Constrained layer damping materials?

[TurboFC3S]

For a front baffle, how do you think this MLV (Mass Loaded Vinyl) would work laminted in-between two sheets of 3/4" MDF for constrained layer damping?

http://www.soundproofing.org/infopages/flooring.htm

Obviously I'd be using the one without foam backing

Is there something better that's also inexpensive I should consider? That same place also sells 1/64" and 1/32" lead sheeting at a decent price.

[ThomasW]

Lead? Toxic speakers? Just say no....

If you use our search function you'll find quite a bit of discussion about CLD.

http://www.htguide.com/forum/search.php4?searchid=527783

[KJP]

Would probably work pretty good. The main idea of a constrained layer is to decouple surfaces. You build a box, glue this stuff all around it and then build a box over that. But then you need to mount you drivers to something. Mounting them to that outer box will transmit their vibrations into that shell and out into the air somewhat defeating the constrained layer. Best to mount them to the inner box, maybe becoming a little tricky to finish. So just doing the baffle would make for a pretty high transmission loss baffle but I don't know how effective it would be overall in the long run.

[jdybnis]

The main idea of a constrained layer is to decouple surfaces.

OK, there is some confusion of terminology here. Decoupling an outer and inner enclosure is a great technique and it is well worth trying but technically that isn't "constrained layer damping". CLD refers to a damping layer bonded between two stiff layers. The damping layer will convert the energy from the vibrations into to heat.

For some reason sandwiching the damping layer between two surfaces works much better than just affixing it to a single layer. I don't know the physics of it. A perfect example of CLD is laminating two sheets of plywood together with contact cement. The contact cement is the damping layer. However if you just paint contact cement onto a plywood surface it isn't going to do much.

[KJP]

Decouple may have been a poor word choice on my part. The construction description is still valid to create a CLD enclosure no?

[jdybnis]

Google for "constrained layer damping" the first two pdf's should answer you question.

[KJP]

I had already read them. They are talking about panels and don't seem address creating a box.

[truckman]

I'm curious about how well bonding a metal plate to the inside of the panel with Green Glue would work. For best results I think the glue layer should be on the neutral axis of the structure, which I believe means that the ratio of the thickness of the two outer layers should be proportional to the square root of the ratio of their MOE's. For a 3/4" MDF panel a ~3/16" aluminum plate or a ~0.10" steel plate would be appropriate if my calculations are correct.

From the standpoint of weight added, it looks like using aluminum is basically about the same as using another 3/4" layer of MDF, and steel is a definite loser.

[TurboFC3S]

That Green Glue looks interesting, I'm going to order some of it and the mass loaded vinyl to give it a shot on my baffle. Of course, I guess I'll never really KNOW if it works or not ... since I don't have the resources, time, or even knowledge to properly test.

My hope is that it'll diminsh energy transmitted into the enclosure by mechanical vibrations, and possibly even energy transmitted back into the front baffle by resonances. That could help tweeter performance, and possibly slightly midrange performance.

What about using that Green Glue to attach your Whisper Mat, Carpet backer, open cell foam, whatever to the inside panels of your enclosure?

Is there any way to order back issues of Voice Coil? I've heard they did some tests in the past of many different aspects of encolsure construction and damping materials. Maybe we need to fund our own test study here, I'd pitch in $50

[jdybnis]

I had already read them. They are talking about panels and don't seem address creating a box.

AFAIK most significant resonances in a box are panel resonances.

[KJP]

Very true. My thinking is probably trying to take it farther than needed. I tend to do that..... :roll:

[Martyn]

I just took a quick look at the Green Glue site - it seems to be a sealant that's used to fill gaps and to provide a degree of mechanical isolation. I don't think it will work as an adhesive in constrained layer construction. In this kind of application you need an adhesive with high shear strength, otherwise your MLV or steel sheet isn't going to carry any load - the glue will shear instead.

