Uses
- Simulated free- and diffuse-field calibration of microphones
- Verification of ½" and ¼" microphone setups and acoustic instruments conforming to IEC 60651 and ANSI S 1.4-1983
- Verification of instruments according to parts of IEC 61672
| Features
- Conforms to EN/IEC 60942 2003 Class I and ANSI S 1.40 – 1984
- Wide frequency range: 31.5 Hz to 16 kHz in octave steps, plus 12.5 kHz signal
- Calibration levels of 94 dB, 104 dB and 114 dB
- Free-field simulation for most ½" Brüel & Kjær microphones
- Inverse A-weighting
- Recurrent pulses for time-weighting and burst signal checks
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Working Principle
Type 4226 generates an accurate and stable SPL over a wide frequency range. The SPL obtained depends essentially on an internal reference microphone which is itself very stable with respect to time and temperature variation. The SPL produced is practically independent of atmospheric pressure changes. The calibrator gives an indication of when the SPL in the coupler is stable.
The response obtained Type 4226 from a microphone of any type, free-field or pressure, will always be its pressure response. However, the main interest for sound level meters is the free-field response. If the difference between the pressure response obtained with Type 4226 and the free-field response is known (as it is for most for Brüel & Kjær microphones,) the SPL in the coupler can be corrected as a function of frequency to obtain a flat response from an ideal free-field microphone. This SPL correction is automatically applied by the calibrator for different classes of Brüel & Kjær microphones.
In position "pressure", Type 4226 generates a constant sound pressure level in the coupler; then Type 4226’s correction for any microphone can be added to this value to achieve the free-field response.
An SPL of 94 dB ± 0.2 dB re 20 mPa at 1 kHz can be used for calibration purposes. Other calibration levels and frequencies may be used but with small increase in uncertainty (see Specifications).
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.
Note: At 31.5 Hz, the level in the coupler will reach 134...
For a full Description and Specifications, see Product Data
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