Absorption
The properties of a material composition to convert
sound energy into heat thereby reducing the amount of
sound energy that can be reflected. |
Acoustical
The properties of a material to absorb or reflect sound
(adjective) acoustically, (adverb). |
Acoustical Analysis
A review of a space to determine the level or
reverberation or reflected sound in the space (in
seconds) as influenced by the building materials used to
construction the space. Also, a study of the amount of
acoustical absorption required to reduce reverberation
and noise. |
Acoustical Environment
The acoustical characteristics of a space or room
influenced by the amount of acoustical absorption, or
lack of it, in the space. |
Acoustics
Acoustics is the science of sound, including its
production, transmission and effects. The acoustics of a
room are those qualities that together determine its
character with respect to the perception of sound.
|
Ambient
Noise
Ambient noise encompasses all sound present in a given
environment, being usually a composite of sounds from
many sources near and far. |
Architectural Acoustics
The control of noise in a building space to adequately
support the communications function within the space and
its effect on the occupants. The qualities of the
building materials used to determine its character with
respect to distinct hearing. |
Area
Effect
Acoustical materials spaced apart can have greater
absorption than the same amount of material butted
together. The increase in efficiency is due to
absorption by soft exposed edges and also to diffraction
of sound energy around panel perimeters. |
Attenuation
The reduction of sound energy as a function of distance
traveled. |
Audiometer
An instrument for measuring hearing acuity. |
A-Weighted Sound Level
A measure of sound pressure level designed to reflect
the response of the human ear, which does not respond
equally to all frequencies. To describe sound in a
manner representative of the human ears response it is
necessary to reduce the effects of the low and high
frequencies with respect to the medium frequencies. The
resultant sound level is said to be A-weighted, and the
units are dBA. The A-weighted sound level is also called
the noise level. Sound level meters have an A-weighting
network for measuring A-weighted sound levels.
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Baffle
A free hanging acoustical sound absorbing unit. Normally
suspended vertically in a variety of patterns to
introduce absorption into a space to reduce
reverberation and noise levels. |
Boominess
Low frequency reflections. In small rooms, acoustical
panels with air space behind can better help control low
frequency reflectivity. |
Cloud
In acoustical industry terms, an acoustical panel
suspended in a horizontal position from ceiling/roof
structure. Similar to a baffle but in a horizontal
position. |
Cocktail
Party Effect
Sound in a noisy crowded room generated mostly by
conversation. Levels rise and fall as people compete
with one another to be heard. Perception of speech can
be nearly impossible in high levels of noise.
|
Cycle
In acoustics, the cycle is the complete oscillation of
pressure above and below the atmospheric static
pressure. |
Damping
Damping is the dissipation of vibratory energy in solid
media and structures with time or distance. It is
analogous to the absorption of sound in air.
|
Decibel
(dB)
A dimensionless unit which denotes the ratio between two
quantities that are proportional to power, energy or
intensity. One of these quantities is a designated
reference by which all other quantities of identical
units are divided. The sound pressure level in decibels
is equal to 10 times the logarithm (to the base 10) of
the ratio between the pressure squared divided by the
reference pressure squared. The reference pressure used
in acoustics is 20 microPascals. |
Diffusion
The scattering or random reflection of a sound wave from
a surface. The directions of reflected sound is changed
so that listeners may have sensation of sound coming
from all directions at equal levels. |
Echo
Reflected sound producing a distinct repetition of the
original sound. Echo in mountains is distinct by reason
of travel after original signal has ceased. |
Field
Impact Insulation Class (FIIC)
When measurements are conducted in buildings according
to the appropriate standards for field measurements,
impact insulation class is called field impact
insulation class (FIIC). The field test evaluates the
dwellings actual construction and includes all sound
paths. |
Field
Sound Transmission Class (FSTC)
When measurements are conducted in buildings according
to the appropriate standards for field measurements,
sound transmission class is called field sound
transmission class (FSTC). The field test evaluates the
dwellings actual construction and includes all sound
paths. |
Flanking
The transmission of sound around the perimeter or
through holes within partitions (or barriers) that
reduces the otherwise obtainable sound transmission loss
of a partition. Examples of flanking paths within
buildings are ceiling plena above partitions; ductwork,
piping, and electrical conduit penetrations through
partitions; back-to-back electrical boxes within
partitions, window mullions, etc. |
Flutter
Echo
Short echoes in small reverberative spaces that produce
a clicking, ringing or hissing sound after the original
sound signal has ceased. Flutter echoes may be present
in long narrow spaces with parallel walls. |
Free
Field
Sound waves from a source outdoors where there are no
obstructions. |
Frequency
The number of oscillations or cycles per unit of time.
