BRUEL & KJAER 4226 User Manual page 11

The construction of the calibrator also enables you to connect an external generator (for example,
for frequency sweeps) or to pick up an electrical calibration signal (for example, for filter checks).
Fig.1.3
Simplified cross-section
of the acoustic coupler
1.2.1 Calibrating the Sensitivity
An SPL of 94 dB ±0.2 dB re 20 μPa at 1 kHz can be used for calibration purposes. You can use
other calibration levels and frequencies with slightly reduced accuracy. See the specifications.
1.2.2 Checking the Frequency Response
Type 4226 delivers a very stable tone with a frequency varying from 31.5 Hz to 16 kHz in octave
steps, with an extra tone at 12.5 kHz. The 12.5 kHz tone is used for checking the highest frequency
specified for type 1 sound level meters. The actual frequency of the tone corresponds to those
frequencies recommended in ISO 266.
1.2.3 Checking A-weighting Networks
A 94 dB inverse A-weighted SPL can be applied in the acoustic coupler of Type 4226. This means
that an SPL of 94 dB, plus the corrections due to the microphone type and the sound field type,
plus the inverse A-weighting correction is produced in the coupler. All the corrections are, of
course, frequency-dependent, so to check an A-weighted measuring instrument means making
sure that it reads 94 dB within the tolerances.
✐
At 31.5 Hz, the level in the coupler will reach 134 dB.
Please note:
1.2.4 Checking Input Attenuators
Using the three calibrated levels of 94, 104 and 114 dB at all frequencies, the proper function of
the input attenuators of an instrument can be tested.
Low-frequency Transducer
High-frequency Transducer
Reference Microphone
Electronic
Circuitry
½-inch
Adapter
Microphone
to calibrate
880608/11
CHAPTER 1
3
Introduction