Sound absorbers with tunable resonance frequency

Purpose

Development of small-size sound absorbers with a tunable resonance frequency for reducing the levels of infrasonic and low-frequency air-borne noise in rooms. The resonance sound absorbers are most efficient when used for the suppression of higher levels of discrete components in the spectrum of noise with elevated levels.

Structure of the sound absorbers and the principle of their operation
Prototypes of resonance absorbers: two versions
Prototypes of resonance absorbers:
two versions

 
Sound absorption coefficient of a resonance sound absorber with a diffraction screen
Sound absorption coefficient of a resonance sound absorber with a diffraction screen;
the sound absorber is tuned
to a frequency of 120 Hz

Structurally, the sound absorber is a resonator whose acoustic parameters are controlled by modifying the resonance cavity. In the two versions of sound absorbers that were developed, the resonance frequency is controlled by varying the position of the diffraction screen or by varying the length of the air ducts connected with the resonance cavity volume.

Degree of readiness

A technique is developed for the design and the calculation of the parameters of sound absorbers with the resonance frequency from 10 to 500 Hz. Prototypes of two aforementioned versions of sound absorbers are manufactured. A test bench - an acoustic interferometer - is designed. By testing the sound absorber prototypes with the use of the test bench, it was found that the effective sound absorption coefficient was no less than 0.8 in the 1/2 octave band relative to the resonance frequency.

The results of all preceding work make it possible to design pilot resonance absorbers and to develop the technology for their mounting in various specific rooms.