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A
Acoustics is the science of sound including its production,
transmission, and effects.
Action Level is an 8-hour TWA of 85 dBA measured on the
A-scale, slow response, or equivalently, a dose of 50 percent.
Acuity is the ability to discriminate between the two
different stimuli at levels above threshold.
Administrative Control is any procedure that limits daily
noise exposure by control of the work schedule.
Air-Bone Gap is the difference in decibels (at a specified
frequency) between the hearing threshold level for air conduction
and for bone conduction.
Air Conduction refers to the pathway by which sound waves
normally reach the inner ear; i.e., via the external meatus,
tympanic membrane, and ossicular chain.
Ambient Noise is background noise associated with a
given environment, being usually a composite of sounds from
many sources near and far.
Artificial Ear is a device for calibrating audiometer
earphones, and consists of a coupler and laboratory standard
microphone.
Attenuation is a reduction of sound energy. Thus, a sound
that is attenuated by 10 dB has been made 10 dB weaker (less
intense).
Audiogram is a chart, graph, or table resulting from
an audiometric test showing an individual's hearing threshold
levels as a function of frequency.
Audiologist is a professional specializing in the study
and habilitation of hearing, who is certified by the American
Speech-Language-Hearing Association, or licensed by a state
board of examiners.
Audiology is an interdisciplinary professional area
dealing with the measurements and interpretation of normal
or impaired hearing.
Audiometer is an electronic instrument for measuring
hearing threshold levels. Measurements may be made with pure
tone or speech.
Audiometric Zero (or 0 dB hearing threshold level) is
a set of values representing average normal hearing thresholds
for healthy young adult ears.
Auricle (or Pinna) is the most visible part of the ear,
is an ovoid, skin-covered, fibrocartilaginous plate that is
attached to the head. The auricle is believed to be most useful
in the gathering and localization of sound.
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B
Baseline Audiogram is the audiogram against which
future audiograms are compared.
Biological (Functional) Calibration Check is the audiometric
testing of one or more tinnitus-free individuals(s), having
a known stable hearing level that preferably does not exceed
25 dB at any test frequency between 500 and 6000 Hz, used
for the purpose of assessing the calibration of the audiometer.
Bone Conduction is the process by which sound is conducted
to the inner ear through the cranial bones. Bone conduction
threshold is a direct measure of the sensorineural components
of the hearing mechanism, relatively unaffected by the condition
of the conductive mechanism.
Bone-Conduction Vibrator is an electromechanical transducer
used with an audiometer to measure bone-conduction thresholds.
The device is held against the mastoid process by a flexible
metal headband.
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C
Certified Hearing Conservation Technician is an individual
who can show documentary evidence of the satisfactory completion
of a course of training meeting the minimum standards specified
by the Council for Accreditation in Occupational Hearing Conservation.
These technicians are certified only for pure-tone, air-conduction
hearing testing in support of a hearing conservation program.
Cerumen is a wax secreted in the outer portion of the
external auditory meatus. Its purpose is to discourage the
entry of insects and to keep the skin of the canal and drum
membrane moist and clean.
Cochlea is a spirally coiled, tapered bony tube of
about 2 3/4 turns located in the inner ear. It contains the
receptor organs essential to hearing.
Conductive Hearing Loss is produced by lesions of the
external and/or middle ear. The audiogram in such a loss is
characterized by normal bone-conduction thresholds, but depressed
air conduction (sometimes referred to as the "air-bone"
gap).
Coupler is a cavity of predetermined shape used in
the calibration of earphones. It couples the earphone under
calibration to a laboratory standard microphone.
Crest Factor is the absolute value of the ratio of the
peak value and the root-mean square value measured over a
specified time interval where both values are measured in
reference to the arithmetic mean value of the wave.
Criterion Sound Level is a sound level of 90 decibels.
Cross-Hearing occurs during a hearing test when tones
delivered to one ear are carried either around or through
the head in sufficient intensity to stimulate the opposite
ear.
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D
dBA is a sound level reading in decibels made on the
A-weighted network of a sound level meter at slow response.
dBC is a sound level reading in decibels made on the
C-weighted network of a sound level meter.
dBP is used to express peak sound pressure level of
impulse/impact noise. The peak instantaneous pressure is expressed
in decibels, using a reference of 20 µPa.
Deafness is the otological condition in which the hearing
threshold level for speech, or the average hearing threshold
level for tones 500, 1000, 2000, and 3000 Hz, is at least
93 decibels (re: ANSI S3.6-1969).
