Experimental assessment of active electroacoustic absorbers for broadband room modes damping

Active electroacoustic absorbers are membrane absorbers actuated, through a feedback control loop and an electromechanical driver, so as to present optimal sound absorption on a broadband range around the membrane resonance. Taking advantage of the low resonance frequency of conventional loudspeakers, this technique appears as an interesting solution for the damping of low-frequency modes in rooms. This concept has direct applications to real life problems, such as the equalization of sound diffusion in the low-frequency range, or the mitigation of noise immission from external noise sources in habitations, among others. The performance of 4 prototypes of active electroacoustic absorbers is assessed inside a reverberant chamber with different sound stimuli (stationary broadband noise, pure tones). It is shown that the 4 electroacoustic absorbers prototypes, which represent only 0.1% of the total wall surfaces, achieve a global noise level attenuation of almost 8 dB, on a broad frequency range from 20 Hz up to 100 Hz, with individual mode attenuations up to 12 dB. Moreover, the modal decay times are significantly reduced, which is also verified with recordings of time-limited pure tones at several resonant frequencies in the room.