From what I've read so far, it seems that if no preamps are used, then using 2 piezos in parallel will improve impedance matching and in turn give better tone and volume. When 2 piezos are used in this way, they are generally the discs.
Would the same effect be obtained by using a piezo rod(under saddle) in parallel with a piezo disc placed elsewhere?
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The piezo rod is several piezos wired in parallel. Each piezo you add cuts the impedance in half. So adding a disc piezo should cut the impedance in half again.
However, if you already have several piezos in the circuit (assuming it's 3 for example), adding a 4th one will have a smaller effect because it's 1/2 of 1/2 of 1/2 or 1/8. So it's going to make it sound 1/8 better.
That all being said, I would be interested in hearing the results of your experiment.
I have now wired the rod and disc in parallel, but added a switch to switch the disc in or out. The result is the switch acts like a gain switch, because not only is it louder with the disc in circuit, but the disc itself has a lot higher output than the rod, so it is hard to detect any sound from the rod when the 2 are in circuit. However, I think the rod contributes subtly to the overall tone, which I think is quite pleasing. Thanks.
So it worked. Kewlsville.
looks like I'll have to. Thanks