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
- Select and fit the requisite adaptor to the 4220
- Place the 4220 snugly over the microphone
- 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.
- 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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