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

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Re: Acoustic absorber panel question

Posted by Jon Risch (B) on April 1, 2006 at 10:41:06

In Reply to: Acoustic absorber panel question posted by greg7 on March 31, 2006 at 21:05:53:

In terms of DIY wall panels vs. retail wall panels, unless you really go out of your way to mess them up, the DIY will perform about as well as the retail devices. The amount and thickness of fiberglass is the main variable, and if you duplicate the density and thickness of a retail panel, then it will perform as well.

Now with that said, some of the retail panels use some "high technology" in terms of absorbing materials, and construction techniques, and some of these are hard to duplicate exactly with DIY designs, but on the whole, a DIY wall panel is going to be VERY close in overall performance for a given thicknes, etc.

Most of the hi-tech absorbing materials make ue of variable density or limp masses or not-so-limp masses to aid in the absorption of LF's.

For instance, comparing a wall panel with JUST building grade fiberglass at approx. a thickness of say 4" at the edge, and about 6" in the middle (6 or 6 1/2" fiberglass inside a 1X4 wooden frame, with no wood panel backing, etc) to a 4" to 6" retail panel, the retail might use a limp membrane on the rear, and a higher density of material toward the back.

This would allow it to absorb slightly more LF energy, and would help keep the room from getting too boomy. However, it helps to realize that the difference is going to be slight, and that making a slightly bigger DIY panel, or using a few more in the room will more than compensate for that.

One can duplicate some of this for DIY panels, by adding in a limp mass to the back, using higher density material toward the rear of the panel, but this adds to the cost and effort to build the DIY panel.
In my DIY wall panwel designs, I have addressed some of these issues, by incorporating (optionally) a rear layer of higher density semi-rigid rock wool or OC 705/706, and using fiberglass with a kraft facing, and leaving the back of the frame open.

Some folks like to use pegboard or a thin plywood panel on the back of the wall panel, and this can usually increase the low bass absorption, but at the expense of the upper midbass and lower midrange absorption effectiveness.

Those who have read my DIY acoustic treatment note, will remember that I found that you could substitute a greater thickness of just the building grade fiberglass and leave off the rear semi-rigid panel. The trade-off is overall thickness is increased.

One other aspect is that most of the retail panels use a Guilford grade cloth covering, while I recomemnd using colored (dyed) burlap or speaker grille cloth as a covering. There is a huge cost differential, but for those who need the extra WAF, the Guilford grade cloth is the way to go.

BTW, you did not ask, but many others do, and I wanted to mention it here as well. The DIY bass traps, as per the original design (not the Super Quick & Dirty design) are pretty much equal in overall performance to the ASC products for a given size, and since you can build them to your specifications, and can build ones that are slightly larger than the retail ASC products, and actually exceed the ASC performance for low bass damping. However, all of this is dependant on following the recipe exactly, and insuring a proper seal around the edges so they do not have leaks at the edges or at the seams.

Same goes for the DIY wall panels, throwing up a 2 foot by 4 foot by 2" thick OC 705 semi-rigid panel against the wall DOES NOT equal the performance of most retail wall panels, since it is not as thick, and does not have a lower density outer layer to help absorb the HF's better. Others have added a solid sheet of 1/2" ply wood or dry wall or paneling to my DIY wall panels, and this will adversely affect the upper midbass and lower midrange performance. As noted in another post in this thread, iof attention to detail is not carried through, then you may not get equaivalent performance.

Jon Risch

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