Towards an active reverberant room

A laboratory reverberant room is used for sound power, sound absorption, and sound scattering measurements, and needs to meet certain volume and absorption criteria in order to make good measurements. This paper examines the possibility of creating or enhancing a reverberant room through a system of electroacoustic feedback. For such a system, signals from a set of microphones could be distributed to a set of loudspeakers, with the system’s transfer functions between microphones and loudspeakers (i.e., the gain, delays, and detailed spectrum) established so as to create desired exponential decay of the total system as sound feeds back through the combined physical space and electroacoustic system. Such an approach might increase the spatial diffusivity of the reverberant soundfield, increase the modal density of a room (by introducing new modes that have an electroacoustic component), and increase reverberation time. Experimental results using a simple feedback system in a rectangular reverberant room yielded potentially large changes in reverberation time, and, with careful tuning, allowed the room’s magnitude response to be increased at frequencies where its natural response is weak.