What causes that howling sound in PA systems?
A simple PA (public address) system consists of a microphone, an amplifier and one or more speakers. Whenever you have those three components, you have the potential for feedback. Feedback occurs when the sound from the speakers makes it back into the microphone and is re-amplified and sent through the speakers again, like this: Imagine, for example, that you place the microphone in front of the speaker as shown. Now you tap on the microphone. The sound of the tap goes through the amplifier, comes out the speaker, re-enters the microphone, etc. This loop happens so quickly that it creates its own frequency, which we hear as a howling sound. The distance between the mike and the speakers has a lot to do with the frequency of the howling, because that distance controls how quickly the sound can loop through the system. You can actually try this out on your comput
