Larson Davis System 824, Reference Manual

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11/3/00 D -15
Background: The all encompassing sound at a given location
caused by all sources of sound, but excluding 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 spec-
trum).
White: It is a random sound that contains equal energy at
each frequency. In this respect, it is similar to white light.
Noise Dose (D)
It is the percentage of time a person is exposed to noise that
is potentially damaging to hearing. Zero represents no expo-
sure and 100 or more represents complete exposure. It is cal-
culated 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.
where T is the Measurement Duration and T
i
is the Allowed
Exposure Time.
Standard: ANSI S12.19
Noise Exposure (See Sound Exposure)
OSHA Level (L
OSHA
) The Average Sound Level calculated in accordance with the
Occupational Safety and Health Administration Exchange
Rate and Threshold Level.
Preamplifier A part of the sound level meter that matches a particular
model of microphone to the meter. It must be chosen in con-
junction with a microphone and a cable that connects them.
Projected Noise Dose It is the Noise Dose expected if the current rate of noise
exposure continues for the full Criterion Duration period.
Single Event Noise Exposure
Level (SENEL, L
AX
)
The total sound energy over a specific period. It is a special
form of the Sound Exposure Level where the time period is
D 100
T
T
i
----
100T
T
c
------------10
L
i
L
c
–
( )
Q
⁄
= =