What causes the screeching feedback when you’re on the phone with someone who is in the same location?
When your voice transmits through a phone, it gets a little bit distorted. Some of that distortion causes it to be slightly higher pitched.
If the sound comes back to the original phone it will transmit again. Again, it is distorted. Now it’s been distorted twice. If the phones are close enough, this keeps happening again and again. The sound goes back through and gets even more distorted. After awhile, it just sounds like a horrible high pitched whirring noise.
If you have two phones close together you can start the feedback by talking into one of them. If they are super close together, even the small background noise might be enough to start it.
Think of the phone as playing shadow, but It doesn’t repeat, it just tells the other phone what to say out loud. So if a dog barks, phone 1 is telling phone 2 to bark. When the phone 2 barks, and both phones are in the same room, phone 1 hears it, and again tells phone 2 to bark. At the same time, phone two is doing the exact same thing to phone 1 – sending bark and hearing barks. Pretty soon, all you hear is a bark on top of another bark on top of another bark (even though there was only ONE real bark to begin with). In real life, you don’t just get barks, you get every noise that’s happening in the room multiplied over itself. That’s the screeching feedback.
Its a phenomenon called “Larsen”.
It is caused by a feedback amplification of the sound between a microphone and a amplified speaker. To experience it, you only need to have a microphone that plays its recorded sound “live” in an amplified speaker.
What happens is the sound caught by the microphone is played (loudly) by the speaker and is caught again by the microphone, causing an “infinite loop” of sound, that we percieve as screeching.
The same sound starts looping back and forth between the two devices, the higher pitched noises are amplified with more strength than the lower pitch noises so on each loop the noise getting passed is higher and higher pitch until it becomes unpleasant.