Pressure Sensor/Actuator on drum head.

So I was watching this video:

http://www.youtube.com/watch?v=chhxK_RhZIk

And in addition to being mind-blown. I was inspired to make something similar.

Theres 2 vids, and it shows some different sounds in the 2nd one (high frequency resonance).

From what I can understand in the description and wikipedia page (http://en.wikipedia.org/wiki/Feed-Drum) for it, it looks like some kind of sensor/actuator is doing all the work.

It says the head is "electronically conditions" and that the signal is feed back to it via "acoustic pressure". It looks like maybe some kind of pressure sensor? But I've not seen any so thin/intricate/durable (he's whacking the hell out of that drum!). As far as the feedback part, I'm confused there too. There is no bottom head on the drum, and the drum is massive, so that kind of rules out a big speaker inside of it, or something simple like that.

Does anyone have any idea what's going on there?

generated by a feed-back system that sampled the signal issued by a piezoceramic sensor placed on the rim

piezo's are quite often used in drum kits, looks like he is just playing some physics tricks to change the experience

items with piezo electric capability generate electricity when pressure is applied

How is it so particular when it comes to specific placement? It seems like a millimetre in any given direction (along the lines) has an impact on the sound.

Or are you saying the piezo is what's vibrating the head?

I believe its the thing hanging off the side of the drum, kinda looks like a old mic casing

but its pointed directly at a point, when the drum is struck in different places the resulting wave on the drum head comes in at different strengths and angles, which is being picked up my the mostly focused unidirectional peizo

I think, that is probably where I would start, its picking up waves running it into a feedback loop and outputting it to (something, I haven't gotten that far)

I think the mic is just that, a mic. When the drum is wiggling around, the mic stays stationary, which probably means it's on it's own stand.

That did make sense about the waves/nodes and a piezo. The wiki article gets pretty heavy into math, so I'm assuming that's a big part of it. The nodes/partials of the drums influencing how it resonates, like harmonics on a stringed instrument.

He appears to have some kind of control system to his left, as you can see him messing with it around the time he starts doing high frequency stuff in the second video: http://www.youtube.com/watch?v=G41JGAYsgsg at 8:23 in he reaches over and adjusts something.

It mentions using a piezo on the rim, which seems odd to me. I would think the head would be a much better place to 'hear' the frequencies, but I suppose it might dampen the head a bit, having it on there. It does say a speaker is what excites the head. I'm guessing just the low frequency stuff, and the head being 'tuned' by choosing the nodal points is what whole mechanism.

Hmm. I know the arduino can handle 'lo-fi' audio. I wonder if a self-standing version of this system could handle with an arduino (analysing the input frequency and generating a signal to be feed back into the system).

more realistically you would use the arduino as a microcontroller, IE a interface to the physical world and let your pc do the heavy lifting

there's quite a bit going on, drum physics, piezo's, synthesis, and analog feedback amplifier loops, along with some serious low frequency driver, maybe akin to what I used to install on top notch church organs (one installation used to have the nasty habit of popping open the fire-door in its room sized enclosure, but thats way off topic)

Just taking a quick look, I'd say he uses a microphone to capture audio from the drum, then conditions the audio thru a self damping feedback circuit to a lower frequency outside our normal hearing range, then feeds this back inside the drum using something similar to a base cannon speaker. this vibrates the drum head such that the drum sticks will vibrate on the top of the drum head. So basically he is probably using sub audio frequencies to vibrate the drum head.

It does look like it's going to take a some proper computing to get it going. At least I've got a bit of a handle on how it happens now.

Such an amazing instrument/sound too.