Sound trigger for high speed flash photography, part 2

Though still not perfect, my circuit is getting a little better.  I removed the second capacitor (C2) from the original circuit design.  The new design can detect slight air vibrations (e.g. when I blow on the electret microphone) and softer sounds (e.g. light finger snaps).  Water drops cannot be picked up still however, although I can hear the plop that it makes.  I guess it is just a matter of increasing amplification.

Now, the idea behind the LM324 op-amp that I am using is this:  the op-amp amplifies the voltage difference between the V+ input pin and V- input pin.  (See:  http://en.wikipedia.org/wiki/Operational_amplifier.)  The V+ input would be used as a reference voltage.  The V- input would be fed from the electret circuit.  Increasing the resistance of R5 or decreasing R2 should increase the amplification.

I have tried decreasing R2 to zero but it does not seem to change the sensitivity of the circuit--from my visual observation.  R5 is already set at 1 MOhm.  Maybe I can get a 10 MOhm resistor and see what happens.  Intuitively, increasing R5 would allow more current to flow to the output line and less to the V- input line (i.e. the negative feedback).  Similarly, decreasing R2 would allow more current to flow into the V- input pin of the LM324.

I will see if I can find some time to swing by my local electronic store to pick up a 10 MOhm resistor some time this week.