Some Fundamentals of Sound
Audible sound is caused by barometric fluctuations in the freqency
range from 16 to 16,000 cycles per second (16 Hz... 16kHz). These
fluctuations are measured in the physical unit Pascal (Pa). The human
ear can recognize sound pressures in the range from about 0.00002 Pa
(threshold of hearing) to 100 Pa (threshold of pain). Due to this
extremely wide range, a logarithmic measure – the decibel (dB) – is
used for clarity. The dB value for the audibility threshold is 0 dB and for
the pain threshold 140 dB.
The sensitivity of the human ear is frequency-dependent. Our ear is
less sensitive to very low and very high frequencies than to middle
frequencies (1 kHz). This characteristic of the human ear is simulated
by the so-called A-filter in sound level meters. Many acoustic
measurements such as traffic noise measurements are performed with
A-weighted levels. The measured values are usually labeled with the
suffix (A), e.g. 65 dB (A).
For measuring annoyance or even damage to hearing, a so-called
average level is important in addition to the maximum sound level. This
average level or “equivalent continuous sound pressure level” Leq is
used for evaluating heavily fluctuating levels.
When evaluating with Leq it must be considered that it does not take
into account properties of sound that are perceived differently by
different people. Thus, aircraft noise is often perceived to be more
annoying than railroad noise and truck noise more annoying than
motorcycle noise.
The reason for this is the different frequency distribution of sounds.
When calculating levels, these properties can be taken into account by
means of standard additions and reductions without the need to
calculate frequency spectra.
Due to the logarithmic graduation of the dB-scale, two sound sources of
the same loudness cause together exactly 3 dB more noise than each
of them alone. The apparently paradoxical statement that
0 dB + 0 dB = 3 dB becomes understandable when bearing in mind that
0 dB does not correspond to 0 Pa, but to the human threshold of
hearing.
A level shift of 3dB can just about be perceived by the human ear; a
level reduction of 10 dB is necessary in order to halve the perceived
loudness.
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Equivalent Continuous Sound Level
This operating mode displays the equivalent continuous sound level
(Leq) over a given measurement period. The measurement is started
and stopped with [SET], as for the maximum sound level mode. The
measurement range must be selected before the measurement is
started. During the measurement period the digital display shows the
short-time Leq over 1 s. After finishing the measurement, the Leq for the
measurement period is shown; if an overload occurred during the
measurement, this is indicated by the arrow symbol.
Tip: In order to find the most suitable measurement range
for Lpmax or Leq, a preliminary measurement should be
made with Auto-range in the Lpoperating mode.
Technical Data
Accuracy Type 2 according to IEC 60651 / 60804
Measurement range 30 ... 130 dB (A)
Operating modes - Sound level Lp
- Maximum sound level Lpmax
- Equivalent continuous sound level Leq
Level ranges 30 ... 90 dB
50 ... 110 dB
70 ... 130 dB
Autorange in Lpmode
Frequency weighting A
Time weighting Fast
Display - Measured value with 3.5 digits
- Bar graph in 5 dB steps
- under-range andover-range indicator
- Operating mode, measurement range
- Battery status
Microphone ¼” electret
Calibration Automatic to 93.5 ... 94.5 dB
(use 93,9 dB with 511E calibrator)
Batteries 2 x R6, alkaline, NiMh, NiCd
Operating time 100 h (alkaline batteries)
Dimensions 170 mm x 62 mm x 30 mm
Weight 160 g (with batteries)
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