Eventually the system starts to ring, and keeps howling until the volume is reduced. The right microphone will reduce the problem. A microphone without peaks in its response is best, as feedback will occur most easily at the frequencies where peaks exist. While a good omni might work well in some situations, a cardioid is almost always preferred where a high potential for feedback exists.
Distance is also a factor.
Bringing the microphone closer to the intended sound source will also help. And in general, the microphone should always be located behind the speakers. This happens, for example, when two microphones are placed on a lectern as in Fig. Because they are spaced apart, sound from the subject will almost certainly arrive at the two microphones at different times. The curves in Fig.