Peizo can be delicate. I find that the soldering point of the peizo stick would be the most finicky part. That is why I opted for the sticky copper wire instead of soldering iron. It is still prudent to check the integrity of your peizo after the cutting and wiring. I find 440Hz is effective frequency for this purpose. After the cutting and putting a copper part underneath the peizo disk, any movement generated by the peizo would be reduced greatly. If we apply 20V to the peizo, too low of a frequency, you can't hear a thing, too high of a frequency, it would generate nasty sound and damage your ear. 440Hz, the central C is best.