Tile scale readings are added to or snbtmeted from the dB range
level selected. For example, if the range selector is set at 80 dB, and a
meter reading of +8 is indicated, then the sound level measured is 88
dB, Similarly, if the meter needle is at -5 dB for the same range
selector setting, a noise level of 75 dB is indicated. In the latter case,
better readability will result if tile 70 dB range is selected, In this
case the I'teedle will point to +5 dB. again yielding Lhe nleasuren'tent
of 75 dB.
Most meter readings can and should Im taken with the slow
meter response because the nleter needle is more stable and easier to
read. The fast response is intended for measurement of short dura-
tion noises, such as moving vehicles or impulsive sound, where tile
noise is not present sufficiently long to obtain the maximun'_ reading
in the slow response mode. Keep in mind that for very short duration
impulse no[se even the fast i_sponse nlode lllay not be fast etlOtlgh to
indicate the truc peak noise level.
Effect of Operator's Presence
Any object or surface can act _n a reflector for sound. An
operator close to a sound level rglierol)hont_ ¢2allalso De a reflector,
causing areadirtgerror. When the souz'td to be rneasLired is directional,
the smmd level reading can be affected by the relative position of
meter and observer. The meter should not be held hetweell the noise
source and the observer because of sound reflections frolll tile body.
The meter should he held away from tim body or mounted on a tri-
pod with microphone pointed upward almost perpmldicuhr to noise
o
source (70 from path), keeping tile body out of the noise path
Effect of Backgromld Noise
If the sonnd level frorn a imrticular source is to be determined,
all surrounding sources of hoist! should, its nearly as possib/e, he
reduced or eliminated, When it is not possible to eliminate snrrmmd.
ing noise, tile curve shown in Figure 6 may be used to correct for the
presence of this noise.
Use With Windscreen
To prevent wind blowing across the microphone mid causing the
erroneous measuren_ent of sotlnd level, tlSe the Model WS-3 micro-
phone Windscreen with the sound level meter. The windscreen is
made of reticulated polyurethane foam for the reduction of ambient
wind effects, and can also protect tile microphone under dusty, oily
or humid conditions, Tile screen is simply pushed onto tile micro-
phone when needed. Acoustic attenuation effect of tile windscreen
on tile meter reading is small and is shown ill Figure 7,
8
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