Larson Davis SoundAdvisor 831C Reference Manual page 213

Noise
Noise Dose (D)
Noise Exposure
OSHA Level
(LOSHA)
Preamplifier
SoundAdvisor Model 831C
Geometric Near Field: The distance from a source of sound is less than the
largest dimension of the sound source. In the near field, effect of source geometry
is significant. Sound sources often have a variety of specific sources within them,
such as exhaust and intake noise. When in the near field, the sound of a weaker,
but close, source can be louder than that of a more distant, but stronger, source.
Therefore measurements made here can be used to separate the various sources
of sound, but are not useful in predicting the sound levels and sound spectrum
far from the source.
Typically it is unwanted sound. This word adds the response of humans to the
physical phenomenon of sound. The descriptor should be used only when
negative effects on people are known to occur. Unfortunately, this word is used
also to describe sounds with no tonal content (random):
Ambient: The all encompassing sound at a given location caused by all sources
of sound. It is generally random, but need not be.
Background: The all encompassing sound at a given location caused by all
sources of sound, but the source to be measured. It is essentially the sound that
interferes with a measurement.
Pink: It is a random sound that maintains constant energy per octave. Pink light
is similar to pink noise in that it has a higher level at the lower frequencies (red
end of the spectrum).
White: It is a random sound that contains equal energy at each frequency. In this
respect, it is similar to white light.
It is the percentage of time a person is exposed to noise that is potentially
damaging to hearing. Zero represents no exposure and 100 or more represents
complete exposure. It is calculated by dividing the actual time of exposure by the
allowed time of exposure. The allowed time of exposure is determined by the
Criterion Duration and by the sound level (the higher the level, the shorter the
allowed time). The sound levels must be measured with A-frequency weighting
and slow exponential time weighting. See "Projected Noise Dose" on page C-12.
where T is Measurement Duration, T
q is exchange rate factor; see "Exchange Rate (Q), Exchange Rate Factor (q),
Exposure Factor (k)" on page C-6.
Standard: ANSI S12.19
"Sound Exposure (SE)" on page C-12.
The Average Sound Level calculated in accordance with the Occupational Safety
and Health Administration Exchange Rate and Threshold Level.
A part of the sound level meter that matches a particular model of microphone to
the meter. It must be chosen in conjunction with a microphone and a cable that
connects them.
  q 
L i L c –
100T
----------- - 10
D =
T c
is Criteria Time, L
c
is TWA, L is Criteria Level,
i c
C-11