For some units, it is desirable to have suspensions that are pliable enough to let the woofer cone travel freely in and out. A technical specification for this characteristic in more expensive speakers, is XMS . The further the cone can travel and the more compliant it is, the stronger the bass can be in enclosures that take advantage of it. However, certain types of very good enclosures require a more limited, stiffer cone movement to develop their more controlled and High Fidelity response. Surrounds are usually made of cloth, foam or rubber.
Rubber tends to last longest.
Super Tweeter A Driver constructed to reproduce the highest possible frequencies from roughly 13 kHz to 25 kHz. Supraaural Term used in reference to headphones. Supraaural phones rest on the ear, rather than enclosing the ear. Supraaural phones typically are lightweight, and because they do not seal around the ear, tend to not provide good isolation, but permit the listener a higher degree of awareness of external sounds.