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Can speaker cabinet vibrations be fixed?

Hi,

Recently I noticed that bass notes cause the cabinet/housing of one of my loudspeakers to vibrate, thus, distorting the sound of the notes. The vibration is at its worst when the speaker reproduces 50-80 hz test tones.

The cabinets for my speakers appear to be constructed of laminated particle board, the pieces of which were assembled using some sort of wood glue or possibly epoxy. The speakers measure 16"W x 28"H x 10"D.
Though the vibrations seem to be originating from the back piece of the speaker, I find that if I place my palms on the left and right hand sides of the speaker and then apply a little bit of pressure inward, the vibrations cease, and then the speaker operates normally once again.

These are not audiophile quality speakers, but if I can make a repair (I refoamed the woofers a couple of years ago), I'd really like to hang on to them.

If it's possible to fix this problem, any advice on how to do so would be very much appreciated. Thank you.
jsangelo
10 responses Add your response
stanwal's avatar
stanwal
3,147 posts
 
Add internal bracing, I had that done to a JBL 150A in the past. If you don't care about looks you could do it on the outside. And/or you might want to try some damping material on the inside of the speaker. Madisound has a book on building speakers that usually costs$35 on sale for $11. If you are going to do speaker repair it would be a good thing to have.
usblues
1,217 posts
 
Concur with Stanwal.Use 2x2 material cut to size,make sure pieces are straight.Should be able to get a screw-gun inside to do the job.Determine screw length on a practice piece as all screwguns have a different torque.Don't glue until your happy,just drywall screws,then go back in after a week or so.Could be the beginning of a new hobby or dare I say it?A new line of employment.Nothing beats wood-working for satisfaction with the possible exception of teaching guitar,YMMV,Bob
bradearles
30 posts
 
I agree with both of the above but think you should combine the two. Use a brace then glue it into place once you like it, let the glue dry, then use a damping material such as dynamat and you should be good to go.
mapman's avatar
mapman
21,838 posts
 
Another very easy and low risk thing to try is to add acoustic absorbing material inside to help dampen things further if that is not already the case.

No physical alterations are required with this. All that is needed is to gain access to the inside by removing the bass driver and carefully add the material in a manner that distributes it evenly to a uniform density throughout the inside. Just be sure to look before you stuff so as not to damage any fragile internal components like crossovers, etc.
Ag insider logo xs@2x
jgiacalo
446 posts
 
Another cheap tweak to significantly reduce cabinet resonance is to apply DynaMat, or one of it's clones, to the inside to the cabinet. Dynamat, and similar products, are sold at auto parts stores for damping metal panels in cars to which speakers are attached. It is a simple, constrained-layer damping material that consists of a sticky, asphalt-like layer mated to a layer of aluminum. It is Very effective at damping vibrations and very simple to apply; simply peel-and-stick to the inside cabinet walls. Costs about $20. for two 8"x10" sheets. Fast, simple, effective, and relatively cheap. Then, if you're really ambitious you can internal bracing. But, you might need it by then
sounds_real_audio
946 posts
 
You should make sure that the screws that hold your woofers in place have not come lose.
stiltskin
499 posts
 
Agree with Sounds real, periodically check all your fastening screws.
Screws will back out over time from vibrations in particle board including shifts in climate especially with medium and high density fibre boards when directly fastened into.

Many speaker cabinets of today are constructed with inexpensive mdf and hdf which are poor materials to directly fasten a screw into, ask any competent cabinet maker.

However checking for loose screws should be part of your system maintenance which ever fastening method used and material your speaker cabinets are made of.

From your description you will most likely find this is the problem. You may get away with simply tightening the screws.
Or
There are many great adhesives available, buy one that is suitable for the screw and particle board.

For the drivers themselves use a drop of motor cycle nut and bolt adhesive, Lock Tight brand or similar.

jsangelo OP
9 posts
 
Stiltskin: unfortunately, no screws were used in the construction of these speakers, but I wish there were, as merely tightening them would've been easy and the first thing I would've checked.

I'll probably need to add some adhesive and/or go with some braces as Usblues and Bradearles suggested. Trying to find suitable screws for cheap, laminated particle board could be a problem, though.

Thank you, everybody, for excellent suggestions all around. ;-)
magfan
1,583 posts
 
Never took one apart.....Don't builders use threaded inserts to secure drivers? I would! And some kind of hard, closed cell foam as gasketing.
sounds_real_audio
946 posts
 
Jsangelo

I was referring to the screws used to install the drivers. When you had them refoam the woofers they unscrewed them. I am guessing that those screws need to be tightened up again. Not a big deal. Give me a call if you need more info.

Jim
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