"GREAT STUFF" expanding foam as acoustic treament?

[Dirk]

Does anyone have a rough guess as to how "Great Stuff" expanding poly foam works as a sound insulation in a constrained layer? Specifically for midrange frequencies.

[fbov]

Re: "GREAT STUFF" expanding foam as acoustic treament?

As I recall, this foam hardens. You really want something that remains pliable so it can absorb sonic energy and dissipate it to heat by internal friction.
Frank

[depthsounder]

Re: "GREAT STUFF" expanding foam as acoustic treament?

It doesn't harden all that much. When fully cured it is still fairly compressible. I would advise against it because it is a royal pain in the "commonly used corner joint" to clean up and apply uniformly. If you tap on a cured bubble it doesn't sound all that damped anyways. It's kind of expensive to boot.

-David

[PWR RYD]

Re: "GREAT STUFF" expanding foam as acoustic treament?

When you say "in a constrained layer" do mean sandwiched between two layers of wood?

[Dirk]

Re: "GREAT STUFF" expanding foam as acoustic treament?

I'll cop to it. My midrange enclosure in my current build isn't stout enough and I'm getting more leakage out the back than I'd like. I'm somewhat hampered by the boxes being all buttoned up, so I was thinking of things that I could do. On the inside of the midrange enclosure I'll be applying sonic barrier in addition to the poly I've got in there now. On the back side, I was thinking of either applying the foam or liquid-nailing a number of ribs to increase rigidity.

I've got a method in mind to apply the foam with minimal overshoot by placing a "form" behind the midrange enclosure and then drilling a couple holes from the front to blow the foam through. When done, I'd plug/seal the holes solid. The midrange enclosure would then be backed by 1"-3" of the poly foam.

But you guys are right--this would be totally un-reversible. So I'm very hesitant to try it.

[Kevin G.]

Re: "GREAT STUFF" expanding foam as acoustic treament?

Another option and not as aggressive as the "Great Stuff"...we use in the autobody industry every day. Sound deadening, durable, adhesive, expandable... not as out-of-control as Great Stuff..not very cost effective, however...AND you need the gun to deploy the stuff.... 3M automotive and
Pillar Foam
It does start to set up rather quickly, but if you keep it moving, you're good...I have run it through rubber tubing in hard to access areas of a pillar

[PWR RYD]

Re: "GREAT STUFF" expanding foam as acoustic treament?

How about adhering a 1/4" thick piece of plate steel cut to size?

[Dirk]

Re: "GREAT STUFF" expanding foam as acoustic treament?

How about adhering a 1/4" thick piece of plate steel cut to size?

Can't. My solutions are limited to whatever I can fit through the woofer hole. And I have to do it blind. And basically one-handed. That's why my first thought was vertical reinforcing ribs of 1" strips of MDF, with a viscous glue. I could apply the glue to the rib, carefully get it up in there, and press-fit it. However, a coworker mentioned the foam and that sent me down this strange path.

Hindsight being 20/20, I should have just built a damned normal chamber.

[CokewithLime]

Re: "GREAT STUFF" expanding foam as acoustic treament?

That's why my first thought was vertical reinforcing ribs of 1" strips of MDF, with a viscous glue. I could apply the glue to the rib, carefully get it up in there, and press-fit it.

+1 for this idea - use PL Premium (wear disposable gloves) then give it overnight to completely cure - should solve both issues

[patrickm]

Re: "GREAT STUFF" expanding foam as acoustic treament?

urethane glue. (like gorilla glue). you need very little, expands to fill small gaps, and just use some tiny clamps in a push configuration to hold them against the wall, or just put that side down and lay a weight on it. i just did the push-clamp with the tiny irwin squeeze clamps on a sub brace and it worked well.

[Wolf]

Re: "GREAT STUFF" expanding foam as acoustic treament?

Since I've a visual of how you did that... The Sonic Barrier will help damp the resonances, but what do you refer to as 'leakage'? The semicircular wall flexes? If it flexes, then the ribs are your best idea. I would use your wife's vanity/compact mirror to see what is going on. I've done this a few times.

If it's just an air-leak, then you should just use polyurethane glue at the seams, and it'll seal it up. If you don't want expansion, use a Dap project and shmear it everywhere necessary. If you want more options, get a can of Duplicolor Truck Bed liner, and paint it in the gaps after you caulk it. Be advised- it STINKS, and should not be inhaled, but it does the trick sometimes. They make it in a spray-form, but I prefer glopping it where I want it. It will add rigidity to the cardboard. Offgassing has some nasty shtuff in it, so it can dissolve glues if not properly vented and cured.

I know this might be a stretch- but if you can get a smaller piece of the same chamber material in through the hole and thenposition okay, you might be able to Great-Stuff between the layers. I know the cardboard is relatively agile and can be moved in placement.

Later,
Wolf

[Æ]

Re: "GREAT STUFF" expanding foam as acoustic treament?

You can test it out. Do a before and after. Get a piece of MDF, plywood and maybe a piece of sheet metal or metal pipe. Knock on them, knuckle test before the foam and after foaming them. Should be easy enough.

I say probably not. Foam is not dense enough, not very pliant. Carpet padding is better.

[Flint]

Re: "GREAT STUFF" expanding foam as acoustic treament?

What you need for CLD is something rubbery, not something foamy. Well, a foam rubber would probably work. Great Stuff is a stiff closed cell foam, and it's not going to be useful either as acoustic absorber or vibration damper. It is possible to get silicone rubber in liquid form, used for making molds for casting resin or concrete. That would probably work very well for this purpose. It's not cheap though, and may be messy to work with.

[bangleiii]

Re: "GREAT STUFF" expanding foam as acoustic treament?

Plaster mixed with wood glue "no water" poored into the speaker will stiffen the back pannel.

[edlafontaine]

Re: "GREAT STUFF" expanding foam as acoustic treament?

Use silicone caulk as an adhesive...you can also put your gloves on and dab it into the corners to seal leaks...works for both

Consider vinyl composition tiles, 12" X 12" floor tiles, cut to fit, as the "mass" layer