The Sound Calibrator Nor1257 is a small, battery operated sound source for the calibration and check of sound measuring instruments. The specifications conform to the requirements in the French standard NF S 31-010, Annex B (1996).
The combination of three different levels and six frequencies in octave steps in the range from 125 Hz to 4 kHz allows both level linearity and frequency linearity to be verified. In addition, the Sound calibrator measures the environmental conditions: air pressure, temperature, and humidity.
The microphone of the sound level meter shall be placed in the acoustic coupler of the calibrator before the calibrator is switched ON. After startup, the calibrator will produce a regulated sinusoidal sound pressure signal at 1 kHz with a sound pressure level
of 94,0 dB. The sound is generated by a small loudspeaker integrated into the acoustic coupler.
The level is measured with an internal reference microphone and is automatically adjusted until the level is correct. This is indicated by the LED on the front turning from red
to green. The feedback ensures that the sound level is nearly independent of the acoustic load volume of the microphone.
By pressing the “dB” button, the sound pressure level may be set to 74 dB and 44 dB respectively. Note that the calibrator uses the level settings at 94 dB and attenuate the sound 20 dB and 50 dB, respectively.
Therefore the level has to be stable as indicated by the green LED at 94 dB before the other levels are selected. Otherwise an error will be displayed.
Other frequencies may be obtained by pressing the button “Hz”. The frequency is changed in the following sequence: 1 kHz – 2 kHz – 4 kHz – 125 Hz – 250 Hz – 500 Hz – 1 kHz …. Note that after a change in frequency, the level is set to a A-weighted level of 94 dB where the regulation based on feedback is performed.
The calibrator is adjusted to levels suitable for ½” freefeld microphones, microphone type WS2F as specifed by IEC 61094-4. See the technical information for other types of microphones.
Due to the principle of operation, the calibration level is virtually independent of ambient conditions like temperature, atmospheric pressure, and humidity within the specifed range of operation. The calibrator complies with IEC 60942 class 1 for the specified 94 dB levels.
The calibrator has been designed to serve oneinch and smaller microphones and sound level meters equipped with such microphones. One-inch microphones ft directly in the calibrator coupler, while
half-inch and smaller microphones are served by application of a suitable adaptor. Adaptor for half-inch
microphones is included, while adaptors for other
microphone sizes must be ordered separately. Note
that the levels are set to ft typical ½” free-feld microphones, microphone type WS2F. Other microphones
needs corrections to be applied.