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Re: Jon Risch bass traps and panels.. My room goes boom boom

Posted by Jon Risch (B) on October 17, 2005 at 19:50:46

In Reply to: Jon Risch bass traps and panels.. My room goes boom boom posted by Aaron 01 on October 16, 2005 at 20:49:55:

Knowing the exact frequencies will not really be that much help, the kinds of devices that need this info are hard to build, and tricky to tune, and should not be attempted by amatuers.

Re the pegboard versus higher density panels, vs. 8" of fiberglass.

1st, the 8" of fiberglass versus the rock wool panels or OC 700 series panels.

When I first designed my sound absorbing wall panels, I was able to get some "high density" rock wool panels for the backs. These helped extend the sound absorption down lower than just the 3 1/2" of fiberglass I had been using, while adding minimal additional thickness to the panels. They also helped keep the frame square when glued to the back.

However, rock wool panels became harder to come by, due to numerous law suits and several rock wool suppliers going out of bussiness (years ago), so I looked into how well just adding sheer depth of fiberglass worked. Panels with a 6 or 6 1/2" thickness were working almost as good as the 3 1/2" fiberglass with the rock wool panels, and when 8" fiberglass was used, the LF absorption was as good or better than the 3 1/2" plus RW panels.

So I now say that use of an 8" thickness of fiberglass works well, and that I recommend a minimum of 6" of fiberglass, not to worry about the RW or OC700 panels. If you can easily get the panels, and they don't cost much, or are free, then by all means go for them.

2nd, the pegboard versus a panel or 8" of fiberglass.

Pegboard panels (the hardboard with the holes in them) absorb some small amount of bass. But they do so selectively, and absorb certain frequencies more, and certain frequencies less. This is a far from ideal situation, and does not help with room acoustics that much, because of the unpredictability and uncertainty. If you don't use enough sound absorbing material in front of them, they can reflect some amount of midrange and/or HFs.

I went to the website you referenced, and it seems that they are using the pegboard more for a backing to be able to compress the fiberglass down about two to one, and to hold the frame together as well. These are also a bit small at 2 by 4 feet, you really need more area to absorb bass well.

Acoustically, you would be better off cutting out the middle of the pegboard, and leaving it mostly open to the rear, and mount the panels away from the wall several inches. In all cases, except where there is a significant amount of solid wood or other very high density (relative to fiberous materials) material, spacing the absorbing material off the wall several inches helps the panel absorb more LF energy.

Owen's extruded polystyrene foam is strictly an insulating material, and NOT an acoustic absorbing material.

RE the bass traps.
There is no substitute for a well done bass trap, and wall panels ARE NOT BASS TRAPS. Yes, you can get a sound absorbing wall panel to get down fairly low, but it wil not absorb as much deep bass as a good sized tubular pressure based bass trap.

Re the Quick & Dirty bass traps, I now recommend doing the Super Quick & Dirty Bass Traps, as described in this post:
http://www.audioasylum.com/audio/tweaks/messages/15737.html
and petew's post where he goes into detail on what he did.
http://www.AudioAsylum.com/audio/general/messages/70817.html

About as simple and as easy as it can get. Make sure to purchase fiberglass rolls where the plastic bag is intact (or can be duct taped sealed), stack up two or three rolls, one stack for each corner, tape the rolls together with tape at the top (and bottom) edges of the rolls, wrap with a layer of polyester batting, cover with burlap (jute) or speaker grille cloth, and stack in each corner.

These are not as economical as the original DIY bass traps, but they are quick and easy to make, and still don't cost that much. They work by sheer brute force, just plain lots of fiberglass in the corners.

Re the Audiogon panels, they look "OK" for sound panels, but one thing for sure: they are NOT bass traps, and even placing them in the corner will not provide that much bass trapping. 60% absorption at 125 Hz is not that much absorption, as it means that they are likely doing very little below that frequency. Note that these are also too small to really have enough area to absorb lower frequencies well. You need some area to do that, not just thickness, hence my recommendation for a minimum panel size of 30" wide by 48" tall.

I have pics of the various panels and traps at my web site, see:
Pic of Wall Panel:
http://www.geocities.com/jonrisch/wp.htm

pics and diagrams.
http://mysite.verizon.net/vze22yzp/id4.html
https://gallery.audioasylum.com/cgi/view.mpl?UserImages=31994&session=

Pics of Bass Trap construction (not finished/covered):
http://www.geocities.com/jonrisch/basstrap.htm

Jon Risch

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

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