General Sealed boxes

no a box can be any shape and dacron is a brand of fiber fill used to slow the waves down in a box to make the sub think the box is bigger.

The reason they are made trapezoid is to prevent standing waves - The angled baffle prevents waves inside from bouncing around as easily. A rectangular box can work well, but should be well damped./NyxBass

if the side of the box containing the driver is parallel to the side opposite teh driver, the sound waves will reflect off of the opposing surface, and cancel themselves out. This is called standing wave cancellation. It's a very bad thing.Angling one of the two sides will prevent this. Adding polyfill does a similar thing by giving more surface area of a non-parallel nature from which the waves can reflect. Ployfill also has the added benefit of making the box seem larger than it rally is to the driver(s)Dacron is a commercial name for a synthetic fiber. It's what polyfill is. Pillow stuffing.While you can make a square box, most times it doesn't work as well, and you need to do tricks to it so its not parallel inside the box, like lining the enclosure with "egg-crate" foam.-GlassWolf

Pioneer Stage-4, Orion, DynAudio, Fi