For example, if the background noise is 45dB and the sound of interest
measures 51dB, the difference between measurement and background
noise is 6dB. From Figure 3, for a 6dB difference, 1.3dB should be
subtracted from the measurement. The correct measurement is therefore
51dB- 1.3dB = 49.7dB.
4.3 Wind Screen Effects:
To prevent measurement errors caused by wind blowing across the micro
phone, the use of a windscreen is recommended. The wind screen will
reduce wind effects and will also help protect the microphone under dusty,
oily, or humid conditions. Acoustic attenuation effects of the windscreen
(WS-7) are shown in Figure 4.
4.4 Data Recording:
The model 1200 has a DC output that is linearly related to the decibel
reading on the LCD display by 16.7mV/dB (1V/60dB).
This output, capable of driving up to 100 feet of shielded or twisted pair
cable, is intended for use with a chart recorder or data acquisition device
that has a high input impedance. The output impedance is 1000 ohms.
Recorder input impedance may cause loading of this output, which should
be taken into account. Multiplication factors for the above numbers are
given below for various recorder input impedances.
INPUT IMPEDANCE OF
RECORDER:
MULTIPLY DC VOLTAGE
BY:
10 KOHM
20 KOHM
50 KOHM
100 KOHM
1.100
1.050
1.020
1.010
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