What's Best for Lining Internal Subwoofer Walls? - Page 2

The reason to keep the covers on the pillows is the keep the polyfill from getting everywhere, especially around the driver. Because of that I normally just arrange them in there but do not staple or glue them which is normally not needed in a home environment were you hardly move the sub around. You want them in there snug but you don't want to compress them much and leave some space behind the subs vent.

good deal, gracias.

James

Sound waves travel slower through the polyfill so it has the net effect of making the box seem bigger rather than taking away from the internal volume. The right amount of polyfill depends on the type of box and the box size. Sealed boxes continue to show gains from increased polyfill density well after the point increased polyfill becomes detrimental in a ported box.

In a small ~1.4ft^3 ported box of mine I found a relatively light amount of poly fill of ~8oz per ft^3 was the right amount. Additional polyfill did not lower the tuning point any more, but instead began to reduce the output of the port and the driver on the knee of the frequency response curve.

In a small ~1.4ft^3 sealed box up to 24oz per ft^3 was still showing gains though they were getting pretty small as I crammed in more and more polyfill.

Keep in mind this was loose polyfill, not a pillow.

Since the speed of sound is constant in air and doesnt speed up or slow down, the lining/stuffing produces gas/particle friction converting some of that energy into heat. The sound wave continues on at same speed but with less "pressure."

The reduction in the speed of sound is cursory at best, and it does not make the box seem bigger. The higher coefficient of resistivity of damping materials, as compared to air, causes a lowering of the system Q, which in some ways emulates a larger box, but it does not duplicate it. Said heat is a by-product of the Q lowering action, not the cause for the lowering of Q. It all boils down to system impedance, which changes with damping, and can be seen on impedance sweeps.