MK:427 Environmental Noise Microphone
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Example
For the range of 34 to 104dB
dB = (10 x I ) – 10, where I is the current output in mA.
The current output for a known dB level is therefore
I = (dB +10) /10
6.
Carefully remove the acoustic calibrator
7.
Remove the microphone grill
8.
Re-attach the electrostatic actuator and cable
9.
Activate the electrostatic actuator system by applying a voltage of b5v and +12 to the
Yellow wire. The Green wire should be connected to 0V of this voltage source.
10.
Record the output current across the loop to obtain the actuator output level
Please note that the level produced by the electrostatic actuator is dependent upon the position
of the actuator drive plate above the microphone grill and will vary slightly depending upon how
tightly it has been screwed down.
Very small changes in position can produce significant differences in the level produced by the
actuator system.
The actual level produced by the electrostatic calibration system is not important, only that it
produces the same reference level each time.
Example
The level produced by the actuator is calculated from dB = (10 x I) – 10 for an instrument with
the range of 34-104dB, i.e. an output current of 8.75mA corresponds to an actuator level of 77.5
dB(A)
Barometric pressure and outside temperature will have small effects on the actuator level and so
small variations up to 0.5dB are not uncommon between day and night conditions or between low
and high pressure days.