With the Eyecam we have 4 microphones, by mounting them in different directions they could record different types of waves.
Put them inside a sealed anechoic chamber that is solidly connected to the ground.
A network of them could detect the direction and speed if time stamped.
Yep piezo's are brittle, used to use them for Combine Harvester wheat/chaff separation percentage tracking.
Ceramic turntable elements, tricky little things to mount on the sensor plates and they would snap if you touched them too hard.
Once sealed in the plates they a lasted long time, but they were designed to be easily replaced.
Very low cost
Analog DSP with opamps/filters/comparators, hate to think about coding that these days.
Job after that was Ground Vibration monitoring for Mining ( explosions) and civil constructions.
3 separate velocity sensors (coil/magnet based), much more expensive and you learn to build tough, trucks ran over these things
Very weird, you could make them waterproof but outback bulldust still got in
Next job - PC/DSP based Predictive Maintenance using vibration analysis on rotating machinery.
Heavy iron -TI DSP and PC MS C coding, graph plotting etc.
Pi's could do these things much cheaper now, coding simpler too, plus many more features and a bit more than 32KB or 640KB of sram:D
Still pretty early days for Pi's in Science, starting to appear in Journals/Thesis etc
Still waiting for the Officially approved SciPi Guy T Shirts
I'm dancing on Rainbows.
Raspberries are not Apples or Oranges