I am a random guy in a garage, and I made a functional laser microphone using random bits of electronics I had in my spare-bits box ($1 laser pointer, old pair of earphones, snip off the earphone and wire in a light dependent resistor) -- admittedly the quality was awful (you could only just make out voices if people in the room talked abnormally loud), but it was great for a fun weekend science project :D

A write-up or vid of the components and build would be interesting..

I would imagine an LDR would be too slow to have a good response to audio.