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Well, I was just going to put a contact mic in my cellar. My understanding is that this is the best way to pick up low-frequency vibrations. I know very little

by dmazin 2y ago

Well, I was just going to put a contact mic in my cellar. My understanding is that this is the best way to pick up low-frequency vibrations. I know very little about audio engineering. I wonder what else I might be able to use to pick up the vibration signature? I completely understand your drive to pick up those high-frequency vibrations! There's a whole secret world of vibrations out there, and we can analyze it!

jbl0ndie 2y ago
You might struggle using microphones if it's very low frequency because most human audio microphones intentionally filter frequencies that are below (and above) human hearing range. Perhaps fixing to he contact mic to the right resonant object might serve to translate the low frequency to a higher frequency? Could you use the accelerometer on a smart phone to 'hear' the vibrations?
- dmazin 2y ago
  I don't know if a contact mic really has any filtering though; it's just a piezo element that I plug into a pre-amp. However, what you're saying is completely legit. I read that I might want to lay a large, sturdy thing on the floor and put the mic on that, for the same reason that you gave. I used a large old pane of glass that I found in the cellar.
  - cruffle_duffle 2y ago
    All that came to my mind is making sure to physically bond it to the floor. But then you still need to have something that moves relative to the magnet and then I got confused again. What do seismographs do? People also use acoustic pings to measure soil and rock density underground. What are those devices using for their “microphone”? And yeah, would an accelerometer work? I don’t know what the temporal resolution is on your standard Amazon / AliExpress accelerometer is but it’s probably pretty decent?
myself248 2y ago
"Geophone" is the device you seek. Amplifying and digitizing the signal is straightforward for an experienced EE, but you might look into acquiring some Raspberry Shake hardware which has it all already done.
- dmazin 2y ago
  Oh, snap. Thank you. Guess I’m about to be $350 poorer!

by dmazin 2y ago

jbl0ndie 2y ago

You might struggle using microphones if it's very low frequency because most human audio microphones intentionally filter frequencies that are below (and above) human hearing range. Perhaps fixing to he contact mic to the right resonant object might serve to translate the low frequency to a higher frequency? Could you use the accelerometer on a smart phone to 'hear' the vibrations?

dmazin 2y ago
I don't know if a contact mic really has any filtering though; it's just a piezo element that I plug into a pre-amp. However, what you're saying is completely legit. I read that I might want to lay a large, sturdy thing on the floor and put the mic on that, for the same reason that you gave. I used a large old pane of glass that I found in the cellar.
- cruffle_duffle 2y ago
  All that came to my mind is making sure to physically bond it to the floor. But then you still need to have something that moves relative to the magnet and then I got confused again. What do seismographs do? People also use acoustic pings to measure soil and rock density underground. What are those devices using for their “microphone”? And yeah, would an accelerometer work? I don’t know what the temporal resolution is on your standard Amazon / AliExpress accelerometer is but it’s probably pretty decent?

myself248 2y ago

"Geophone" is the device you seek. Amplifying and digitizing the signal is straightforward for an experienced EE, but you might look into acquiring some Raspberry Shake hardware which has it all already done.

dmazin 2y ago
Oh, snap. Thank you. Guess I’m about to be $350 poorer!