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Two samples of used speakers measure differnetly???
Two samples of used speakers measure differnetly???
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Old 9th May 2008, 02:40 AM   #1
pjpoes is offline pjpoes  United States
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Default Two samples of used speakers measure differnetly???

How different is acceptable. I bought some used Focal TC120TDx tweeters and 6W 4252 drivers, and they measure a lot differently from each other. I can include the graphs of the impedance to show you, as thats all I have measured really at the moment. This is using the Woofer Tester 3 from dayton. Addittionaly, while one tweeter measures .2 mh of inductance, the other measures none??? That doesn't make sense does it? WIth the midbass drivers, one of the cones seems to be of slightly lower mass I think. One of the woofers has an FS of 50.4 hz free air and the vas comes out at like .66 cubic feet. The other driver has an fs of 49hz and a vas of .72 cubic feet. Neither of those numbers are even close to the manufacturers specifications for the driver. The Focal spec sheet has a vas of .9 cubic feet and an FS of like 42hz.

As for the tweeters, those are the drivers that I think are more concerning. The first tweeter file I will attach has specs which are close to the manufacturers specs. The impedance plot looks the same, but the FS is still around 150hz higher than speced. However, the other driver has a completely different looking impedance plot, doesn't even look like it should, and its fs is almost 1000hz higher, at over 2000hz, instead of 1080hz (Spec is 860hz or something like that). Is this make sense, or is there something possibly wrong with these drivers?

I did try using the different impedance plots (zma files) in speaker workshop to see what kind of difference it would make to the response, and it was very minor, but that isn't taking into account differences in the response of the drivers (Which I still need to measure).
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File Type: jpg tc120tdx acomp.jpg (19.3 KB, 349 views)
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Old 9th May 2008, 02:42 AM   #2
pjpoes is offline pjpoes  United States
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Here is the second tweeter, notice the pretty major difference in the plot.
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File Type: jpg tc120tdx bcomp.jpg (37.2 KB, 337 views)
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Old 9th May 2008, 03:27 AM   #3
pjpoes is offline pjpoes  United States
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hmm Ok I decided to recalibrate the WT3 and make sure it was warmed up plenty, then use Nickles and Bluetack for the added mass to remeasure VAS. My scale isn't too good, and measures 3 nickles, a little tape, and a small dab of blutack as 15.4 grams. The cone measures 5.2 inches from the middle of the surround, but only 5 inches or so of actual measurable cone area. I thought I read once that you should measure to the middle of the surround though. Is this right? That measurement has a pretty sizable effect on the vas reading. Anyway, going with 5.2 and 15.4 grams, I get a vas reading of .86 cubic feet for one and .94 cubic feet for the other. The FS reading is, again, different, with 48hz for one and 52hz for the other. Should I be concerned about these differences, or are they pretty minor overall?
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Old 9th May 2008, 04:45 AM   #4
planet10 is offline planet10  Canada
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Two samples of used speakers measure differnetly???
Well made drivers will often be 10%, typical is within 20% and some will be even more.

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Old 9th May 2008, 02:16 PM   #5
pjpoes is offline pjpoes  United States
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After I took those measurements I decided to retest the tweeters to get the T/S parameters and compare again. I again had pretty wildly different numbers. I then retested the woofers, just moments after doing it before, and suddenly the numbers became drastically different. Maybe I should average all my measurements and go with those!!!! In all seriousness, when I remeasured them the woofer with the lower FS dropped to close to spec, around 42hz, and the vas was around .96 cubic feet. Then I measured the other, FS was around 51hz and the vas was around .72 cubic feet. That is over 20 percent different. While Focal is known to be a high quality speaker designer, and the drivers appear to be well made, I actually know nothing about how good they really are.
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Old 9th May 2008, 02:20 PM   #6
SY is offline SY  United States
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Two samples of used speakers measure differnetly???
Q: How did you make all the connections? This sounds like the results I get when I use clip leads and other unreliable methods.
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Old 9th May 2008, 04:04 PM   #7
Inductor is offline Inductor  Portugal
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Also have in mind that T/S parameters will differ after breack-up, they are not the same when new.
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Old 9th May 2008, 04:44 PM   #8
planet10 is offline planet10  Canada
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Two samples of used speakers measure differnetly???
If you can't get reapeatable measures then something in your setup is not right. Do keep in mind that the driver has to be steady & away from surfaces (a clamped stand is best), and that external noise (a hifi playing for instance) can affect things as the speaker is also a microphone.

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Old 9th May 2008, 05:36 PM   #9
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Two samples of used speakers measure differnetly???
Quote:
Originally posted by planet10
I... and that external noise (a hifi playing for instance) can affect things as the speaker is also a microphone.
http://www.diyaudio.com/forums/showt...521&highlight=

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Old 9th May 2008, 10:23 PM   #10
Inductor is offline Inductor  Portugal
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Default Re: Two samples of used speakers measure differnetly???

Quote:
Originally posted by pjpoes
... I bought some used Focal TC120TDx tweeters and 6W 4252 drivers, and they measure a lot differently from each other.
also/or they may not be of the same model/year, or only one was repaired/broked.
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