Howling is one of the most annoying problems for public-address systems in a reverberant sound field. A new technique to suppress howling has been developed, in which the direction of the strongest coupling between the microphone and the loudspeaker is constantly detected to lower the sensitivity of the microphone in that particular direction. For detecting the direction of coupling, a reference signal, whose spectrum is modulated to spread over the frequency range of the public-address system, is combined with the acoustic input to be reproduced from the loudspeaker. This combined reference signal is eventually picked up by an array of microphone units. The direction of the coupling is detected from the difference in the arrival time of the reference signal between these microphone units. To lower the sensitivity of the microphone array for the particular direction, the directivity of the microphone array is controlled by individually delaying the outputs of each of the microphone units and then combining them as the output of the microphone array.
The problem in the sound quality evaluation of loudspeakers using their frequency characteristics is that the sound quality difference perceived by human ears is not distinctly represented in the frequency characteristics. To solve this problem, an evaluation method using the Wigner distribution that is derived from the impulse responses of loudspeakers is employed. The effectiveness of this evaluation method in comparison with conventional frequency characteristics was examined using two loudspeakers with clearly different sound qualities. While there was no noticeable relationship between the frequency characteristics of the loudspeakers and listener's subjective impressions, the Wigner distributions showed a recognizable correlation with listener's subjective impressions. Thus it can be concluded that the Wigner distribution can represent the sound qualities of loudspeakers more effectively than conventional frequency characteristics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.