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Old 2nd March 2010, 02:51 AM   #1
xyrium is offline xyrium  United States
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Default How to test for a blown woofer

Hello Folks,

I think I have a blown woofer on a pair of kit speakers that I bought. Is there a way to verify this with a multimeter, or T/S parameters? I hear a fair amount of buzzing when the driver reproduces low freq's. Also, I removed it and applied slight pressure to move the cone in and out, and discovered there was a sound that I can only assume is the voice coil rubbing.

The drivers measures the same as the seemingly undamaged driver from T/S specs, and DC resistance perspectives.

Thanks!
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Old 2nd March 2010, 03:08 AM   #2
audi0 is offline audi0  Australia
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Default Blown woofer

You may have overheated the coil and caused it to distort, therefore making it rub, a continuity/resistance test probably maybe won't tell you a lot.
Worst case would be a re-coil
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Old 2nd March 2010, 10:54 PM   #3
xyrium is offline xyrium  United States
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Thanks. The problem, or benefit depending on how you look at it, is that these drivers have no right playing down to 30 or 20Hz. However, using REW, I measured response to be down only about 6dB at those frequencies. Instead of rolling them off, they actually try to reproduce them. They definitely need to be crossed over at 50Hz or higher for normal listening IMO.
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Old 2nd March 2010, 11:38 PM   #4
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I have always thought that a good driver will reproduce one octave below resonance.

But a subwoofer with a crossover set at 80 can make most speakers sound better.
With the proviso that the XO is active and not just a single cap in the signal path, although that said I have a cheap Ratshack sub that uses that type of XO and I found that with one set of speakers it actually worked quite well, but XO was much higher at 140/180
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Old 2nd March 2010, 11:49 PM   #5
xyrium is offline xyrium  United States
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Gosh, I hope not. Fs on these is 27.5Hz! That's the "bad" news, because they're only 6.5" drivers!
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Old 3rd March 2010, 12:07 AM   #6
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Scan Speak??
how efficient is that woofer?
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Old 3rd March 2010, 12:42 AM   #7
xyrium is offline xyrium  United States
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Not sure if you meant anything other than electrical terms, but here are the specs:

http://www.scan-speak.dk/datasheet/18w_8531g00.htm
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Old 3rd March 2010, 08:26 AM   #8
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You do the 18W8531 a big favour by not letting them do the really low bass. For my use I have an F3 of 55Hz in a sealed enclosure. I have tried them in a vented with an F3 of 35Hz and certainly too low for the driver plus the mid quality suffers.

Just because the driver can do it, doesn't mean it should be done.
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Old 3rd March 2010, 10:06 AM   #9
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Quote:
Originally Posted by xyrium View Post
Gosh, I hope not. Fs on these is 27.5Hz! That's the "bad" news, because they're only 6.5" drivers!
It looks like (from paper) those $200.00 Revelators are all similar with "sub" glitches well under 70Hz, Scan Speak, 15W8530K00 - 8530 by: Scan Speak - Meniscus Audio Group, and they have low SPL. That's the driver in many ("monitor") kits https://www.wilmslow-audio.co.uk/cat...4fd0e5eb59c4d0
Lesson to learn, good marketing is not always good drivers. I always had a reserve from the first day but people seem to like it. If they are bad as a woofer driver it can not be used as a monitor, only as low SPL mids.
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Old 3rd March 2010, 12:20 PM   #10
xyrium is offline xyrium  United States
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THat's exactly what I've asserted to the vendor. I'm trying to get the vendor to replace both of the woofers so I have a fresh pair, since they are only 2 months old. No design should use these full range, you'll kill 'em with just 90dB amplitudes.

I'm in a sealed 30l cab and should be getting a similar F3 as you. However, when I measure their FR, I still get strong output at 30Hz (only 6dB down). So, I stuck an active crossover in there (24dB LR) to high pass them at 40. I suppose it was already too late though.

Quote:
Originally Posted by rabbitz View Post
You do the 18W8531 a big favour by not letting them do the really low bass. For my use I have an F3 of 55Hz in a sealed enclosure. I have tried them in a vented with an F3 of 35Hz and certainly too low for the driver plus the mid quality suffers.

Just because the driver can do it, doesn't mean it should be done.
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