Assessment of active electroacoustic absorbers as low-frequency modal dampers in rooms

In small to medium size rooms, natural room modes may severely strengthen the annoyance of low frequency noises, such as traffic or equipment noise. Moreover, there is an actual technological gap in the state-of-the-art concerning low-frequency treatments, and the only potential solutions basically take the form of heavy and bulky bodies. With a view to develop such low-frequency solutions (with compactness requirements), the concept of “shunt loudspeaker” has already been demonstrated to provide controllable electroacoustic dissipation to tackle one or a few modes around the loudspeaker resonance (in the low frequency range). The present paper extend this study to the concept of “electroacoustic absorbers”, based on the connection of loudspeakers to individual synthetic active electric loads, capable of achieving broadband sound absorption around the loudspeaker resonance, up to almost 200 Hz. This paper will especially investigate the optimization of the design, as well as discussion on practical spatial arrangement of electroacoustic absorbers, in the context of an experimental assessment in a test room, so as to provide significant damping of the low-frequency acoustic resonances in the [20-100 Hz]. The resulting modes attenuations range from -1dB to -14 dB along the bandwidth of interest.