Decibel (dB) is a unit of measurement of sound level.
Director is Director of the National Institute for
Occupational Safety and Health, US Department of Health and
Human Resources.
Distortion is the failure of a communications system (or
an electronic system) to reproduce the transmitted wave form
with exactness.
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E
Effective Sound Level
For individuals not wearing hearing protective devices,
the workplace sound level.
For individuals wearing hearing protective devices, the
result of subtracting the effective reduction of the particular
hearing protective device in use from the measured workplace
sound level.
Engineering Control is any procedure, other than administrative
control or personal protection, that reduces the sound level
either at the source of the noise or within the hearing zone
of individuals.
Eustachian Tube is a canal that connects the middle
ear with the nasal part of the pharynx. It serves to equalize
the air pressure on the two sides of the tympanic membrane,
provides oxygen to the middle ear cavity and serves as a drain
for fluid accumulated in the middle ear cavity.
External Auditory Meatus (or ear canal) is the canal that
conducts sound vibrations from the auricle to the tympanic
membrane.
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F
Filter is a device for separating components of a
waveform on the basis of their frequency. Commonly used filters
include the octave-band, the one-third octave band, and narrow-band
filters.
Frequency is the rate of repetition of the cycles of
a sound wave. The units is the hertz (Hz); but it has been
called, until recently, cycles per second (cps). Frequency
of tone largely determines the pitch.
Frequency Analysis is the use of an instrument such as
an octave-band analyzer to measure the distribution of sound
energy throughout the audible spectrum.
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H
Hair Cells are the sensory receptor cells for hearing.
They are ciliated epithelial cells located within the cochlea
on the organ of Corti.
Hearing Loss (Impairment) is a term denoting an impairment
of auditory sensitivity. The amount of hearing impairment,
in decibels, is measured as a set of hearing threshold levels
at specified frequencies.
Hearing Threshold Level (HTL) for a sound is the difference
in decibels between the threshold for that sound and the corresponding
normal threshold or audiometric zero.
Hertz (Hz) is a unit of measurement of frequency, numerically
equal to cycles per second.
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I
Impulse or Impact Noises are those variations in noise
levels that involve brief maxima at intervals greater than
500 milliseconds. Where the intervals are less than 500 milliseconds,
the noise is considered continuous.
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L
Listening (Functional) Checks are the preliminary
checks of the audiometer to detect noise, distortion, intermittent
tones, and other audiometer malfunctions which would preclude
valid testing.
Logarithm is a mathematical device used to compress
a wide range of values of sound intensities into a simple,
manageable range from 0 dB to over 190 dB. (See Decibel).
Loudness is the intensive attribute of an auditory
sensation, in terms of which sounds may be ordered on a scale
extending from soft to loud.
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M
Masking is the amount of decibels, by which the threshold
of audibility of a sound is raised by the presence of another
(masking) sound. In audiometry, masking noise is used whenever
lateralization occurs and usually when obtaining bone-conduction
thresholds.
Medical Pathology is a disorder or disease. For purposes
of this regulation, a condition or disease affecting the ear,
which should be treated by a physician or specialist.
Monitoring Audiogram is any audiogram which can be
compared with the baseline (reference) audiogram. Its purpose
is to detect any change in hearing threshold levels.
Monitoring Hearing Tests are periodic hearing tests,
obtained subsequent to the reference hearing test, which are
used to detect shifts in the individual's threshold of hearing.
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N
Noise is any unwanted sound.
Noise Dose is the ratio, expressed as a percentage,
of (1) the time integral, over a stated time or event of the
0.6 power of the measured SLOW exponential time-averaged,
squared A-weighted sound pressure and (2) the product of the
criterion duration (8-hours) and the 0.6 power of the squared
sound pressure corresponding to the criterion sound level
(90 dB).
Noise Dosimeter is an instrument that integrates a
function of sound pressure over a period of time in such a
manner that it directly indicates a noise dose.
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O
Octave is the interval between two tones that are
separated by a frequency ratio of 2:1.
Ossicles are the three small bones in the middle ear,
i.e., the malleus (hammer), the incus (anvil), and the stapes
(stirrup). The bones transmit sound vibrations from the tympanic
membrane to the cochlea.
Otolaryngologist is a physician specializing in diagnosis
and treatment of disorders of the ear, nose, and throat.
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P
Patterning in audiometry is the presentation of test
tones in a rhythmical sequence and should be avoided.
Period is the time required for a sound wave to complete
one cycle. Period and frequency are inversely related.
