Is Acrylic an open cell or closed cell polymer? Re: Sound Transmission

We’re building a fairly high end recording studio in my guitarist’s new house, and we’re looking at cast or extruded acrylic sheeting (1/4 or 1/2’’) as a good, relatively economical window material between the control room and the live and drum rooms.

Does anybody know whether acrylic is an open or closed cell polymer?

Also, would anyone know it’s STC rating?

Thanks in advance!


Does it get markedly heavier when you stick it in a tubful of water, then squeeze and release?
Acrylic is usually closed cell, but if it doesn’t say on the box, I’d do a tub test.

I’m confused. You say you want an acrylic window? Open or closed cell refers to foams, which would make terrible windows. If you’re asking about two separate things and want to know about acrylic foams, well, as mentioned, acrylic foams are usually closed cell and they’re stiff, like styrofoam and don’t absorb water. Open cell foams are squishy, like sponges and can absorb water.

No, this is going to be either extruded or cast acrylic, in a 4x8 sheet. I was under the impression that extruded or cast acrylic could come in either cell type.

But I’m a sound engineer, not a materials engineer - I’m pretty ignorant in that regard.

Window?, yeah, what you said.
Sheet acrylic is dense, and thus a pretty good sound deadener. If you want more sound deadening, put in a double pane of 1/4", with about half an inch between the panes. The airspace will minimize direct vibration transfer between rooms.

I’m no sound engineer, but this is what I would do if it were my project.

Yeah, that’s what we were thinking - 2 1/4’’ panels, with a very slight offset angle (just a few degrees) between them so they are not directly parallel vertically - this will also interfere with the sound wave transmission.

thanks again for the replies!

Just a hunch, but I think you might get better sound deadening if you used two sheets of different density. Maybe acrylic (PlexiGlas) and polycarbonate (Lexan) are different. Glass would be much denser, and we’re talking 1/2" or 1/2" sheets here. If you are willing to go three sheets, with a glass one in the middle, you could also use the least safe kinds of glass, because it’s protected anyway.

Why not glass only? Density is a good thing here. Besides, glass doesn’t develop a haze of fine scratches from cleaning it. I also think it’s environmentally friendlier, as it’s basically melted sand, but I don’t have authoritative sources for that.

I found a good article detailing the principles behind soundproofing windows. It’s essentially as Napier outlines: you want at least two of the thickest, heaviest, most dense panes you can find, as large an air gap as possible between them (the benefit of angling is debatable here, it seems; the authors ultimately recommend parallel panes) and have the panes be differing thicknesses. The reason for the latter is that every pane will have a fairly narrow range of frequencies which pass through it quite well; if the panes are of significantly different thickness, the passthrough frequencies of one will be blocked by the other, and vice versa. The idea of angling one pane relative to the other is to reduce standing waves, however, some standing waves will still occur and the angling necessarily reduces the air gap size, which is important to improve low-frequency isolation.