Geoscience Reference
In-Depth Information
Attenuate— To reduce the amplitude of sound pressure (noise).
Attenuation— See real ear attenuation at threshold (REAT), real-world attentuation
Audible range —The frequency range over which normal ears hear: approximately 20 Hz
through 20,000 Hz.
Audiogram— A chart, graph, or table resulting from an audiometric test showing an indi-
vidual's hearing threshold levels as a function of frequency.
Audiologist —A professional, specializing in the study and rehabilitation of hearing, who is
certified by the American Speech-Language-Hearing Association or licensed by a state
board of examiners.
Background noise —Noise coming from sources other than the particular noise sources being
monitored.
Baseline audiogram —A valid audiogram against which subsequent audiograms are com-
pared to determine if hearing thresholds have changed. The baseline audiogram is pre-
ceded by a quiet period so as to obtain the best estimate of the person's hearing at that time.
Continuous noise —Noise of a constant level as measured over at least one second using the
“slow” setting on a sound level meter. Note that a noise which is intermittent (e.g., on for
over a second and then off for a period) would be both variable and continuous.
Controls, administrative —Efforts, usually by management, to limit workers' noise exposure
by modifying workers' schedules or locations, or by modifying the operating schedule of
noisy machinery.
Controls, engineering —Any use of engineering methods to reduce or control the sound level
of a noise source by modifying or replacing equipment, making any physical changes at
the noise source or along the transmission path (with the exception of hearing protectors).
Criterion sound level— A sound level of 90 decibels.
dB ( decibel )—The unit used to express the intensity of sound. The decibel was named after
Alexander Graham Bell. The decibel scale is a logarithmic scale in which 0 dB approxi-
mates the threshold of hearing in the mid frequencies for young adults and in which the
threshold of discomfort is between 85 and 95 dB SPL and the threshold for pain is between
120 and 140 dB SPL.
Double hearing protection— A combination of both ear plug and ear muff type hearing pro-
tection devices is required for employees who have demonstrated temporary threshold
shift during audiometric examination and for those who have been advised by a medical
doctor to wear double protection in work areas that exceed 104 dBA.
Dosimeter —When applied to noise, refers to an instrument that measures sound levels over
a specified interval, stores the measurements, and calculates the sound as a function of
sound level and sound duration. It describes the results in terms of dose, time-weighted
average, and (perhaps) other parameters such as peak level, equivalent sound level, sound
exposure level, etc.
Equal-energy rule —The relationship between sound level and sound duration based upon a
3-dB exchange rate; that is, the sound energy resulting from doubling or halving a noise
exposure's duration is equivalent to increasing or decreasing the sound level by 3 dB,
resp e ct ively.
Exchange rate —The relationship between intensity and dose. OSHA uses a 5-dB exchange
rate. Thus, if the intensity of an exposure increases by 5 dB, the dose doubles. Sometimes
this is also referred to as the doubling rate. The U.S. Navy uses a 4-dB exchange rate;
the U.S. Army and Air Force uses a 3-dB exchange rate. NIOSH recommends a 3-dB
exchange rate. Note that the equal-energy rule is based on a 3-dB exchange rate.
Frequency— Rate in which pressure oscillations are produced. It is measured in hertz (Hz).
Hazardous noise —Any sound for which any combination of frequency, intensity, or duration
is capable of causing permanent hearing loss in a specified population.
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