Bass Trap
An acoustical treatment designed to absorb low frequencies and reduce amount of low frequency energy that is reflected back into the listening room.
This in-turn will reduce the severity and intensity of standing waves or “room modes”, which can create an uneven bass response from the subwoofer.
Bass traps are generally large (because low frequencies have long wavelengths which are difficult to trap) and are typically constructed of damping material like mineral wool or fiberglass.
Bass traps are normally placed in the corners of a room, where low frequencies naturally build up.