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A-Weighted Sound Level
The sound pressure level in decibels as
measured on a sound level meter using the A-weighting network. A-weighted
sound levels are designated dB(A) or dBA.
Day-Night Average Sound Level (Ldn)
The 24-hour energy average of the A-weighted
sound pressure level, with the levels during the period 10:00 p.m. to 7:00
a.m. the following day increased by 10 dBA before averaging.
Decibel (dB)
A unit for measuring the volume of a sound,
equal to 20 times (the logarithm to the base 10 of the ratio of the pressure
of the sound measured to the reference pressure, which is 20 micropascals
(20 micronewtons per square meter).
Equivalent A-Weighted Sound Level (Leq)
The constant sound level that in a given
situation and time period, conveys the same sound energy as the actual
time-varying A-weighted sound.
Impulsive Sound
Sound of short duration, usually less
than one second, with an abrupt onset and rapid decay. Examples of
sources of impulsive sound include explosions, drop forge impacts, and
the discharge of firearms.
Noise
Any sound which annoys or disturbs humans
or which causes or tends to cause an adverse psychological or physiological
effect on humans.
Pure Tone
Any sound which can be distinctly heard
as a single pitch or a set of single pitches.
RMS Sound Pressure
The square root of the time averaged square
of the sound pressure, denoted P(rms)
Sound
An oscillation in pressure, particle displacement,
particle velocity or other physical parameter, in a medium with internal
forces that causes compression and rarefaction of that medium. The description
of sound may include any characteristic of such sound, including duration,
intensity and frequency.
Sound Level
The weighted sound pressure level obtained
by the use of a sound level meter and frequency weighting network, such
as A or C, as specified in the American National Standards Institute specifications
for sound level meters (ANSI S1.4), or the latest approved revision thereof.
Sound Level Meter
An instrument which includes a microphone,
amplifier, RMS detector, integrator or time averaging device, output meter,
and weighting networks used to measure sound pressure levels.
Sound Pressure
The instantaneous difference between the
actual pressure and the average or barometric pressure of a given point
in space, as produced by sound energy.
Sound Pressure Level
20 times the logarithm to the base 10
of the ratio of the RMS sound pressure to the reference pressure of 20
micropascals (20x10µN/m). The sound pressure level is denoted Lp,
or SPL and is expressed in decibels.
Vibration
An oscillatory motion of solid bodies
of deterministic or random nature described by displacement, velocity,
or acceleration with respect to a given reference point.
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