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Environmental Monitoring (Environmental Monitoring)
fiori, paoletti - 15:47 Thursday 15 January 2009 (21732) Print this report
test of Infra-sound microphone
We tested the new microphone B&K mod. 4193 just bought by EGO. From specs. its low frequency limit is around 0.1Hz (+-2dB). to be compared with the 4Hz lower limit of our standard microphones (B&K mod 4190). Upper limit is as well 20kHz. We did a cross calibration of the two by placeing both close and parallel. The measurement was taken inside the DAQ room.
Figure 1 shows how the new one performs with respect to the standard one. See that the air pressure noise at 100mHz is 30 times the noise at few Hz.
Figure 2 shows a tech. detail measurement. That is we measured and compared the microphone response with and without using the LowFrequency Adaptor UC-0211 which comes together with the mic. preamplifier.

Just got from Wiki-pedia:
" Infrasound, is sound with a frequency too low to be heard by the human ear. The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath the lowest limits of human hearing (20 hertz) down to 0.001 hertz. This frequency range is utilized by seismographs for monitoring earthquakes. Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation."
... we now have a better window on these!
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fiori, paoletti - 10:39 Monday 19 January 2009 (21753) Print this report
As Federico noticed, our measurement is likely limited by the Nexus conditioning electronics used to amplify the mic signal: the Nexus applies a high-pass filter with 0.1 Hz cut-off which suppress signal by -2dB at 0.1Hz and by -20dB at 0.01Hz. We should investigate the possibility to lower the cut-off of this filter (seems not obvious according to Nexus specs) or build a dedicated electronics (possible, says Federico).

For the moment (until we find a better location, or until the sensor is not needed for other measurements) we left (since Jan 14) the infra-microphone recording with the name "Em_AC_EE_fanC" inside the DAQ room. The low freq. signal (<1Hz) should not really depend on the location of the probe inside the CB.
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