The Akasa isn't
totally useless - it's just that it's thin enough that it's really only reducing frequencies that most of us (myself included) can't hear.
Probably makes your dog happier, though.
... And remember that higher frequencies have a way of becoming lower frequencies when re-radiated, so it does do
something... (see excitation/re-radiation below)
Here's a (somewhat-over) simple way to think about absorbing sound:
- sound energy "waves" alternate between pressure and motion (so if you're visualizing it as those sine waves, think of the peaks as being motion and the mid points as being pressure).
- the length of the waves varies with frequency, higher frequencies being shorter.
- when a sound wave bounces off something, that becomes a "pressure" part of the new wave (so motion is a half wavelength away)
- absorbtive materials (foam, cloth, fiberglass, whatever) work by allowing air motion but with
friction - so some air motion is converted to heat. (which also means absorbtive materials essentially do
nothing to the "pressure" part of the wave)
See how there's a direct relationship between the thickness of the absorbtive material and the frequencies it can attenuate?
Yes, there are lots of other issues: how well the material converts molecular air motion to heat, whether the top surface of the material actually reflects sound itself (a factor in choosing an absorbtive layer is finding a balance between letting the sound in, so low surface reflectivity and high molecular friction once the sound
is in).
But that's an easy way to think about sound absorption.
I've used the acoustipack. It works but is (IMHO, of course) vastly overpriced. Instead, look at what speaker builders use do damp standing waves in their cabinets - for instance
sonic barrier foam at Parts Express.
Don't forget that reflection is not the only way that sound gets out of your PC case. The sound waves bouncing against the inner parts of your case can "excite" the panels so they work like speakers, re-radiating the sound. There are at least two ways to reduce this.
- increase the mass of the panels so they don't easily excite - and their "resonant point" is below what we hear as sound. You can use asphalt, lead, dynamat, rubber backed carpet squares, etc, for this.
- keep the sound away from the panels. This is what a "limp wall" is all about. The sound is bouncing off a membrane (which is free to vibrate a bit and so convert some energy to heat right there), that's held away from your panel by very light weight foam.
Anyway, that's why I liked the "Black hole" stuff so much.
- top surface textured for low reflectivity
- thick top layer efficient at absorption
- limp wall membrane
- light weight foam between limp wall and bottom layer
- "dynamat-like" bottom layer
And it was on peel-and-stick to boot, so no screwing about with contact cement (my wife objects to the smell when I'm doing it in the Winter - otherwise I'm doing this in a garage workshop). I suspect it was discuntinued because speaker builders don't usually use a dynamat layer - if they want more mass they build cabinets with thicker MDF
Oh - I'm not any kind of trained audio engineer, BTW...