Use of Selective Equalization for Feedback Suppression

The paper summarizes results of measurements and observations made in about 200 rooms with sound re-enforcing systems. Behavior of sine-wave room response near major feedback modes is described. The effect on feedback of broad-band equilization is shown. The role of narrow-band filters relative to control of ring modes and excessive reverberation is set out. The existence of a limit to system gain before feedback, set by the geometry of the situation and other parameters, is discussed, along with the concomitant change in the nature of the feedback modes as the limit is approached. The observed effect of temperature on the frequency of feedback and ring modes is reported. The degree of nonlinearity between the irregularity of room response at these modes and the insertion loss of a filter to eliminate the irregularity is described.