What noise damping material is worth the cost?

[tomservo]

What noise damping material is worth the cost?

dynamat, elemental designs, carpet padding, dried monkey poo, whatever you've found effective..

also, was it the low frequency or high frequency type? (asphalt type or foam type)

[bobkoure]

The absolute best I've found is "black hole" acoustic foam.
It's several layers bonded together
- adhesive (peel and stick)
- dynamat-type bottom layer
- thin lightweight foam that simply decouples the limp wall
- "limp wall" layer of vinyl (or some soft plastic membrane that seems to be vinyl)
- thicker absorption layer

There's only three problems with it
- it's thick (so you need to put it into a large case
- it's kind'a expensive
- the company seems to be out of business (or at least not selling to the retail market anymore - this stuff is normally used to damp standing waves in speaker cabinets - and they may still be selling to speaker mfgrs...)

I'd suggest you do a web search for "limp wall" and acoustic. If you're really interested, try F. Alton Everest's Master Handbook of Acoustics

Bob

[Maestro]

Personally I've tried Sonex Wiltec foam and some generic pax.mate akasa type stuff; the Akasa was useless, and the willtec is OK for high/mid frequency whine, but too light to do much else. It's reasonably cheap though, so for the price I'd say it's pretty good. I've also helped a friend put the acoustipack deluxe stuff in his case (and will soon be putting it in mine, after hearing the before and after on his!), and that stuff seems to be the best, but it's NOT cheap. The acoustipack stuff is very heavy and really deadens vibration and whine. It's something like 60 bucks for the standard pack and 80 for the deluxe set. So I guess it depends on what you consider Worth The Cost. The Acoustipack definitely works, but is expensive, while a lot of other stuff is cheap but doesn't do squat.

SPCR's got a review on the subject, mainly the Acoustipack, as they dismiss the other contenders as worthless:
http://www.silentpcreview.com/article71-page1.html

[bobkoure]

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...

[HammerSandwich]

I've only used DIY stuff from McMaster. They have a number of interesting products at reasonable prices, so you probably can afford to play a bit. See the bottom of page 3300 for materials like Bob Koure has described.

[Blackeagle]

I'll add a second vote for the McMasters products.

Not the very best perhaps, but good bang for the buck.

[ricecrispi]

Best bang for the buck is free.

Acoustipak is plain foam, egg foam, and stuff they used for mobo cushioning or lcd covers. Paying for that stuff is silly. You can scrounge for that stuff.

or

Just ask your company's computer vendor or IT guys to get some neoprene mouse pads for cheap. My old employer used to give them out for free for meetings and trade shows because they cost less than $1. I got like 15 out the box. Since they are out of style they might give them all away for free. Some pads are denser than others So i would also just using thin layer of soft foam