Howling remover having cascade connected equalizers suppressing multiple noise peaks

A howling prevention apparatus for preventing a howling noise generated in an amplification loop, the amplification loop including a sound collector for collecting a sound to be produced, and sound producing means for amplifying the sound collected by the sound collector and for producing a sound, said howling prevention apparatus comprising:

• a plurality of equalizers each having a variable frequency response, and being coupled in series to one another between the sound collector and the sound producing means;
• a detector for supplying a noise signal to said sound producing means to enable said sound producing means to produce a test sound and for measuring the test sound collected by said sound collector through said equalizers to thereby detect a plurality of frequency points at which a loop gain of the amplification loop reaches a peak;
• and
• a circuit for successively setting the variable frequency response of each equalizer to suppress a noise peak at and around each frequency point detected by said detector so that the plurality of the equalizers are individually adjusted to suppress the respective noise peaks to thereby prevent the howling noise, wherein
• said detector comprises a band pass filter having a variable center frequency and being coupled to the plurality of equalizers, and at least one stage of a low pass filter cascade-connected to the band pass filter and having a cut-off frequency variable in a specified relationship with the center frequency, and a circuit for stepwise sweeping the variable center frequency of the band pass filter so as to detect the plurality of the frequency points.