Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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When I bought mine.....

Posted by Winston Smith (A) on December 16, 2014 at 14:50:08

In Reply to: Speaker cabinet foam lining material posted by genungo on December 16, 2014 at 09:42:21:

.... decades ago, the acoustic foam I bought was sold by its density, i.e., its weight per cubic measure (i.e., foot, yard, meter, or whatever), and that was also how you determined it's frequency attenuation in the lower octaves, by its density, e.g., weight/volume. The greater the density, the lower the frequencies attenuated. (At least, that was the theory way back when.... )

I'm sure things have changed a lot for acoustic foams in 20+ years, but I suspect that the basic issue is still weight/volume/density. Thus, if you can get a piece of the stuff and weigh it to figure out its weight/volume, that would likely give you the type of density of material you need to be looking for if you want to match the original designer's choices.

In short, I'd just cut a 1" cube and weigh it out, multiply by 1728 and that should be your approximate weight per cubic foot. Once you've got the weight/volume nailed, you should be in a better position to get what you need to match what was originally installed. However, I would err on the side of more weight per volume being needed than what you measured, as the foam may have dried out and lost weight with time.

As for the exact type of foam employed, I am not sure that is such a big deal (others can chime in if not so) compared to getting the density correct, as the foams I looked at so long ago were all pretty much VERY similar stuff to Sonex, and basically 100% fungible. I went with the Sonex knock-offs, as they were MUCH cheaper and looked/felt basically indistinguishable from the real deal at far less price.

Sonex products currently employ foams that are either urethane or melamine (depending on fire safety requirements, it appears), and claims both are functionally equivalent sonically.

So if you find some cheap acoustical foam of the same density as your old stuff, and it is a urethane or melamine, you are looking at essentially a Sonex clone. Your old foam, being dark, may have been the urethane type, as these are dark brown or charcoal-colored in the Sonex line-up (melamine is usually light/white, but can be dyed darker, BTW.)

Gosh, I hope this helps and does not mislead. Of course, there are REAL speaker mavens out there who are up to date and current on all this stuff, and if they say different, GO WITH WHAT THEY SAY! ;-)

Best of luck, genungo! Let us know how it all works out for you.

Cheers,

WS

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