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There is a formula to calculate the amount of poly fill to stuff. Without getting into the electro mechanical formulas, use of compressed poly fill effectively increases the box volume that the driver sees. I seem to remember 1 lb polyfill increases effective box volume by 1/2 cubic foot (not sure but will have to look that up as I don't seem to remember it.) This is no free ride however because it effectively increases the mass of the driver and more difficult to control, more ringing and distortion in performance applications. It is critical that using compressed polyfill in a very small enclosure that choosing a driver with the lowest mass (mmd) for the desired F3 you are going for. For those guys who like to crank on numbers, check out these two books
Martin Colloms- High Performance Loudspeakers and Their Enclosures.
Vance D i c kenson- Loudspeaker Design Cookbook.
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