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Figure 9
. Placement of Microphone When Used as a Personal Monitor.
5. GENERAL SOUND MEASUREMENT PRACTICES
Before taking measurements with the Q-300 there is a series of quick checks that should be performed. After switching
the unit ON, check for the LOBAT indicator in the display. Replace the battery if needed.
Although the Q-300 will maintain accurate calibration over a long period of time, the calibration should be checked and
the calibration routine run, if necessary, before each use.
When performing integrating measurements, press the RUN/PAUSE key, making sure " RUN " is indicated in the
display. It is always a good idea to document all measurement conditions and meter settings for possible future needs. If the
data is printed, the settings will all appear on the printout.
5.1 Microphone Positioning
The dosimeter measures sound most accurately without the presence of sound reflecting or absorbing objects. Any
near-by object or surface (including the operator) will act as a reflector or absorber of sound. To minimize these errors, use the
dosimeter as follows:
When taking Personal Noise Dosimeter Measurements:
Connect the Microphone to the shirt at the shoulder. (See Figure 9) Keep it high on the shoulder and away
from the neck if possible.
If the noise seems to be coming from one location, place the microphone near the ear facing that location.
Install a Windscreen on the microphone. It holds the microphone in an upright position and keeps the microphone from
brushing against clothing, which can produce high noise levels into the microphone.
When taking Stand-Alone measurements:
Mount the dosimeter to the tripod mount (located on the belt clip) with the microphone upward forming
approximately a 70 degree angle with the noise source.
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5.2 Accuracy of Readings
For maximum accuracy, it is important to use the dosimeter correctly and to understand its limitations. It will correctly
integrate all sound levels within the range of the instrument.
A few items related to accuracy are as follows:
There is a tendency to overestimate the accuracy of digital readings. The values (such as Leq) are computed to a
precision of 0.1 dB. However, the absolute accuracy of the reading is not 0.1 dB, but is accurate to the stated overall accuracy
of the instrument.
The 0.1 dB resolution is useful in determining the minimum sample time required to get an accurate short term
measurement.
If, for example, the Leq is increasing 0.3 dB every second, then a longer sample time is required.
If the Leq is remaining stable from second to second within a few tenths of a dB, then the sample time is long
enough.
5.3 Microphone Windscreen
It is recommended that a windscreen be used at all times. The Q-300 uses the WS-5 Windscreen. Using a windscreen will
improve the accuracy by minimizing the effect of the following:
Wind blowing across the microphone can produce higher than normal sound level readings. The windscreen blocks
wind from direct contact with the microphone, producing less unwanted noise.
Clothing brushing against the microphone can produce higher than normal sound level readings. The windscreen helps
position the microphone so that clothing cannot brush against it as easily.
Dirt entering the microphone, in time, can damage the microphone, possibly changing the microphone's frequency
characteristics. The windscreen catches and collects this dirt before it enters the microphone.
Simply insert the microphone into the windscreen and gently pull it over the Velcro strip.
5.4 Background Noise
Background noise can cause considerable error in measurement when its level is close to that of the noise source of
interest. When it is not possible to eliminate or reduce the background noise, use the curve shown in Figure 10 to correct for
the effect of the background noise on the measurement.