Acoustical frequency is usually expressed in units of
Hertz (Hz) where one Hz is equal to one cycle per
second. |
Frequency Analysis
An analysis of sound to determine the character of the
sound by determining the amount of sounds at various
frequencies that make up the overall sound spectrum. For
example, higher frequency sound or pitch vs. low
frequency. |
Hearing
Impairment
A degree of hearing loss, temporary or permanent, due to
many causes. Hearing loss can be caused by illness,
disease, or exposure to excessively high noise levels.
Affects 25 50 million people in USA of all ages.
Hearing impairment as generally used means a hearing
loss of mild, moderate or severe degree as opposed to
deafness which is generally described as little or no
residual hearing with or without the aid of an assistive
listening device. Hearing impaired persons are
particularly adversely affected by long reverberation
times. |
Hearing
Range
16 2000 Hz (Speech Intelligibility) 600 4800 Hz
(Speech Privacy) 250 2500 Hz (Typical small table
radio) |
Hertz
(Hz)
Frequency of sound expressed by cycles per second. (See
Cycle). |
Impact
Insulation Class (IIC)
Rates a floor/ceiling assembly's ability to block impact
sound. Impact Insulation Class (sometimes referred to as
Impact Isolation Class) measures a floor/ceiling
assemblys resistance to the transmission of
structure-borne or impact noise, like human footfall.
The tapping machine frequently used for this test is not
designed to simulate any one type of impact, such as
male or female footsteps, or to simulate the weight of a
human walker. Thus the subjectively annoying creak or
boom generated by human footfalls on a limber floor
assembly may not be adequately evaluated by this method
(American Society for Testing and Materials ASTM, E
1007, 5.2). |
Intensity
See Loudness |
Inverse
Square Law
Sound levels fall off with distance traveled. Sound
level drops off 6 dB from the source point for every
doubling of distance. |
Live
End/Dead End
An acoustical treatment plan for rooms in which one end
is highly absorbent and the other end is reflective and
diffusive. |
Loudness
A listeners auditory impression of the strength of a
sound. The average deviation above and below the static
value due to a sound wave is called sound pressure. The
energy expended during the sound wave vibration is
called intensity and is measured in intensity units.
Loudness is the physical resonance to sound pressure and
intensity. |
Masking
The process by which the threshold of hearing of one
sound is raised due to the presence of another.
|
Mass
Mass is the fundamental property of a material relevant
to sound transmission loss through that material.
Generally, the more massive the material, the greater
the sound transmission loss. |
Mounting
Standards established by ASTM to represent typical
installation for purpose of testing materials. For
example, a mounting test specimen is mounted directly
the test room surface or furred out to produce an air
space behind. |
Noise
Unwanted sound that is annoying or interferes with
listening. Not all noise needs to be excessively loud to
represent an annoyance or interference. |
Noise
Criteria (NC)
Noise criteria curves used to evaluate existing
listening conditions at ear level by measuring sound
levels at the loudest locations in a room. NC criteria
can be referred to equivalent dBA levels. |
Noise
Isolation Class (NIC)
A single number rating of the degree of speech privacy
achieved through the use of an Acoustical Ceiling and
sound absorbing screens in an open office. NIC has been
replaced by the Articulation Class (AC) rating method.
|
Noise
Reduction (NR)
The amount of noise that is reduced through the
introduction of sound absorbing materials. The level (in
decibels) of sound reduced on a logarithmic basis.
|
Noise
Reduction Coefficient (NRC)
The NRC of an acoustical material is the arithmetic
average to the nearest multiple of 0.05 of its
absorption coefficients at 4 one-third octave bands with
center frequencies of 250, 500, 1000, 2000 Hertz. The
NRC rating can be viewed as a percentage (example: .80 =
80%) of what soundwaves that come in contact with the
acoustical material are absorbed by the material and NOT
reflected back within the room. |
Octave
A pitch interval of 2 to 1. The tone whose frequency is
twice that of the given tone. |
Octave
Bands
Sounds that contain energy over a wide range of
frequencies are divided into sections called bands. A
common standard division is in 10 octave bands
identified by their center frequencies 31.5, 63, 250,
500, 1000, 2000, and 4000 Hz |
Pitch
The perceived auditory sensation of sounds expressed in
terms of high or low frequency stimulus of the sound.
