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Old 6th December 2009, 04:07 PM   #1
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Default Acoustic Absorbtion for Sub

Hi,

Im building a sealed passive radiator subwoofer and I need to buy some acoustic material to line the inside (specifically on the back wall).

I have tried rockwool, but im dont want to use it as a material, its too problematic. Can you please recommend an alternative?

These are my current options:

Pyrosorb
Foam 1
Foam 2

I cant find figures to quantify its accoustic properties so I would really appreciate some input.

Thanks!
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Old 6th December 2009, 04:21 PM   #2
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Depending on your XO point is, stuffing will likely have a minimal effect. Lots of dedicated woofers don't use it at all as it's value is lost below certain frequencies. If you still want to use it and don't like rock wool and don't have access to Saltspring Island lambs wool felt then go to your local fabric store and buy some polyester pillow stuffing. It's cheap and will give you the satisfaction of knowing you've added something.
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Old 6th December 2009, 04:32 PM   #3
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If you want to experiment a little without going broke look up "rubber supply" on the web or in the yellow pages. If you live near a reasonably large city one of these places will carry synth and natural rubber solid and foam in varying densities and thinknesses and sell it by the foot. You're likely to find exactly the same stuff that goes by the trade name "acoustic nirvana" (or somesuch) down one of the aisles under the name "poly barrier no#3" (or somesuch) for 1/8 the price.
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Old 6th December 2009, 05:16 PM   #4
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The idea is to reduce standing waves and reduce mechanical sound on the back wall. From what ive read about subwoofers it is best to deaden a sealed sub as much as possible. Is this not true?
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Old 6th December 2009, 07:24 PM   #5
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Quote:
Originally Posted by spadez View Post
The idea is to reduce standing waves and reduce mechanical sound on the back wall. From what ive read about subwoofers it is best to deaden a sealed sub as much as possible. Is this not true?
No, at very low frequencies the wavelengths are too large to get any real absorption with foam or fiberglass etc.

If the subwoofer cabinet was a TL design, then the stuffing is used to attenuate some peaks and troughs in the frequency response.

If the subwoofer cabinet is a front loaded horn design, then the stuffing is there to effectively change the sound velocity (in the rear cavity), which in turn "makes the rear volume seem larger". This could be useful for reactance annulling, for example.
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Old 6th December 2009, 07:53 PM   #6
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Thank you for the help. I think I'm in a little over my head here, if I give you a little more information would you mind giving me a little more info.

Here is my sub build (at the top)
Peerless 830500 830548

Currently it is an mdf shell, no lining, no stuffing. Is there anything I can stuff or line my sub with to improve performance? My crossover is at 90hz. The sub has been designed to hit 20hz.

Thank you for the help
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Old 6th December 2009, 10:12 PM   #7
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I have the same driver/passive combination in a sealed enclosure - no stuffing required really - however the enclosure should be heavily cross braced to reduce panel resonances and consider lining just the side opposite the driver/passive with this type of foam it does help a little in smoothing/reducing any harmonics that get generated from the driver.
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Old 7th December 2009, 04:06 AM   #8
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Quote:
Originally Posted by Cal Weldon View Post
... then go to your local fabric store and buy some polyester pillow stuffing. It's cheap and will give you the satisfaction of knowing you've added something.
+1 Fill for comforters was what I went with. Really cheap, too.
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