(Contact) Microphone to record sound propagation in rocks?

Special Interest Groups Recording Equipment
1

Hi,
what kind of microphone can I use to record high quality sound from rocks (to check sound propagation through it)?

I assume contact microphones are preferred? But within that, which types? What specs?

Any help/suggestion is greatly appreciated! :slight_smile:

Thank you :slight_smile:

2

Apparently geophones mostly operate below 100Hz,
that’s not “high quality” enough for speech or music, just bassy thumps.

3

Thank you @Trebor, I know about them but are totally unsuitable for exactly the reasons you mention. Also they are for the ground not to “stick” on rocks.
What I am looking for (no idea if they exist) are very sensitive microphone (small ones) to “stick” onto a rock or a stone on a building.

The type that (most likely) needs some kind of acoustic couplant (coupling material).

So most likely they are some piezo-like mic / transducer with the front face exposed so it can be put in touch (glued?) with the surface.

Then the rock excitation is then done with small transducer or a small hammer.

Any knowledge of anything along these lines?

Thank you :slight_smile:

4

No idea if this helps: decades ago I got me a simple piezo transducer to experiment with picking up sound from the body of my guitar. It was a dime-size, very thin thingy with a shielded cable dangling, to be connected to an amplifier.
The tricky part would be to get this in solid contact with the rock, without losing higher frequencies (as result of a elastic coupling). The transducer itself should be good enough for picking up higher frequencies if made for guitar pickup.
Just my 5 cents…

1 Like
5

Thank you @Samse26
I did think of that in the first place even before posting but wasn’t sure about the bandwidth and most important about the coupling because of the flat surface of the piezo against the rough rock surface.

How would you couple it?

My understanding is the matching the acoustic impedance is also important?

Thank you for any feedback! :slight_smile:

6

Sorry, as I said, I never used it - but on wood I would just try to make a smooth surface and attach the transducer with some tape. But it would certainly take some experiments under lab conditions if you’d want to find out bandwidth, frequency response etc. to see if this fits your purpose. I can’t offer any experience in this field…

1 Like
7

Thank you @Trebor