Using contact microphone for vibration detection and audio sampling.
I used contact microphone (piezoelectric mic) mounted in the middle of the glass window, to detect vibrations from nearby house renovation. I wanted to take few samples of everyday things to create a library of FFT to later match with live feeds in similar way a sonar operator onboard any vessel will match using hydrophone to identify other ships and submarine at sea.
Warning! This setup involves recording audio of surroundings which might include other people. Make sure to follow your local government laws and regulations regarding privacy of others.
Setup is simple, contact microphone and audio interface was bought from Amazon. I used audio interface to have more control over audio input the normal built-in audio jack in laptop. I used Spectrum lab for visualise audio and recording.
Contact microphone is a piezoelectric mic with suction cup to stick it to glossy surfaces. It normally sold as Guitar pick up mic.
Contact microphone was connected to a laptop running a Spectrum Lab via USB audio interface.
Below is a sample FFT captured from contact microphone.
In this sample an air compressor was running, a jack hammer was used followed by hand hammer.
73.