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Of course in space there is no sound transmitted via air, so there is no air-borne sound, but there is structure borne sound. This sound can be recorded with a pickup microphone, but do pickup microphones need air to work as well?

Considering that a pickup is really just recording the surface waves, but if it is mounted on the same surface with the same vibrations, it in theory should measure nothing, correct? My assumption is that pickups measure the difference between the air damped surrounding and the material itself, so it should not work in vaccum as there is nothing to damp against.

The other theory I have is that it depends on the mounting of the microphone. So if I fully connect it in a sphere around a certain point, it would measure the surface wave within this mounting area, but wouldn't that limit the measurement to sound waves smaller than the mounting area (higher frequencies)?

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  • \$\begingroup\$ what is "structure-born" sound? If you are just talking about vibrations in a system, those can be picked up by a microphone, usually specific types made for vibration detectors (pretty much specialized accelerators) \$\endgroup\$ – Joren Vaes Jun 23 '18 at 10:57
  • \$\begingroup\$ "pick up" is musician talk. "Contact microphone" is a more general name for the same thing. \$\endgroup\$ – Solomon Slow Jun 23 '18 at 15:38
  • \$\begingroup\$ @JorenVaes - I think you really meant accelerometer which would be a sensor/measuring device. An accelerator would be something that causes acceleration such as punching the pedal in the car to the floor or pouring gasoline onto a trash fire. \$\endgroup\$ – Michael Karas Jun 23 '18 at 20:29
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A contact microphone is basically an accelerometer. It does not require any air for its operation.

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  • \$\begingroup\$ I noticed that there are some accelerometers than can be used for the job, but they suffer from poor bandwidth compared to a piezo contact microphone. Or they require really high Gs of acceleration. But I guess that accelerometers are possibly the best solution then. Thanks. \$\endgroup\$ – Karsten Becker Jun 24 '18 at 7:30
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if it is mounted on the same surface with the same vibrations, it in theory should measure nothing.

When sound waves propagate through solid material, it's not just the whole rigid object shaking back and forth: It's waves of strain.

Those strain waves will pass through a contact microphone that is attached to some small area of the surface. It will work better still if it can be wedged in between two different parts of some flexible structure:

Photo of piezo pickup wedged into the bridge of a string bass
Piezo pickup wedged into the bridge of a string bass (double bass)

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  • \$\begingroup\$ That is an interesting aspect, I will look into it to see if it is feasible, but I guess it requires some proper design with respect to tuning of the "clamp" to capture a wide range of frequencies without altering it too much. \$\endgroup\$ – Karsten Becker Jun 24 '18 at 12:18
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Pickups, like the ones used in guitars, are not strictly microphones. They work on a similar principle, but are coupled in some way to the object producing the vibration. I'm not sure exactly what kind of pickup you are thinking of, but I'm aware of two primary kinds:

  1. Magnetic Pickup
  2. Piezo Pickup

In the case of the first, the magnetic field inside the pickup will oscillate along with the (guitar) string's vibration; this causes an electric current which can be transmitted to a speaker. Magnetic fields can propagate through space without any air.

In the case of the second, the vibrations are carried through solid material (again, not air) into the magnet/coil pair which produces the electrical current. This will also work in a vacuum.

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