Using two piezo contact microphones sandwiched together makes for an easy noise free balanced contact microphone.
I have explained this pretty well in this Instructable.
![](https://christian.liljedahl.dk/content/images/2020/01/Balanced-Microphone-Correct-polarisation-correct-colors.jpg)
![](https://christian.liljedahl.dk/content/images/2020/01/image002.jpg)
![](https://christian.liljedahl.dk/content/images/2020/01/image001.jpg)
Using two piezo contact microphones sandwiched together makes for an easy noise free balanced contact microphone.
I have explained this pretty well in this Instructable.