Most any speaker can be used for a microphone. A speaker is a very similar concept compared to a microphone, it just works in reverse. I large speaker only does a good job of capturing low freqencies. Yamaha actually sells a speaker that is intended to be used as a kick drum mic! The small earbuds will pickup a wider frequency range than you would think. I wouldn't use an expensive set of earbuds though, as I have no idea if the plug-in-power does any damage to the headphones...