SMX-US Microphone
Copyright © 2009-2011
Song Meter SM2BAT
2
SMX-US Microphone
The SMX-US is an ultrasonic microphone designed for terrestrial monitoring
applications, specifically for recording the echolocation calls of bats.
Notes on Weatherproofing
The transducer inside the SMX-US microphone
can be permanently
damaged
if it is exposed to water in the event that the weatherproofing
fails.
To protect the transducer, there are trade-offs between ultrasonic sensitivity
and weatherproofing.
The SMX-US features several layers of protection. First, a porous
membrane transparent to ultrasound prevents unpressurized liquid water
from entering the microphone. However, the membrane is rated to only 0.07
lbs/in
2
or 5g/cm
2
. This is easily exceeded by wind-blown rain. The foam
windscreen provides a critical second layer of protection to absorb the
impact of wind-blown rain so that only unpressurized water reaches the
membrane effectively protecting the transducer. When dry, the foam
windscreen is almost transparent to ultrasound with a loss of only 2dB.
However, the loss increases with frequency when wet, and will effectively
block ultrasound if it then freezes.
The membrane is also fragile. The foam windscreen adds a layer of
protection against insects, rodents and birds who will tend to nibble on the
windscreen instead of the membrane.
We strongly recommend operating the SMX-US with the windscreen, and
replacing the windscreen if it becomes fully or partially eaten.
We also recommend positioning the microphones so that they point parallel
to the ground, or even slightly downward. In this configuration, even if the
windscreen is absent and water penetrates the membrane, the water should
not collect in sensitive areas inside the microphone and there is a good
chance that the transducer will survive. If you suspect that water may have
entered the microphone, you should avoid handling it until it has
completely dried out. Otherwise water could change position and come in
contact with the transducer resulting in damage.
If you are deploying the SM2 in field conditions expected to remain wet or
frozen, you may want to operate the SMX-US microphone without its foam
