THE INFLUENCE OF FREQUENCY SHIFTING ON THE TONE QUALITY OF THE PUBLIC ADDRESS SYSTEM

This paper describes the design of a frequency shifter to suppress acoustic feedback, to be studied by the experimental method. When the frequency shifter is inserted between the microphone and loudspeaker in the public address system, it shifts all frequency components of the microphone signal by a constant amount. By this method two types of distortions due to acoustic feedback in the public address system can be reduced. The sound pressure level in a room can be increased by about 5-8 db on a number of auditoriums. For the public address system in free field, which has multiple loudspeakers, it also has the same effect. If the public address system is operated below but too close to the instability condition the frequency shifter can reduce effectively the interference of the regenerative reverberation.