9/29/09 Performing a Sound Level Measurement 9-3
Editing the Microphone Parameters
The microphone to be used will either be a traditional
condenser microphone, which requires a polarization
voltage, or it will be an electret (prepolarized) microphone.
Further, if it is a free-field microphone and the measurement
is best performed using a random incidence microphone, the
user can select to implement a random incidence correction
to the measurement.
The procedure for selecting these parameters is described in
section ”Customizing Settings” on page 7-2, specifically the
sections ”Transducer Setting - (SSA, LOG, ISM)” on page 7-
8 and ”Random Incidence Microphone Correction -
(Available to all Instrument types)” on page 7-8.
Calibration
The System 824 automatically changes the frequency
weighting to C-Weighting during the calibration process.
Therefore, calibrators having frequencies which correspond
to the flat region of the C-weight curve (200 Hz - 1.25 kHz)
may be used. Larson Davis recommends the following
sound level calibrators:
• Larson Davis Model CAL200; 94/114 dB @ 1 kHz
• Larson Davis Model CAL250: 114 dB @ 250 Hz
The procedure for performing a calibration is described in
detail in section ”Turning On and Calibrating the System
824” on page 4-1.
If the Cal Level is not already set to the level provided by
the calibrator being used, this level must be changed by the
user. To do this, use the dkey to highlight Cal Level and
press the ckey. Use the horizontal and vertical arrow keys
to edit the level to match that of the calibrator and press the
ckey to enter the new value.
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