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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Size or Thickness More Important? posted by scvbrent@yahoo.com on February 5, 2007 at 20:28:58:
The biggest single mistake many people make in treating a room, is to use too thin a material, and try to make up for it by using more than the optimal amount of area.So in that sense, thickness is more inmportant.
BUT, there is easily such a thing as NOT being large enough, not having enough area, to absorb lower frequencies.It helps to realize that bass waves are LONG, and that in order to absorb them, to keep them from reflecting off of a wall (such as when you place a wall panel at a first relfection point on a side wall), that the absorber has to have enough physical size to absorb the wave, or the wave will diffract around it, as if it weren't even there.
As an extreme example, some folks recomend placing a 12" by 2 foot piece of plywood on the side wall angled so as to reflect the side sounds away from your ears. Imagine a top down room diagram, with the this plywood panel placed at the first reflection point, and horizontally 'aimed' so that the panel is pointing at you, this will cause the HF's that hit the 1st reflection point to be directed away from you. However, due to it's small size, this panel will only be able to 'direct' or 'aim' sounds above approx. 500-600 Hz, everything below that frequency will tend to diffract right around the panel, so that at lower frequencies, it will be as if the panel is not even there, it is too small to direct those longer wavelengths.
By the same token, a wall panel can be too small to help absorb a lower frequency, even though it has enough depth and wall spacing to do some good at a particular frequency. Note that these things are not absolute, there is no "falling off a cliff" kind of effect, it is gradual, and related to frequency and the physical size of the waves involved.
I do try to stress that the typical pre-fab panels that are 2 feet by 4 feet are only good down to a certain frequency, no matter how thick they are. This limiting frequency is approx. 260-280 Hz, below that they are starting to be to small to effectively absorb enough of a low frequency sound wave enough to prevent it from continuing on as a reflection. This coupled with the all too common practice of only using a 2" or at best, a 4" thick panel, means that most of these panels are only working FULLY down to about 800 Hz, and partially down to about 260 Hz. Below that, they will do very little real good.
That is why the use of true bass traps in the corners should go hand in hand with the use of wall panels, so as to extend the acoustic control of the room down to the lower frequencies.
Jon Risch
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Follow Ups
- Re: Size or Thickness More Important? - Jon Risch 02/11/0720:18:45 02/11/07 (0)
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