On Tone Colouration through Acoustic Feedback in Public Address Systems

The work describes the incidence of tone colouration in back-coupled public address systems whose loop-circuit-amplification is not very small in comparison with the value which arises from self-excitation. The overlying theory is described, simulating the steady state responses with a digital computer as well as the results of the measured threshold amplification for tone colour from hearing research investigations. The absolute perceptible threshold for tone colour amounts to about − 12 to − 13 dB, the threshold for distinct tone colour in speech is about − 5 dB, both being with respect to the critical loop amplification of self-excitation.