Speaker rattles cabinetry

[steve77]

Orontes II was delivered 30 years ago with two built-in speakers in the salon. These are on either side of a bookshelf, and are in completely closed enclosures.

I had been noticing rattling sounds coming from our speakers while watching movies and listening to certain songs. I thought the speaker cones were shot.

When I removed the speakers I could not find anything wrong with them. I played some music with the speaker out of the enclosure and it sounded fine. As I reinstalled it (while still playing music), I found the problem. The sealed compartment greatly boosts the bass response of the speaker, and the rattling is coming from a plywood panel above the books.

I can't do anything with the plywood, and was thinking of alternatives. I was considering adding some foam rubber to the inside of the enclosure to provide something to absorb the acoustical energy. If that didn't help I was also considering drilling a 1" or so hole behind the books to allow a path for air to enter and leave the compartment.

Any other thoughts or suggestions? Thanks!

Steve

[paulajayne]

Make up and glue an X brace inside.

[steve77]

Originally Posted by paulajayne

Make up and glue an X brace inside.

Thank you, Paulajayne, but that is not where the rattle is coming from. The rattle is from outside the enclosure, from a plywood panel located adjacent to the speakers and above the books. If you were to lie on your back on the settee and look up above the books, you would be looking at the panel.

There may be a path from inside the enclosure to a space behind (above) this panel, and if so, perhaps air is being driven by the speakers into this space and rattling the plywood.

Any other suggestions?

Steve

[Scott Berg]

I second more bracing (wherever the panel that is rattling is)

[Copacabana]

You could try using some soft rubber washers on the speaker screws (where they hold the speaker). It might absorb some of the vibration.

[djlocker]

• Do you have any access behind the plywood panel? I'd think all you need to do is wedge a rubber plug/shim behind the plywood to dampen the vibration of the plywood itself.
• Alternately, if there's too much space behind the plywood, a larger rubber or foam pad attached to the back of the plywood might also dampen it's movements enough to stop the rattles.
• If there's no access behind the plywood, another alternative would a caulking of some sort along the edges of the plywood where it contacts the other panels in the shelf (assuming the noise is really the plywood rattling against these other pieces).

[steve77]

Thanks, everyone. There is no access behind the plywood panel without removing major joinery. Above the panel, I'm positive there are about two to three inches of sprayed-in foam, followed by the metal deck.

Steve

[jamhass]

You can drill a smallish hole (or 2 or 3) into the plywood panel and spray in a small amount of low-expansion spray foam (type used to seal around window casings). It will expand enough to stiffen the plywood nicely. Try a single hole in the middle first, you can always add more later if needed. Be judicious about it, especially if the space behind the panel communicates with other spaces. And be a bit careful of inadvertently gluing in electrical wires etc and causing problems later.

[hellosailor]

Steve-
That just means you have good speakers, good bass, and lousy cabinetry. With good home speakers and the right music, you can rattle the dishes two rooms away.(G) You don't really show or describe the guilty panel, but if you really only can access the front of it?
The best thing is not to meddle with the speaker enclosure. Putting foam in that won't cut the bass. Cutting holes might hurt the sound.
Can you add another piece on top (below) of the rattling shelf? Say, gluing down a piece of 1x10 lumber, or plywood, or anything dense and rigid to reinforce it and prevent it from vibrating? A real plumbing or roofing store would also have lead sheet (1/16") available, which could be sandwiched in there and that would really eat vibration. Obviously you've have to make it look properly finished, but with firm gluing all around, I'd think it would stop any vibration.

[kentobin]

I have a 1978 Taiwanese plastic boat. The plywood is all delaminated. The wood is good but the glue degraded. This might be your problem. If it is aside from replacing the plywood I've never tried another fix.

When I asked a surveyor I know about the delaminated plywood he said it is quite common on these older Taiwanese boats. His rule of thumb is if the wood has been covered with fiberglass on both sides he leaves it alone, if not replace.

Jamhass had an interesting solution with the small holes in the plywood filled with low expansion foam.

Good luck.

[pesarsten]

Congratulations, it seems that you have found the resonant frequency of you book case. Two easy fixes, get hold of an equalizer and lower the level of the frequency that makes the shelf vibrate, or , try adding some material with a high resonant frequency to the inside of the speaker cabinet. As an experiment, try hot glueing ceramic tiles to the interior of the speaker cabinet in order to decouple it. Think of resonant frequency as the tone generated By a bell, or a piece of steel or ceramic when struck.

[a64pilot]

You have it right, first sound proof, then add a tuned port, idea of a tuned port is that it provides the right amount of resistance to the driver.
If you can get to the inside of the cabinet adding lead sheets may help a swell, you would be changing the resonance frequency by adding weight, should lower it to a point below what the speaker is capable of.

[jamhass]

To clarify:

I meant that the foam goes into the space above the plywood panel, not "into" the plywood. The foam that is already in that space may have delaminated from the plywood (if it ever was) and the new foam is to fill in the space and lightly stress the panes, thus stiffening it.

[SV Siren]

I used to have a friend that had a '68 Camaro growing up, his trunk was the best I have ever heard for bass, it was the shape and volume for just amplifying the lower end. You cabinet might have those same characteristics.

It sounds like you may need some bracing, as well as rubber washers. We nowadays build speaker boxes for fun, and we cut a hole and insert a tube(we use a professional program that determines the sizes) to create a tuned port for the sound to travel. If your cabinetry behind the speaker is sealed too well, it might be creating air pressure that is flexing/vibrating the woodwork, if it is sealed to well, opening up a small hole somewhere might alleviate some of the interior pressure where it wont vibrate, or hum anymore. Adding foam as an acoustic measure might help, you can always put a piece of foam in and let'r rip to see the results.

[Cheechako]

Foam rubber or fibreglass batting should help. stereo enclosures have batting in them. many bass instrument and sound system enclosures do also. Should sound better too. If that doesn’t do it 100% consider cutting a port, maybe 1.5” diameter. I have built quite a few enclosures and experimented with sound systems for 40 years.