On the damping of room resonances with electroacoustic absorbers in the low frequency range

In closed spaces, standing waves occur at low frequencies, thus creating annoying acoustic resonances. Such unwanted phenomena are likely to affect the annoyance of noise sources in the low frequency range. Up to date, low-frwquency treatments are mainly based on bulky devices, such as heavy enclosures. To alleviate this problem, electroacoustic absorbers, namely loudspeakers with shunt synthetic electric loads, can be used to damp room modes and then meet noise reduction specifications. Electrodynamic loudspeakers are good candidates for this type of noise control applications. Their mechanical resonance, typically of the order of tens of Hertz, is within the frequency range where acoustic modes to be controlled. The interactions between these dynamic systems are significant, and a consequent amount of the acoustic energy in the room can be passively dissipated through internal losses in the loudspeaker. This paper investigates the design techniques and experimental validation of electroacoustic absorbers with a view to damp the low-frequency acoustic resonances, in the context of the low-frequency noise reduction in inhabitations.