Originally posted by Sleeper:
The polyester fiberfill (aka polyfill) is a good idea in more ways than one.
First, it slows down the sound waves from the speakers, causing the rattle to dissipate some.
Second, when it slows down the sound wave it draws out the wave, so it slightly changes the frequency of the note, so it actually lowers the note being played by the speaker making the bass slightly lower.
I would suggest a combination of polyfill, dynamat and carpet.
This will eliminate 90+% of all rattle.
Sleeper,
The slowing down of the backwave by the fiberfill doesn't make it play deeper. In a midrange enclosure, the slowing down minimizes standing waves that can adversely affect freq response. The standing wave issue isn't really relavent in a subwoofer enclosure because any possible standing waves would be well out of the subs playing range. Which brings us to the use of fiberfill in a sub enclosure.
Normally, when a subwoofer plays for any significant amount of time, the VC and motor get pretty hot. The heat is dissipated through the frame and motor assembly into the enclosure. This heat causes the air to expand and increase the pressure in the enclosure making the sub think that the enclosure is smaller than it is which results in a higher Qtc (boomier bass) and less low end freq extension. When fiberfill is added, the tiny fiber vibrate and actually keep the air in the enclosure cooler. The cooler air, keeps the qtc lower which gives you a slightly more effecient system that will have a small advantage in low bass extension.
