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We hear this from time to time: Can I wire more than one piezo into the Cortado circuit? Answer: Yes. Add three or four if you like. Caveat: be mindful of phasing! By default, you should be careful that the wires from the metal plates all go to the same input, and the wires from the ceramic spots all go to the same input. By arbitrary convention, we use Red=Metal_Disc=PZ1, and White=Ceramic=PZ2. This works great, UNTIL you stick two discs onto opposite faces of the same resonant surface, like both sides of the soundboard of your acoustic guitar, or both sides of a plate of sheet metal. In this case, the signals the piezos are receiving are out of phase, so to keep the mix sounding natural, you have to switch the phase of one of the discs. Just swap the red and white wires around on the circuit.
We were recently asked about micing the top and bottom heads of a drum. In this case, the two heads are only loosely coupled by the air mass inside the drum, and are usually tuned differently, so I am inclined to say the phasing may be irrelevant. We suggested to this customer that he try micing the drum with the two piezos in phase, then try it out of phase, and see which one he prefers.
