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I'm thinking about the possibility of an electroacoustic drum that would be tuned with some kind of RLC circuit.

The drum head would have an electromagnet attached to its center, which would be directly above a small permanent magnet mounted firmly to the sides of the drum. The electromagnet would be the inductor in an RLC circuit.

If I tuned the circuit to some physical mode of the drum head/electromagnet, would I get any coupling between the circuit and the physical drum? Would it be enough to to alter the sound of the drum?

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    $\begingroup$ Might be better to metallize the surface of the drumhead and use it as one of the plates of the C instead of the L, in the same way that condenser microphones work. Or bombard it with high voltage and turn it into an electret? :) $\endgroup$ – endolith Nov 23 '11 at 15:41
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This is only being posted as an answer because I cannot comment (not enough points yet?):

Mark Everitt is wrong... the simplest argument would be appealing to this explanation of a microphone: http://www.ccmr.cornell.edu/education/ask/index.html?quid=1212

You can always evaporate masses to membranes and have them oscillate... this was in fact used in my research to study gravity at extremeley small length-scales.

That being said, yes you can couple a membrane to a circuit. Check out the field of Optomechanics, which does this with laser cooling.

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  • $\begingroup$ Yes, but a microphone is not resonating at the frequency of the membrane. By attaching an off the shelf electromagnet you won't have a drum any more. What you're actually talking about is turning your drum into a speaker. I suppose you could play the sound of a drum through it though. ;) $\endgroup$ – qubyte Nov 22 '11 at 9:27
  • $\begingroup$ BTW, "<name here> is wrong" is a very bad way to disagree with someone on SE. You can "disagree" of course. My answer is written with the assumption that the person asking does not have access to sophisticated evaporative deposition equipment, but rather Radio Shack. $\endgroup$ – qubyte Nov 22 '11 at 9:50
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    $\begingroup$ Evaporated masses were not asked for! He wants to fasten "some RLC" circuit to the drum head. All this wording shows that he read about electroacoustics without really understanding it. $\endgroup$ – Georg Nov 22 '11 at 11:55
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    $\begingroup$ You don't want to spread the mass across the whole membrane, it will destroy the quality factor. It is best to localize the mass at the center (sputtering deposition), and a Kapton membrane is a good material to use. $\endgroup$ – Chris Gerig Nov 22 '11 at 22:58
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    $\begingroup$ @ChrisGerig: If you want me to see your responses use the @-symbol and start typing my name. A box will come up which you should click. This notifies me... You're an actual physicist, and there aren't enough career physicists here in my opinion. The rules may seem silly, but they do work. Think of this as outreach! ;) $\endgroup$ – qubyte Nov 25 '11 at 17:41
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The mass of the electromagnet attached to the drum would ruin the resonance, effectively killing any sound you'd hope to attain. You can check this by taping a small stone to the centre of your drum and hitting it.

What you're making is kind of a speaker. It may be possible to make it light enough not to damage the resonance, but not with a cheap off-the-shelf electromagnet. You may want to consider putting something thin and metallic on top of the drum and suspending an electromagnet beneath it. Experimenting with that may get you an interesting result.

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    $\begingroup$ It's like a speaker and microphone, and a drum of course, at the same time! The thin metal idea is interesting. Why not go the next step and stick a thin metal coil on? Maybe I could somehow cut a piece of aluminum into very thin spirals (like if I coiled a sharp piece of metal up and "stamped" it into the aluminum). Then I could dip it into some insulator and tape it onto the drum head. $\endgroup$ – micahscopes Nov 23 '11 at 8:43
  • $\begingroup$ Is there a particular reason to put the coil on the drum head? It seems like a lot of extra effort compared with the other way around... $\endgroup$ – qubyte Nov 23 '11 at 8:49
  • $\begingroup$ Look at the voice coils used in actual speakers and copy that. They're very light and thin, and thin flexible wires connect the coils to the other circuitry which is not mounted directly to the cone. $\endgroup$ – endolith Nov 23 '11 at 15:39

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