Calibrating A Noise Dose Meter - BRUEL & KJAER 4226 User Manual

3.9

Calibrating a Noise Dose Meter

Type 4226 may be used to calibrate a noise dose meter. This is because it can generate an
acoustic tone in its coupler with a well-defined sound level, frequency and duration.
The frequency is chosen in the normal way via the
frequency of 1 kHz will suffice in most cases. A well-defined sound level is available whenever the
switch is set to Calibration. The duration of the tone after pressing the
Function
is exactly 30 seconds.
The general procedure is to place the microphone of the noise dose meter in the coupler and note
the change in measured dose for the 30-second period (after pressing the
3.5 shows what changes to expect for properly adjusted IEC and ANSI noise dose meters which
record a 100% noise dose for a sound level of 90 dB lasting 8 hours.
✐
If the noise dose meter has an unlisted microphone (see section 3.5), the Sound Field
Please note:
switch must be set to Pressure.
Table 3.5
Expected changes in
measured noise dose
for IEC and ANSI noise
dose meters which
record a 100% noise
dose for 90 dB lasting
8 hours. Expected
changes for tones of
three different levels
are shown
3.9.1 Calibration Using Tones Lasting More Than 30 Seconds
The procedure here is similar to that outlined in section 3.9.1 except that the timer on Type 4226
is not used. The noise dose meter must be set to measure noise dose in the normal way and you
should note changes in measured noise dose brought about by a known tone level in the coupler
acting over a known period. The A-weighting network may also be checked by using the 94 Inv.
A setting on Type 4226.
Table 3.6 and Table 3.7 show the expected results for a 10-minute period for all four Sound Level
settings of Type 4226's for tones of all frequencies. It is useful to note that, all things being equal,
the measured noise dose is proportional to the measurement time, that is, the results shown in
Table 3.6 and Table 3.7 are 20 times greater than the corresponding results shown in Table 3.5.
SPL (dB)
94
104
114
buttons, normally the default
Frequency Step
IEC
0.26%
2.62%
26.2%
CHAPTER 3
23
Operation
button once
Timer
button). Table
Timer
ANSI
0.18%
0.73%
2.90%