skcinc.com
Form 37177 Rev 200910
Page 6
The SoundCHEK Essential will register an overload if the noise level exceeds the linear operating range
of the range selected by 0.5 dB, so it is advisable to determine if an overload will occur on the selected
range before measuring. In such cases, you will need to select a higher range to accommodate the higher
peak levels.
If the noise levels are 0.1 dB too low for the range selected, then the meter will display an under range
condition. Under these circumstances, you will need to select a lower range. For detailed information, see
Measurement Setup, Weightings & Range
.
If measuring low level noise, be aware of the inherent noise levels caused by a combination of thermal
and electrical noise from both the microphone and the sound level meter. Measuring data that lies within
10 dB of the lowest quoted level on the lowest measuring range may be influenced by the self-noise of
the system.
Reflections
The sound level meter operator and the sound level meter itself can interfere with the measurements
being made, reflecting the noise signal. The instrument case for all SKC sound level meters has been
designed to minimize reflections while also being of rugged construction.
To
minimize reflections from the operator, hold the sound level meter at arm’s length or mount the sound
meter on a suitable tripod.
Time Weighting
The time weighting is a time constant that modifies the response of the instrument to fluctuating noise
levels. Without time weighting the meter display would fluctuate following the measured noise level and
would be unreadable, the selected time weighting therefore softens these fluctuations over the time
periods described below and in doing so the meter has a more readable display.
All SoundCHEK Essential sound level meters use digital time weighting filters for higher accuracy. The
following standardized time weightings are available:
•
Slow Weighting
shows a slow rise in the Sound Pressure Level even for a sharp rise in the noise
level, likewise a rapid reduction in noise will be shown as a slow decrease in Sound Pressure
Level. The rise and fall times applied for Slow Weighting are 1 second.
•
Fast Weighting
is the most commonly used time weighting. It follows the noise level closer than
slow weighting by displaying a fast rise and fall in the Sound Pressure Level. The rise and fall
times applied for Fast Weighting are 125 milliseconds
.
•
Impulse Weighting
allows your meter to show rapid rises in the noise level but has a very slow
decay. The rise and fall times for Impulse Weighting are 35 milliseconds and 1.5 seconds,
respectively.
Frequency Weighting Filters
Frequency Weightings are where the Sound Pressure Level is modified by use of filtering. All
SoundCHEK Essential sound level meters use digital frequency weighting filters for higher accuracy. The
following standardized frequency weightings are available; the frequency weighting curve for each one is
shown in the graph below.