I've seen this following post regarding using the speakers as a microphone: https://skeptics.stackexchange.com/questions/5664/can-a-computer-be-hacked-to-use-a-connected-speaker-as-a-microphone
There are some things I don't understand about it. He says that an amplifier doesn't pass any signal from it's output to it's input. Is this correct? if I have an amplifier such that output=100*input and I force 100*x on the output, won't I get x in the input?
To my understanding, speakers are always plugged through an amplifier to the sound card. The question is whether the amplifier resides in the sound card (where it is also controllable and we can lower it) or in the speaker. In any way, say that when I produce a voltage of x from the sound card I get some sound signal level in the air of gx right on the speakers (g in the appropriate units). Now if I produce a sound in the air that is equal to gx right on the speakers I will get the voltage level x to the sound card. So reducing the amplifier is just a matter of reducing this g. Is this the accurate explanation? and not the explanation inside the link?