4
$\begingroup$

I would like to record extremely low sound-level (at ~200-300Hz), produced by an insect which is located at the end of a plastic tube, with a very-sensitive low-noise shotgun pressure microphone (this is a constraint). Shotgun microphones are highly directional due to an interference system between sensors along their body.

My first intuition was that it is not the best idea to put the tip of the microphone inside the plastic tube because it would isolate the mic's top sensor from those in the mic's body. However, this would 1) avoid adding an insect net (which would attenuate the already too quiet sounds) to close the tube as the mic tip would do it instead (sealing is required as I work wirh an invasive pest) and 2) get the mic closer to the insect.

From a theoretical point's of view (i.e. without testing it), would the shotgun microphone work properly enough if its tip is inside the plastic tube (case B below)? Or do you think that leaving a small space between the tube and the microphone tip would be better (cas A below)? My only criteria is to get a decent signal-to-noise ratio to record these very quiet sounds (I don't care about any sound-amplitude distortion).

enter image description here

A: tip of the mic at a short distance to the plastic tube + net on the tube

B: tip of the mic inside the plastic tube which seals the plastic tube

Improve this question
$\endgroup$

1 Answer 1

Reset to default
2
$\begingroup$

Considering the large difference between the size of the insect and the wavelength of interest, sound radiation must be very weak, indeed. Is that a species that signals by tremulation? Specific techniques have been developed for that.

I would not use a shotgun microphone here. There is no obvious gain in sensitivity with respect to a more classical cardioid or omnidirectional microphone. At 250 Hz the directivity pattern is not sharp either. Moreover, in configuration A, I suspect very little sound would reach the sensors along the body. So that would not make much difference with configuration B. If the issue is background noise, if you have the possibility to place the insect in a tube, perhaps you can carry the insect to a quiet place for the needs of the recording.

About configuration A, I am sure you can find a net that is acoustically transparent in the frequency range of interest.

However, I think you would be better off with a classical microphone in config. B. A potential issue with config. B is the transmission of mechanical vibrations to the body of the microphone. This can be avoided by adapting the inner diameter of the tube so that it is slightly larger than the diameter of the microphone or by mechanically decoupling the termination of the tube from the tube itself. Again, if your research is about tremulation, measuring substrate vibrations would be a better option.

Improve this answer
$\endgroup$
1
  • 1
    $\begingroup$ If there is a direct mechanical coupling between the tube and the microphone body, it means that both airborne sound and mechanlcal vibrations are likely to generate a response from the microphone. These two will a priori travel at different speeds. I suspect you will not get any benefit from it. Hopefully one path will be negligible with respect to the other. Moreover, picking up sound by direct mechanical coupling would be an unconventional way of using a microphone. $\endgroup$
    – Guillaume Dutilleux
    Commented Sep 5, 2022 at 11:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.