What's the noise of the loudspeaker?
It's possible that the audio is out of range and that there might be some problems with the headset
You may be the microphone and the microphone was too near '
The amplifier input end is connected with a microphone? If yes, the acoustic feedback phenomenon between the speaker and microphone, there was a "howling", and the principle of self-excited circuit is the same. When the input or output (i.e. microphone or speakers) signal intensity decrease or change the direction, the acoustic feedback condition is destroyed, this phenomenon will disappear.If the amplifier produces nearly "ultrasonic" range of voice Scream (because in ultrasonic frequency band sound the human ear can not perceive, hear is probably low harmonic this "ultrasonic" band amplified sound), it is possible that the low frequency circuit (usually audio amplifier) produce a self-excited the phenomenon, if not treated, may cause damage to the amplifier.
The loudspeaker made a shrill noise, a howl.The self-excited feedback of the amplifying system is that the feedback loop is positive feedback, and if the microphone signal is modulated by phase, it will destroy the self-excited phase condition, thus preventing the system from self-excited whistling.The microphone and microphone have the best stability when the phase deviation is 140 degrees; and the higher the modulation frequency, the better the system stability. The maximum allowable value of the phase modulation frequency is 4Hz in order not to cause too much distortion in the processed sound quality.
