I have an argument that I would like to have settled; In another forum, the original poster asked a general question as to why there was what appeared to be cotton stuffing inside his subwoofer enclosure. Here are some excerpts that were posted in response by the person I'm in disagreeance with (Let’s call her Jane):
“It is MOST often referenced to as Poly-fill. It is NOT cotton. Cotton would provide the exact OPPOSITE of what (and why) you are wanting to "fill" your box.”
“As a Mater of fact the ONLY thing adding a loose fibrous material does is convert the "pressure" to heat.”
“As far as the quantity to use... 1 to 1.5 lbs of polyfill per cubic foot volume of the enclosure. It is NOT an exact art, but the benefit is about 25-30% increase in perceived volume.”
So here we have three statements by Jane that to me appear to be incorrect; First of all Jane says that although cotton filler is also a loose fibrous material it would have properties contrary to this polyester filler, secondly that polyester fill is able to convert air pressure into heat, and thirdly that by reducing the air volume of an enclosure by filling it with that you are in fact increasing the "perceived" volume.
To explain the necessity for a certain amount of cubic volume for a subwoofer enclosure, the surface area of the speaker combined with the throw (which is the distance it is capable of moving in and out) displace a certain amount of air space and this creates a certain amount of pressure that causes the speakers itself to have to do more work in order to function. So the smaller the enclosure, the greater the pressure, and the more work that the driver has to do in order to function. I believe most 12” subwoofer manufactures suggest about 1’-1.5’ cubic volume. Jane believes you should use polyester fill in situations where the cubic volume is less that this suggested amount and that it will make up for it. Jane says it doesn't matter where you place the polyester fill, and that in any box where the cubic volume is less that the recommended cubic volume that filling the enclosure with polyester fill makes up for the volume.
Here are two hypothetical enclosures box A and box B:
Box A is a perfect cube measuring 12"x12"x12" inside, while box B is quite similar with the only difference being that the depth is 9" reducing the volume by 25%. Now place 1lb of polyester fill in box B. Jane believes that by placing 1lbs of polyester fill in box B increases the volume to match box A. In box A I would assume the waves constructively interfere, but that’s not really relevant to the air pressure caused by displacement which is what we’re discussing. In box B I would assume that the 1lb of polyester fill would act as dampener. These are sealed boxes, and let's make the subs 10" with a 1" throw, installed in the center of the face of box A and box B.
I’ll briefly explain my perspective. It would appear that this polyester fill is actually just a dampening material. Jane says that it is not and that it only converts air pressure into heat. I’m not denying that in dampening that there is some heat generated, although I’m quite sure that if I were to attempt to measure it that it would be undetectable.
I hope this is the right forum, and that I have included enough information for this to be settled. I would like to thank everyone ahead of time for helping me out.