Phase is the difference, in time, between two separate
tone sources of the same frequency.
Pitch is that attribute of auditory sensation in terms
of which sounds may be ordered on a scale extending from low
to high. Pitch depends primarily upon the frequency of the
sound stimulus, but also depends upon the sound pressure and
waveform of the stimulus.
Presbycusis is the loss of hearing associated with
aging.
Pure Tone is a sound wave of a single-frequency component
whose sound sensation is characterized by its singleness of
pitch.
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R
Reference (Baseline) Audiogram is the first audiogram
obtained for hearing conservation purposes against which all
monitoring audiometry is compared in the detection of significant
threshold shift. This audiogram must be obtained when the
individual is free from auditory fatigue and other transient
otologic pathology (also see Baseline Audiogram).
Reference (Baseline) Hearing Test is a hearing test performed
when an individual is not experiencing a temporary threshold
shift in hearing or other transient otologic pathology. The
resulting audiogram will be used as a reference in computing
any possible future threshold shift. Normally, this reference
audiogram will be the first performed for hearing conservation
purposes.
Representative Exposure are the measurements of an employee's
noise dose or 8-hour time-weighted average sound level that
the employers deem to be representative of the exposures of
other employees in the workplace.
Resonance is a condition whereby a vibrating air column,
string, membrane, rod, or an electronic circuit (oscillator)
is excited by an energy source at or near the same frequency
of the mechanical or electrical system.
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S
Screening Audiogram is any audiogram that is used
to separate individuals whose thresholds lie above/below a
given level.
Sensitivity is synonymous with hearing threshold.
Sensori-Neural Hearing Loss (Perceptive Loss) is produced
by lesions of the inner ear (cochlea) and/or the neural pathways
to the brain. The audiogram in such a loss is characterized
by depressed air-conduction and bone-conduction thresholds
of generally equal amounts.
Sound is an oscillation in pressure or molecular vibration
in an elastic media (air, water, metals, etc.) that results
in a transmission of vibratory energy in a wave-like manner.
It is also the auditory sensation evoked by such an oscillation.
Sound Level is ten times the common logarithm of the
ratio of the square of the measured A-weighted sound pressure
to the square of the standard reference pressure of 20 micropascals.
Unit: decibels (dB). For use with this regulation, SLOW time
response, in accordance with ANSI S1.4-1971 (R1976), is required.
Sound Level Meter is an instrument for the measuring
of sound level.
Sound Pressure Level (SPL) is the term used to identify
a sound measurement in decibels obtained with a sound level
meter that has a flat frequency response; e.g., 64 dB SPL.
It is understood that the value indicated by the measurement
is 20 times the logarithm of the ratio of the measured sound
pressure to the reference pressure (0 dB SPL = 20µN/m2,
µPa, 0.0002 dyne/cm2 or 0.0002 µbar).
Speech Frequencies extend from below 100 Hz to over
10,000 Hz, although the most significant range includes 300
Hz to 3000 Hz.
Spectrum is the range or mixture of frequencies comprising
a complex sound.
Standard Reference Level is an arbitrary level used as
a starting point on a scale of SPL or hearing level. In acoustics,
the reference sound pressure level (0 dB SPL) is 20 µPa.
In audiometry, the reference level for each frequency (0 dB
HTL) is average normal hearing of health young adult ears.
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T
Temporary Threshold Shift (TTS) is a change in hearing
threshold primarily due to exposure to high intensity noise
that usually can recover in 14 to 72 hours away from noise
exposure. Any loss that remains after a lengthy recovery period
is termed permanent threshold shift (PTS).
Threshold of Hearing is the lowest intensity of sound
that is capable of evoking an auditory sensation in a specified
fraction of trials (usually 50 percent or more).
Time-Weighted Average Sound Level is that sound level,
which if constant over an 8-hour exposure, would result in
the same noise dose as is measured.
Tinnitus is a ringing sensation perceived in the absence
of an acoustic stimulus.
Transducer is an electromechanical device that can
convert electrical energy to acoustical energy; e.g., earphone
or loudspeaker.
Tympanic Membrane (eardrum) is the conically-shaped semi-transparent
membrane that separates the external auditory meatus from
the middle ear cavity and transmits sound vibrations to the
ossicles.
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U
Ultrasonic Frequency is a frequency lying above the
audible frequency range.
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W
White Noise is a sound or electrical wave having a
continuous spectrum, uniform with frequency (analogous to
white light). It is sometimes used as a masking agent in audiometry.
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