A sound system in a room forms a closed electroacoustical loop which may oscillate or howl at frequencies for which loop parameters meet certain criteria. In an experimental program, carried out in both reverberant and well-damped rooms, howl points were determined by direct measurement of loop gain and phase. The results agreed well with those obtained by causing the system to howl spontaneously. The number of howl points present at a given gain level and the effects of air temperature and microphone placement were explored. The results have a practical bearing upon sound system design and equalization.
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