What is the best "stuff" to fill a speaker cabinet with?

The following discussion will focus on practical facts on speaker cabinet stuffing and on sealed systems. Theory is limited help in selecting speaker stuffing. Vented system do share a few of these same issues and will also be mentioned, but the goals and physics of stuffing a vented box are different than those of a sealed box. NHT speakers use polyester fill. Some use a Danish polyester that mimics the properties of fiberglas very closely. Excluding this special poly, there are two kinds of polyester available: pillow stuffing, and audio-spec polyester. Forget pillow fill. It's cheap and easy to get. If you use enough, it will damp the midrange, and that's a lot better than an empty box. But it has little effect on lower frequencies. Some fabric stores sell "Super Good Stuff" from Stearns Technical Textiles. This is a common, inexpensive material that is said to perform as well as audio-spec polyester. For lining the walls of a vented enclosure to reduce internal reflections, or ...  more