Has anyone measuered Fs for a Vifa P13? - diyAudio
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Old 13th December 2009, 08:02 AM   #1
SBob is offline SBob  Sweden
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Default Has anyone measuered Fs for a Vifa P13?

Hi,

I have a Vifa P13WH that I bought a couple of years ago. I am now planning to build a centre speaker with it so I have started measuring it.

The problem is, I keep getting an Fs of 100-110 Hz, both with Speaker workshop (i.e. sound card) and a signal generator with the method from "Testing loudspeakers" by Joseph D'Appolito. Since the manufacturer lists the Fs as 60 Hz I am now wondering if anyone else has measured their P13s and has gotten similar results? Is my unit faulty? Or is it normal with this deviation from the listed specs?

I have tried to break it in for a couple of hours. No change in Fs.

The Vifa P13 was a very popular speaker, so I thought that maybe someone here has experience with it. I would really appreciate it if you would share your insights, before I build a cabinet for a defect speaker...
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Old 13th December 2009, 09:29 AM   #2
gornir is offline gornir  Sweden
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Hi,

Yes I have. Here are my results with WT3.

Vifa_P13WH-00-08
Vifa No1 No2 No3 No4 Average
DC Re 5,7 5,774 5,89 5,943 5,652 5,81
Le 0,7 0,3976 0,4015 0,399 0,3946 0,40
fs 60 98,25 98,25 98,25 98,25 98,25
Qms 1,38 1,451 1,406 1,404 1,498 1,44
Qes 0,43 0,7313 0,7275 0,7296 0,6975 0,72
Qts 0,33 0,4863 0,4794 0,4801 0,4759 0,48
Bl 6 6,095 6,172 5,974 5,959 6,05
Rms
Mms 7,5 7,622 7,622 7,098 7,098 7,36
Cms
D cm 10,46 10,46 10,46 10,46 10,46 10,46
Sd cm2 86 86 86 86 86 86,00
Vas 10 3,57 3,57 3,834 3,834 3,70
Spl 88 88,55 88,57 88,87 89,06 88,76


In my opinion the P13 is more like a midrange than a woofer, but for center channel duty it would be ok.
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Old 13th December 2009, 09:50 AM   #3
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Have you made an impedance jig? Speaker workshop can measure the impedance directly with an appropriate jig, and I've found it very good for this (provided you have the drive levels low, and calibrate everything properly).

Which method did you use in Joe D'appolitos book? I seem to remember a similar problem posted recently, I think the answer is that it is not normal for the FS to be out by as much as what you have measured.

There are two possibilities that I can think of. One is your woofers are out of spec, the second is that your measurements are faulty

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Old 13th December 2009, 10:09 AM   #4
SBob is offline SBob  Sweden
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For Speaker Workshop I use a version of the Wallin jig and it has worked on earlier occasions.

I used the voltage divider method from D'Appolito. However, I cannot get the "control" fs to work, the one called fs'. fs' is about 15 Hz lower.

Maybe I should try a third method, but I guess it looks like the woofer is out of spec Too bad they don't make them any more. Any ideas on what can cause them to be out of spec? Is it common? I have built a number of speakers and I have never had this problem before...

Robert
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Old 13th December 2009, 10:35 AM   #5
gornir is offline gornir  Sweden
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Hi,

Yes, I have measured 4 of them with WT3 and all of them have a FS around 100Hz. In my opinion P13 is more like a midrange than a woofer.

/Goran
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Old 13th December 2009, 12:01 PM   #6
SBob is offline SBob  Sweden
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Thanks Goran, it seems that my unit is not unique. I have measured a little more with Speaker workshop and got the following parameters:
Fs = 101 Hz
Vas = 3.8 l
Qts = 0.396

Which is very similar to your four units. Still, I find it odd that they are so much off. Maybe they are bought in the same place and are from the same batch (Hifikit)? Or maybe there is a reason there were discontinued.

I am thinking of getting another woofer for my centre speaker, I would like it to go down to at least 80 Hz since that is the cut-off frequency my amplifier uses. The reason I choose the P13 is that I have P17s in the front speakers. Any suggestions on a similar woofer that I can use? Or is 100 Hz OK for a centre speaker even though the amp cuts off at 80Hz?

Robert
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Old 13th December 2009, 01:33 PM   #7
gornir is offline gornir  Sweden
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Hi,

I bought mine second hand for a very good price, 50kr/each. I don't know if they are from Hifikit originally, but it's likely. Perhaps the surround has stiffened with age or Vifa suddenly decided to change the specs? I will try to use mine in a MTMW configuration as midrange together with fountek JP3.0 and Peerless XXLS 12" (830952). The crossover will be somewhere between 100-150Hz, so hopefully it will work for me.

/Goran
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Old 13th December 2009, 06:55 PM   #8
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Quote:
Originally posted by SBob
Still, I find it odd that they are so much off.
The older Vifas seem to have some issues with consistency. I have 4 units of 10" Premium Line PL26WR09-08. Measured them with my LMS. All their T/S are different. Looking at the specs alone, you would think they are different drivers.

This is not exclusive to the PL26WR. My other Vifas, a pair of P21WN and M21WO are also not matched. All are new, bought direct from Vifa 10 years back. Looks like Tymphany has sorted out this problem.

Quote:
I am thinking of getting another woofer for my centre speaker, I would like it to go down to at least 80 Hz since that is the cut-off frequency my amplifier uses. The reason I choose the P13 is that I have P17s in the front speakers. Any suggestions on a similar woofer that I can use? Or is 100 Hz OK for a centre speaker even though the amp cuts off at 80Hz?
There's no harm at 100Hz. You don't need to match your amp's 80Hz with the speaker. Personally, I prefer at 100Hz for center.
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Old 13th December 2009, 08:10 PM   #9
SBob is offline SBob  Sweden
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Thanks for your help!

I have now put together a prototype cabinet to see what it sounds like. Will keep me busy the next couple of days.

I guess the upside is that the cabinet is a lot smaller than i had planned for.
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Old 4th February 2010, 09:34 PM   #10
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Default Fs ~ 80Hz

Hi,

I recently purchased a pair of P13s. After a couple of weeks use my free space impedance measurement indicates resonance slighty above 80Hz.

Chas
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