BRUEL & KJAER 2206 - Calibration; General; Calibration with Microphone Type 4148; Sound Measurements

3.4. CALIBRATION
3.4.1. General
The meter and microphone are calibrated together before they leave the factory to give
correct readings. The calibration is stable with time but can change due to the effects of
impact or adverse conditions . Frequent calibration should not be necessary. Certain meas-
urement codes of practice, however, specify how often equipment should be calibrated.
The 2206 may be calibrated by placing over the microphone an acoustical source
which produces a steady, known sound pressure level.
Either the Sound Level Calibrator Type 4230 or Pistonphone Type 4220 is recom-
mended. The 4230 generates 94 dB (± 0,25 dB) at a frequency of 1000Hz while the
4220 generates 124 dB (± 0,2 dB) at a frequency of 250Hz. Detailed descriptions of
these calibrators are to be found in their respective Instruction Manuals .
3.4.2. Calibration with Microphone Type 4148
The calibration procedure when the 2206 is used with the microphone with which it is
normally supplied (Type 41 48) is as follows :
1. Attach the microphone, extension rods or cables and adaptors by screwing them to-
gether finger tight. (See section 3.3.). These must be included in the calibration as
they all affect the sensitivity.
2. Turn the POWER SWITCH to "Batt." and check the battery voltage: Then set the
switch to "Fast" and the WEIGHTING NETWORK SELECTOR to either "C" or "Lin." .
3 . Set the RANGE SWITCH to either "90"dB if the Sound Level Calibrator Type 4230
is being used or "120"dB if the Pistonphone Type 4220 is being used. Allow about
25 seconds for the circuits to charge up.
4. Fit the half inch adaptor onto the acoustic calibrator then place the calibrator snugly
over the microphone . Switch on the calibrator and hold it steady on the micro-
phone .
5.
Adjust if necessary the screw of the SENSITIVITY ADJUSTMENT with a small screw-
driver to give a meter reading of either "+ 3,8" (equivalent to 93,8 dB) for the 4230
or to give a reading of the value on the calibration chart (corrected if necessary for
barometric pressure) for the 4220. (See also the relevant Calibrator Instruction Man -
ual).
3.5. SOUND MEASUREMENTS
3.5.1. General
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The accompanying booklet entitled Measuring Sound should be read through before pro-
ceeding with measurements as it contains much useful general information on the sub-
ject. One or two points should perhaps be emphasized. Ensure that the microphone has
the required dynamic range, frequency range and directional characteristics. Always use
a windshield for outdoor measurements and in a dusty environment.
Various nose cones are available for reducing wind noise as well as dehumidifiers. En- ·