Make your own Tin Can Microphone. via instructables
Most DIY enthusiasts who are interested in audio gear are familiar with the standard “tin can mic” (or variations thereof), in which a piezo disc is taped onto the bottom of a tin can and then plugged into a high impedance voltage amplifier, like a guitar amp. These types of microphones are nice because they are so easy to make, but they are quite limited in most other areas, including bandwidth, microphonics, signal to noise ratio, impedance matching, and cable driving. These issues usually result in a very noisy and brittle sounding microphone. So out of frustration with these limitations, we created the “New and Improved Tin Can Mic” — the standard tin can mic taken to the next level! Using common household items along with a simple circuit, this mic has a tonality similar to the original tin can mic (for all you Tom Waits fans), but improves upon nearly every other feature. The heart of the mic is the Cortado contact microphone which consists of a tiny phantom powered circuit which creates a balanced output from a piezo disc. This circuit provides a high impedance to the piezo disc, but also provides a low output impedance to match a mixing console input. By properly matching the input and output impedances we achieve a much wider bandwidth than the original tin can mic. The fact that the output is balanced provides a very high signal to noise ratio, and it allows for a long microphone cable to be used without signal degradation.
Another improvement we’ve made to the standard can mic is that we’ve added a styrofoam cup as a mechanical resonator. The cup floats inside of the tin can via rubber bands, which helps keep microphonics and feedback (in live performance situations) manageable. Another benefit of using a floating mechanical resonator is that it’s easy to mod the mic to change its tonality. We can easily alter the resonant frequency of the mic by changing the mass of the cup, or we can emphasize a higher resonant harmonic by adding a vibration node to the cup.