User`s manual

8.4 THE SOUND LEVEL METER
Selecting Pressure as measured parameter gives your Multi-meter the functionality
of a Sound Level Meter. Three units are available: dBSPL, dBA and dBC. dBSPL is a
direct reading of the sound level, relative to the reference pressure of 20uPa.
Remember that CLIO needs to know your microphone sensitivity to carry out this
measurement correctly (see 5.4.2). dBA and dBC are frequency weighted
measurements and are usually requested to assess, for example, environmental
noise or any human related annoyance. In these two cases the program post
processes the measurement, applying the appropriate frequency filter as described
in IEC-651 norms.
8.4.1 CAPTURING THE MICROPHONE SENSITIVITY
When measuring pressure, it is possible to calibrate your measuring chain if you
have a pressure reference available like an acoustic calibrator. It is possible to
calibrate both channels.
In this situation, pressing the button will prompt the instrument to capture a
pressure reading as reference for the reading channel; it expects a reference
pressure level at its input, as furnished by the vast majority of acoustic calibrators;
it is possible to input its value cliking on the drop down menu; the default value is
94dB. As a result of this procedure the program will calculate the sensitivity, in
mV/Pa, of the microphone front end, and store it in the CLIO settings.
Figure 8.6
If you press the button's drop down you will see a reference to the actual
Microphone sensitivity. In this case, differently from the case of Voltage
measurements, the default measurement is 17 mV/Pa, which is a rough average of
Audiomatica's microphones MIC-01 and MIC-02 sensitivity. Let's see how to capture
the channel A microphone sensitivity. In Figure 8.7 you see a Bruel & Kjaer 4231
acoustic calibrator fitted to a MIC-02 microphone.
Figure 8.7
8 MULTI-METER 95