Acoustic feedback (also known as howling) is inevitable whenever sound reinforcement is necessary, for instance
in large meeting rooms, court rooms, classrooms, auditoriums, theaters, etc. In such large rooms, although audience
(or participants) are seated in the same room, they may be seated far from the presenter (or from each other) and
may not hear the message clearly.
Sound reinforcement is necessary in such situations where microphones
are used to pick up the talker voice, the microphones signals are amplified, and then played to loudspeakers placed
in the same room so that audience can hear clearly. The problem, however, is that the microphones not only pick up the
presenter's voice, but they also pick up the loudspeaker sound after traveling through the room back to the microphones,
causing a closed electroacoustic loop. If the loop gain at any frequency becomes larger than 1, the loop becomes
unstable at that frequency, and starts oscillation, producing the well known howling phenomenon.