Suggestions on stiffening woofer cabinet?

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I'm retrofitting an existing homebuilt woofer cabinet with 2 8" woofers
and am using this as an opportunity to improve the cabinet.

2 cross-braces and sound deadening foam have already been installed
in the interior, but the 0.75" particle board still resonates when I
rap on it with my hand. The external dimensions of the cabinet are
37"H x 17"deep x 10"wide. Its those 37"x17" side panels that are
killing it.

My current thought is to build outer walls for the sides of the enclosure
and fill the cavity between the inner and outer wall with concrete or
sand. Is this the way to go, or would another layer of 0.75" particle
board glued and screwed to the existing side walls do the trick?

What would be the best way to make these enclosures solid without
reducing interior volume any more?

Thanks in advance,
Keith.
 
Personally I wouldn't spend the time/money to do concrete or sand around the enclosure although it would certainly deaden it. Unless it's really high end stuff it's probably not really worth it. And if the enclosure was originally made of particle board it probably isn't really high end to begin with (this isn't a knock on your sub, mine is particle board too!!). One thing to keep in mind with cabinet resonances is that as long as the resonance is a resonably high frequency the sub won't excite it anyways. So when you rap on it if it's a high frequency (at least higher than whe your sub would play) you probably don't have to worry about the sub itself exciting any cabinet resonances.
 
Go for the sand if you're willing to do it. I wouldnt go too crazy in terms of time/money for cement if you're only using two 8 inch drivers. Try and make the contact points between the inner and outer boxes minimal, so that you decouple the two as much as possible. You also might want to try something on the inside other than foam, such as car dampening sheets. Use these behind the foam; they do a good job.
 
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Keith TDI said:
existing homebuilt woofer cabinet with 2 8" woofer
2 cross-braces and sound deadening foam have already been installed
in the interior, but the 0.75" particle board still resonates when I
rap on it with my hand. The external dimensions of the cabinet are
37"H x 17"deep x 10"wide. Its those 37"x17" side panels that are
killing it.

How have you got the braces oriented? i'd run at least one per side panel 37+" x 3/4" x 1 1/2-2" wide pieces running from bottom to top dividing the big side panels into two unequal trapezoidal panels. Two per side would be better. And at least one on each of the other panels with special attention pad to the baffle.

Each time you divide a panel in two with a stiffener you increase the frequency of the primary panel resonance by 2. If you get all the resonances hi enuff that they never get excited, then they don't matter so much.

dave
 
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