Here is the premise. If you hook up a speaker to a microphone input, the speaker magically becomes a dynamic microphone. A speaker uses an electromagnet to move a paper cone forward and back, which moves the air forward and back, which we perceive as sound. Thanks to the magic of electronics, if you move the cone forward and back, it will output that signal as well. So by using the air moving off of the resonant bass drum head, that same air will move the paper cone of my speaker, which I will use to record.
For my speaker of choice, i have a stock Delco 6" speaker out of my car. I used some rubber bands and a fan from a server as the stand since it's just the right height.
it's very thrown together, I know. Anyway, the speaker did not have + or - terminals marked, so I had to phase-match it with a known speaker. For that I busted out my trusty old Bose POS. I rigged up the wiring to piggy back off of the Bose's, and then touched my "mic" terminals with either end, switching back and forth. When the two speakers are right next to each other and the speakers are in phase, the music will sound very clear and concise. When they are out of phase, it will sound, well, weird and funky and not very loud. When i found the correct phasing i tightened the little butt crimp terminals and enjoyed some music.
Here's the piggy-backing:
When i was happy with the sound I set the whole thing up against the bass reso head. The trick here is to get the speaker as close as possible to reduce the airy loss. To test it, i kept playing my test track through the speaker and moved the speaker around the bass head. Listening to the resonance in the bass head (specifically its volume) found me the strongest spot on the head, so that's where I put the mic. The paper cone itself is about 1 cm away from the head (the metal basket has lips that stick forward by about .5 cm)
The best part is AUDIO!!! so here you go.
http://www.youtube.com/watch?v=JEmmTQk0I4E
