Dave is offline Dave  New Zealand
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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.

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Old 28th November 2001, 08:50 PM   #8
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Dave,

do you think they send drivers with different specifications from batch to batch to the loudspeaker producers ???

Janne
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Old 28th November 2001, 09:29 PM   #9
Dave is offline Dave  New Zealand
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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?
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Old 28th November 2001, 10:28 PM   #10
Super is offline Super  United States
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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.
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