Study on room modal equalization at low frequencies with electroacoustic absorbers

Nowadays, requirements for acoustic treatments in rooms are ever more demanding in terms of performance and compactness. A recurring issue in closed spaces is the occurrence of standing waves and acoustic interferences at low frequencies. These unwanted phenomena are likely to affect the frequency response of rooms such as offices, concert halls or home theaters. Unfortunately, state-of-the-art soundproofing solutions cannot efficiently dissipate sound energy, or their embodiments are so bulky that they become almost impracticable. To that purpose, electroacoustic absorbers employing direct-radiator loudspeaker systems can be used to improve listening quality and meet the specifications. Electrodynamic transducers are obvious candidate for this type of noise control application. They are controlled by the resistance around the mechanical resonance, typically of the order of a few tens of Hertz, which also lies in the frequency range of acoustic modes to be damped. This results in a strong interaction between both dynamic systems from which part of the incident acoustic energy of the sound field can be dissipated. A specific electrical load is also connected across the transducer terminals in order to further improve the passive dissipation through the internal damping within the loudspeaker. This paper investigates an optimized placement of electroacoustic absorbers in a reverberant room in order to damp the lowest acoustic resonances.