Bruel and Kjaer 4220 Sound Level Calibrator

Bruel and Kjaer 4220 Sound Level Calibrator

Rent me for $100 a month

   Designed for accurate everyday calibration of sound level meters using .5 in. and 1 inch microphones. Pocket sized sound source designed for for accurate, everyday field calibration of sound level meters using .5 in. and 1 inch microphones.

Features

• Sound pressure level 124dB
• Calibration accuracy ± 0.2dB
• Frequency 250Hz ± 1%
• Distortion < 3% at 250 Hz
• Power Source: Internal. 9 Volt battery

   The 4220 is designed for the calibration of 1'' and 1/2'' diameter microphones. An adaptor is placed over the opening for use with 1/2'' microphones and is removed when 1'' microphones are to be calibrated. The sound pressure level produced by the 4220 is 124 dB . However, when calibrating a microphone which is to be used for free field measurements, a small correction is necessary to compensate for the difference between free field response at 0° incidence and the pressure response. The correction is -0,4 dB for 1'' free field microphones and -0,2 dB for 1/2" free field microphones. This makes the effective calibration levels 123.6 dB and 123,8 dB respectively. No correction is required when calibrating pressure response microphones.
   Adaptors are available so that the B & K 1/4" and 1/8" microphones can be calibrated using the 4220. For 1/4" microphones, the adaptor DB 0310 is required. For 1/8" microphones both adaptors DB 0310 and DB 0352 are required. In each case the extra adaptors fit inside the 1/2" microphone adaptor supplied (DB 0311).

Calibration Procedure

1. Select and fit the requisite adaptor to the 4220
2. Place the 4220 snugly over the microphone
3. Press the button on the 4220. A hold circuit maintains the signal for up to one minute (with a new battery) after the push button is released.
4. Adjust the sensitivity of measuring equipment to read the appropriate value (see Table)

   Table: Indication required from measuring equipment for various microphone types

Pressure Response	124 dB
Free Field Response	1 inch microphones: 123,6 dB 1/2 inch microphones: 123,8 dB

Replacement of Battery

   If the calibration signal lasts only a few seconds after the push-button on the 4220 has been released the the battery needs replacing.  The battery is a 9 V type IEC 6F 22 or NEDA 1604.

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