Detection of mechanical damage using microphone & DSP

[pwok]

Hello,
I'm looking for information about "How to detect mechanical damage using microphone". I know, that the Professional devices uses ultrasound sensors but I think that simple microphone and DSP can do this too.

First We need an audio signal, amplitude, FFT of well working machine. When We measure in real time, We can subtract this old signal from new one. I think it could work with engines. But what do You think about suspension. Different textures of road, roughness, bumps. Is it posiible?

Thanks for answers.

 

[StupidStudent]

what about the precision? 'ordinary' audio signals has long wavelength... so I think, in my opinion, it cannot detect small c-r-ac-k [why this word censored by **** anyway?] and textures. But maybe it works on large objects. CMIIW