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

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Re: How effective are these foam pads at sound absorption?

Posted by Jon Risch (B) on February 25, 2003 at 21:06:04

In Reply to: How effective are these foam pads at sound absorption? posted by sheppard on February 25, 2003 at 11:32:30:

These types of bedding foams do not have the proper density, nor the proper foam structure to absorb sound linearly.

They often absorb the audio frequencies irregulary, and can even reflect the very HF's to a large extent.

Yes, the thicker foam at a total depth of 4", will work a LITTLE better than the 2" beddingfoam commonly available at WalMart, etc., but only a little better.

True acoustic grade foam is not cheap, and must be used in sufficinet thickness to get good results.

See:
http://www.geocities.com/jonrisch/a1.htm
for details on room treatment (toward the end of the DIY note).

You need a controlled amount of a thick enough material to do the most good. One of the most common mistakes that are made when attempting to treat the room, is to use too thin of a material, and to use too much of it to try and make up for it being too thin.

Fiberglass can be had inexpensively, and enough thickness used to adequately absorb the LFs, and the issue of the glass fibers dealt with, as per my DIY note.

You can also use JUST the polyester batting, the hi-loft kind, as long as it is as thick as necessary to equal the fiberglass. The hi-loft type of polyester equals the natural density of most building fiberglass, and can be layered to the same thickness to acheive the same results.

Now, if you MUST get these types of bedding foams, there ae some tricks that will help make them more linear and less problematic.
First, place a layer of the hi-loft polyester batting over the front surface, wrapped slightly around the edges.
Second, place the foam in a light wooden frame with legs, you can use chiken wire to restrain it, and then place the poly layer over it.
Finally, use the frame to space it off from the eall at elast several inches, this vastly improves the LF absorption over a flush wall mounting.

Cover with burlap or speaker grille cloth for better looks.
Use of other fabrics, no matter how open the weave may seem, is likely to cause uncontrolled HF reflections, and poor midrange absorption as well.

All my DIY acoustics notes are at:
http://www.geocities.com/jonrisch/a.htm

Jon Risch

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