Hi there,
I'm going to perform a behavioural experiment in a closed plexiglass chamber, linked to a ventilation system through a hole (let's think about it as a fume hood). In this experimental design I would like to record ultrasound vocalization (from 18kHZ) of an adult mouse, but I cannot put the microphone for detection (condenser microphone, 2 - 200 kHZ) inside the box.
If I keep it outside the plexiglass chamber, how much the signal of USVs will cross the plexiglass? Can I detect them without so much lost? Can the ventilation system affect the signal?
Thank you!
The difference in acoustic impedance between air (~400 Rayls) and plexiglass (2.77 MRayls) will lead to very high reflection coefficients at the air/plexiglass and plexiglass/air interfaces, and therefore very low transmission coefficient, unless the plexiglass layer is extremely thin or the thickness is very close to 1/2 the wavelength in plexiglass (at 18 kHz, it is about 6.53cm, assuming 2350 m/s). For a 60 µm thick plexiglass layer the transmission coefficient would be around 0.1, and getting higher as thickness decreases. But that would not be very practical. If you target the 1/2 wavelength plexiglass thickness, note then that the transmission coefficient is going to be very narrow band (a couple of Hz), i.e. if you design the wall for 18 kHz, the transmission coefficient is going to drop very quickly as the frequency deviates from 18 kHz.
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