There are many kinds of acoustical absorbtion materials. Most of the ones I've seen have been based on paper pulp or rockwool.
Do a search, loads of manufacturers will show up.
There are different types for different frequencies, so you gotta measure where your problem is.
Another point to keep in mind is that a room becomes unpleasent to be in, if it's too dead, which is fairly easily achieved. I have recently seen that happen in an other application for a "dead" room.
Magura
Do a search, loads of manufacturers will show up.
There are different types for different frequencies, so you gotta measure where your problem is.
Another point to keep in mind is that a room becomes unpleasent to be in, if it's too dead, which is fairly easily achieved. I have recently seen that happen in an other application for a "dead" room.
Magura
I'm just trying to get an idea of how many feet of said material I'd need to have a 1.0 absorption coefficient at 10hz.
4" of Corning Owens 703 Rigid Fiberglass has a 1.0 absorption coefficient at 200hz (close to 125hz), so if we scale the depth with frequency (200hz to 10hz) we get about 80". I was wondering if there were any materials that were denser (assuming denser provides higher absorption coefficient) or had more efficient absorptive properties/vs length.
4" of Corning Owens 703 Rigid Fiberglass has a 1.0 absorption coefficient at 200hz (close to 125hz), so if we scale the depth with frequency (200hz to 10hz) we get about 80". I was wondering if there were any materials that were denser (assuming denser provides higher absorption coefficient) or had more efficient absorptive properties/vs length.
You don't say what you are going to use it for. If we are talking about absorption in a room, the placement of the absorbent is very important.
The reason for this is that fibreglass/rockwool mainly absorbs when the air is squeezed between the fibres and loses energy. For this to happen the air molecules have to have a velocity, and near a wall the particle velocity is near zero. Now, what is "near a wall" if defined by the actual distance in relation to the wavelength. This in turn makes any absorbent based on "air squeezing" practically useless for low frequencies if placed near a wall. If the same amount of material is placed far away from the walls, the absorption factor increases dramatically at low frequencies.
The bottom line here is that the absorption coefficient and how it varies with frequency is not a material property alone, it is something that is also determined by the geometry and placement of the absorbent.
In real life it is rarely possible to place the material more than a fraction of a metre from the walls/ceiling. The solution to absorb low frequencies near a wall is to make the absorbent pressure sensitive, rather than velocity sensitive. One way to do this is to use tubes, helmholtz resonators or panel resonators.
The reason for this is that fibreglass/rockwool mainly absorbs when the air is squeezed between the fibres and loses energy. For this to happen the air molecules have to have a velocity, and near a wall the particle velocity is near zero. Now, what is "near a wall" if defined by the actual distance in relation to the wavelength. This in turn makes any absorbent based on "air squeezing" practically useless for low frequencies if placed near a wall. If the same amount of material is placed far away from the walls, the absorption factor increases dramatically at low frequencies.
The bottom line here is that the absorption coefficient and how it varies with frequency is not a material property alone, it is something that is also determined by the geometry and placement of the absorbent.
In real life it is rarely possible to place the material more than a fraction of a metre from the walls/ceiling. The solution to absorb low frequencies near a wall is to make the absorbent pressure sensitive, rather than velocity sensitive. One way to do this is to use tubes, helmholtz resonators or panel resonators.
very well said Svante!
thadman, fiberglass and rock-wool has almost the same absorptive data if same compression (so same weight). Any store of products for heat insulation has large range of products...the more density, the more absorption in the bass range.
Follow what said Svante, he is right; if you don't have enough room to place rock-wool panels at least 1m far away from walls you will not get any low-bass absorption.
thadman, fiberglass and rock-wool has almost the same absorptive data if same compression (so same weight). Any store of products for heat insulation has large range of products...the more density, the more absorption in the bass range.
Follow what said Svante, he is right; if you don't have enough room to place rock-wool panels at least 1m far away from walls you will not get any low-bass absorption.
Density of a material (or the 'interstices') does have an effect on the absorption coefficient but going denser will not always give better absorption at lower frequencies. 3lb/ cu ft gives about the best performance. If you go higher like 6lb/ cu ft then the low frequency absorption only improves a very small amount and high frequency suffers as the 'weaker' waves can not penetrate in to the material.
As Svante has said the placement is important. If you place an absorptive material at a set distance from a boundary and run a signal sweep you will see comb filtering because maximum absorption is achieved at a point 1/4 wavelength from the boundary of the frequency you wish to absorb. So to absorb 100Hz effectively you want the material centered on a point 85cm from the boundary. Odd multiples of the 1/4 wavelength also absorb well. Anything else is poor.
Obviously, thickness has its affect too.
As Svante has said the placement is important. If you place an absorptive material at a set distance from a boundary and run a signal sweep you will see comb filtering because maximum absorption is achieved at a point 1/4 wavelength from the boundary of the frequency you wish to absorb. So to absorb 100Hz effectively you want the material centered on a point 85cm from the boundary. Odd multiples of the 1/4 wavelength also absorb well. Anything else is poor.
Obviously, thickness has its affect too.
hi again, is this the same stuff? http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290141544186
can i use this for my enclosure stuffing?
thanks
can i use this for my enclosure stuffing?
thanks
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