[ColoradoTom]

Cork

I recently had to buy some cork for one of my girls school projects. It came in a roll up sheet 2' x 4'. Would there be any benefit to using this as a layer for side/rear panels? It would be easy to do for a panel that was going to be supported and wouldn't have the possibility to see any shear stresses.

ColoradoTom

[Dennis H]

In this kind of application you need an adhesive with high shear strength, otherwise your MLV or steel sheet isn't going to carry any load - the glue will shear instead.

And that's a good thing. The actual forces involved are tiny so there is no risk of the glue failing in a shear mode. What you want is a material with that will stretch/flex/shear and have a slow 'recovery' so it will convert the movement energy into heat. From the graphs on the Green Glue site, it appears to be a very good material for that. Sorbathane is also very good but it's way expensive. Bitumen is very good and sort of the standard but it's messy to work with.

[Martyn]

And that's a good thing. The actual forces involved are tiny so there is no risk of the glue failing in a shear mode. What you want is a material with that will stretch/flex/shear and have a slow 'recovery' so it will convert the movement energy into heat. From the graphs on the Green Glue site, it appears to be a very good material for that. Sorbathane is also very good but it's way expensive. Bitumen is very good and sort of the standard but it's messy to work with.

Depends whether you're using the Green Glue (or whatever) as the viscoelastic layer or as an adhesive to stick the viscoelastic layer to the rigid panels. If you're using it as an adhesive, it needs a high shear strength. If you're using it as the VE layer, it will need the mechanical properties appropropriate to that purpose.

[Dennis H]

Given the mechanical properties of Green Glue, I'm pretty sure most people would choose to use it as the viscoelastic layer.

[Martyn]

I recently had to buy some cork for one of my girls school projects. It came in a roll up sheet 2' x 4'. Would there be any benefit to using this as a layer for side/rear panels? It would be easy to do for a panel that was going to be supported and wouldn't have the possibility to see any shear stresses.

ColoradoTom

I recently laminated a picece of 1/4" cork between two pieces of 1/2" MDF. I'd say that it seems to help damp the panel, but I haven't done any serious tests yet. I think that probably any signficant change in density from one layer to the next in laminated construction will help. A layer of cork on the interior surfaces might help to deaden the enclosure at mid and tweeter frequencies, but I can't really claim to be very knowledgeable on this.

[TurboFC3S]

I just took a quick look at the Green Glue site - it seems to be a sealant that's used to fill gaps and to provide a degree of mechanical isolation. I don't think it will work as an adhesive in constrained layer construction. In this kind of application you need an adhesive with high shear strength, otherwise your MLV or steel sheet isn't going to carry any load - the glue will shear instead.

I thought you wanted the 'soft' layer to shear, turning that energy into heat?

I assume I'll have to use a couple screws to hold the baffle, who knows how strong this Green Glue is. But I'm planning on just 4 or 6 screws, enough to keep the new baffle from falling off ... and little enough to hopefully let the Green Glue do it's energy conversion job

[Brian Walter]

I thought you wanted the 'soft' layer to shear, turning that energy into heat?

I assume I'll have to use a couple screws to hold the baffle, who knows how strong this Green Glue is. But I'm planning on just 4 or 6 screws, enough to keep the new baffle from falling off ... and little enough to hopefully let the Green Glue do it's energy conversion job

I seem to recall reading somewhere that even 1 screw through the panel will greatly defeat the effect your are after. If you must use any screws, I'd put them near the center of the panel it will have the least effect on the horizontal shearing action that way.

Brian Walter

[TurboFC3S]

I seem to recall reading somewhere that even 1 screw through the panel will greatly defeat the effect your are after. If you must use any screws, I'd put them near the center of the panel it will have the least effect on the horizontal shearing action that way.

Brian Walter

That would make sense if it were the case. I guess the best thing to do would be a trial run ... glue a couple pieces of MDF together and see just how strong it is.