Before we started, we considered trying the following experiments:
We obtained:
Experimentation
We started by building the circuit. As we went we got a lot of circuit debugging experience! We learned the truly inifinite benefits of the multimeter.
We then moved on to the headphones. We had two pair, one to use for the actual headphones and one to use just for the wiring.
So, for the use of the microphones, we had to sacrifice a pair of (cheapo) headphones. We put them on a stool and said some kind of chant, holding them above our heads. Then we snipped the wires. We found that each of the left and right headphones had two wires going to them, one being ground and one being the signal, of course. We then soldered these wires to the mics.
As you know, we were using low-quality headphones, and when we mounted the mics on the outside of the headphones, we got little beneficial effect. We found that we could get better results using nice headphones, but they still were not very effective. We moved mics inside headphones to decrease sound delay effects. This greatly improved performance, but introduced feedback until we rigidly pointed the mics away from the headphones' speakers and covered the mics with headphone foam (from the pair of headphones that we had to sacrifice).
Soon, we were doing our best to make the whole system work. We found that due to sound propogation delay, non-inverted output (in our case) produced better effect than inverted output. We also observed that headphones were ineffectual for high frequencies, so to reduce noise produced by the circuit, the input was put through a simple RC lowpass filter with Wo=1K.