Larson Davis 831, User Manual

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Model 831 Manual Acoustic Calibration 8-5
Acoustic Calibration
When using a 426A12 Outdoor
Microphone and Power Supply or a
Model 2100 Outdoor Preamplifier, a
calibration check can be performed
remotely using an electrostatic
actuator (E.A.) as described in "E.A.
Check" on page 8-18. This is the most commonly used calibration method, and the
one required by most national and international standards
prior to performing a measurement. A sound level calibrator
is used to apply an acoustical signal of a known amplitude
and frequency to the microphone. From the voltage level
measured by the meter the sensitivity can be determined. In
this technique one is obviously assuming that the calibrator
is functioning correctly; any variation in level from that
expected will result in an improper calibration and an
erroneous value of sensitivity. For this reason, the user is
advised to compare the newly determined sensitivity with
the previous sensitivity to ensure that significant variations
have not occurred.
Frequency Weighting
The Model 831 automatically switches to C frequency
weighting and Fast detector response for calibration. This
permits 250 Hz and 1000 Hz calibrators to be used. The Fast
detector response reduces the stabilization time required
before calibration. If the OBA is enabled and the OBA range
is set to Low, an OBA overload will occur due to the
amplitude of the calibrator output signal. Therefore, the
OBA range is automatically switched to high for the
calibration.
After calibration, the Model 831 returns to the original
frequency and time weighting set by the user. If the OBA is
enabled, the OBA range is also restored to that set by the
user.
Calibrator
The calibrator section of the Calibrate tabs, shown in
FIGURE 8-2, includes an area to enter information about a
calibrator and a list of calibrators. The user may select a
calibrator from the list or enter new information about a
calibrator.
Recommended Calibrator
Larson Davis recommends the following calibrator:
If using a 1/4” microphone, the
adaptor ADP024 is required. • Larson Davis Model CAL200: 94/114 dB @ 1 kHz