Well I am making a play and we are using proper microphones on amplifiers and whenever we put it upside down or get to close it squeals and fills the room with a high pitched noise that kills everyone's ears any ideas to help us prevent it ,
this is called a feedback loop. whats happening is your microphone is picking up the speakers its outputting on. so you talk in to the mic, it comes out a speaker, the mic picks that up and amplifies it again, it comes out the speaker again and the mic picks it up again and on and on and on. this is why radio shows tell you not to try to listen to yourself when you call in, because your phone will pick up your own voice and create a loop.
simple fix, dont play your own voice back through a speaker the mic can hear.