Bass trap

The spectrum of both types can be either narrowed or broadened by design but the generalized difference in bandwidth and tunability dominates their respective performance.

Resonating type bass trap achieves absorption of sound by sympathetic vibration of some free element of the device with the air volume of the room.

Porous absorbers are most commonly made from fiberglass, mineral wool or open cell foam that resists the passage of air molecules through the interstitial space.

Such devices can be enormously effective over their tuned range, but can take up a great deal of space, especially when installed in arrays, and thus are sometimes not a practical solution.

A simple panel resonator can be built to hang on a wall by building a wooden frame, adding several inches of mineral wool to the inside, and fitting a sheet of plywood over the top attached only at the edges.

Approximate full sheet [4' × 8'] plywood panel resonances when mounted on a 1"×4" frame 3.5" deep are: Other common resonating bass traps are forms of the Helmholtz resonator—such as either a stiff walled box with a hole in one side [a port], or a series of slats over-mounted across the face as a stiff-walled box forming narrow openings in the cracks between the slat members.

A bass trap generally comprises a core absorbent damp material, a frame, and a covering for aesthetic reasons.

[4] Bass traps are typically used to attenuate modal resonances and so exact placement depends on which room mode one is trying to target.