In active acoustics, signals from microphones within a room are processed and fed to loudspeakers in the same room, creating an extended reverberation time and modified room perception. The system’s performance is limited by the audibility and acceptability of colouration at gains close to instability. Some listening tests have been presented in the literature to assess perceptual colouration, but thresholds for when the colouration becomes annoying or unacceptable have not previously been established. In this paper, we revisit the prediction of the gain before instability and show how this can be used to equalize an active acoustics system. Then, we present new listening tests where listeners were asked to rate the audibility and annoyance of changes introduced by 8 channel active acoustics systems in two rooms at various simulated gains. We show that the annoyance depends on the initial room acoustics as well as the loop gain; perceptual thresholds for slightly annoying degradation varied from?5.4 dB to ?8.5 dB, relative to instability. These thresholds are discussed in the context of objective measurements calculated from the impulse responses. The resonance perception is linked to the gain where the reverberation time starts to grow much more quickly in some frequency bands than others. It is also shown to be well predicted by the standard deviation of the magnitude response, with a value of 0.62 corresponding to slightly annoying degradation.
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