Demonstration of Acoustic Damping

Author: N.H. Crowhurst

For this reason, the best way to achieve good operation of a loudspeaker is to damp its movement acoustically by attention to the construction of the loudspeaker enclosure. This can be illustrated quite effectively by mounting a loudspeaker in a simple enclosure with three alternatives for the back of the enclosure.

Enclosure construction affects speaker response

A completely, open back results in a load on the diaphragm that acts as a mass or weight of air moving bodily. A completely closed back makes the air inside the cabinet act as a compressible cushion. Using an acoustic resistance consisting of a large number of holes that allow the air to pass through but offer resistance to its passage achieves an intermediate condition that damps the diaphragm properly.

Comparison of results shows that the response is much smoother with the acoustic damping and that under this condition, electrical damping becomes unimportant. With either the solid or the open back, electrical damping from the amplifier makes a considerable difference to the response of the loudspeaker, but neither performance is as good as that with the acoustic resistance.