What causes the increasing echo noise when two calls are open at the same time in the same room?
In: Engineering
It is called resonance. Before the noise in the environment dissipates, that same noise reflects back to the microphone and noise is created again. So same noise, with a small shift, superimposed onto itself. So you have a longer and louder noise.
It is very similar to this: Suppose you are on a swing, giving thrust. You have to give the thrust at the exact moment to add motion to the previous one, othervise your effort won’t be effective. On the contrary, when you give thrust at the opposite site, you would be absorbing the motion.
Resonance frequncy depends on the size of the room (or length of the swing) walls reflecting the energy (sound) back on itself and filling the room with the same thing without dissipating.
If the energy is not absorbed under a certain amount, sound can be increased. Corresponding to the swing where you increase motion to the point where you reach the peak and make a full swing loop.
Volume of the room or circle of swinging is like a battery in this case, collecting the energy like a dam collecting water. There is a wall holding the water at every rain.
A feedback loop.
One microphone picks up the sound of the other devices speaker and amplifies it a little, then it’s played over the speaker and the sound goes through the loop again and again getting louder each time.
Having just one call would cause the same problem (and many propably remember they did) but nowadays the sounds the speaker produced are filtered out of the signal the corresponding microphone picks up by software. This doesn’t work with 2 independant devices though.
First echo triggers a second and third etc. Each echo ends up being echoed again and again.
its basically the equivalent of holding to mirrors up to each other, each echo is picked up and repeated, only limited by how well the microphone can pick up background noise coming from its speaker.
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