|
Reflection
The amount of sound wave energy (sound) that is
reflected off a surface. Hard non-porous surfaces
reflect more sound that soft porous surfaces. Some sound
reflection can enhance the quality of the signal of
speech and music. |
Resonance
The emphasis of sound at a particular frequency.
|
Reverberation
Sound after it is ended at the source will continue to
reflect off surfaces until the sound wave loses energy
by absorption to eventually die out |
Reverberation Time
The reverberation time of a room is the time it takes
for sound to decay by 60 dB once the source of sound has
stopped. Reverberation time is the basic acoustical
property of a room which depends only on its dimensions
and the absorptive properties of its surfaces and
contents. Reverberation has an important impact on
speech intelligibility. |
Sabin
A unit of sound absorption based on one square foot of
material. Baffles are frequently described as providing
X number of sabins of absorption based on the size of
the panel tested through the standard range of 125
4000 Hz. The number of sabins developed by other
acoustical materials are determined by the amount of
material used and its absorption coefficients.
|
Sabine
Formula
A formula developed by Wallace Clement Sabine that
allows designers to plan reverberation time in a room in
advance of construction and occupancy. Defined and
improved empirically, the Sabine Formula is T=0.049(V/A)
where T=Reverberation time (time required for sound to
decay 60 dB after source has stopped) in seconds.
V=Volume of room in cubic feet. A=total square footage
of absorption in sabins. |
Septum
A thin layer of material between 2 layers of absorptive
material, such as foil, lead, steel, etc. that prevents
sound wave from passing through absorptive material.
|
Signal
to Noise Ratio
The sound level at the listeners ear of a speaker above
the background noise level. The inverse square law
impacts the S/N ratio. |
Sound
Sound is an oscillation in pressure, stress particle
displacement, particle velocity in a medium. Sound
produces an auditory sensation caused by the
oscillation. |
Sound
Absorption
The property possessed by materials, objects and air to
convert sound energy into heat. Sound waves reflected by
a surface causes a loss of energy. That energy not
reflected is call is absorption coefficient.
|
Sound
Absorption Coefficient
The fraction of energy striking a material or object
that is not reflected. For instance, if a material
reflects70% of the sound energy incident upon its
surface, then its Sound Absorption Coefficient would be
0.30. SAC=absorption/area in sabins per sq. ft.
|
Sound
Barrier
A material that when placed around a source of noise
inhibits the transmission of that noise beyond the
barrier. Also, anything physical or an environment that
interferes with communication or listening. For example,
a poor acoustical environment can be a barrier to good
listening and especially for persons with a hearing
impairment. |
Sound
Level
A subjective measure of sound expressed in decibels as a
comparison corresponding to familiar sounds experienced
in a variety of situations. |
Sound
Level Meter
A device that converts sound pressure variations in air
into corresponding electronic signals. The signals are
filtered to excluded signals outside frequencies
desired. |
Sound
Pressure
The sound pressure is the total instantaneous pressure
at a point in space, in the presence of a sound wave,
minus the static pressure at that point. |
Sound
Pressure Level
The sound pressure level, in decibels, of a sound is 20
time the logarithm to the base of 10 of the ratio of the
sound pressure to the reference pressure. The reference
pressure shall be explicitly stated and is defined by
standard. |
Sound
Transmission Class (STC)
This is a rating for doors, windows, enclosures, noise
barriers, partitions and other acoustical products. The
rating is in terms of their relative ability to provide
privacy against intrusion of speech sounds. This is a
one number rating system, heavily weighted in the 500Hz
to 2000Hz frequency range where speech intelligitibility
largely occurs. |
Spectrum
The description of a sound waves components of
frequency and amplitude. |
Speech
Intelligibility
The ability of a listener to hear and correctly
interpret verbal messages. In a classroom with high
ceilings and hard parallel surfaces such as glass and
tile, speech intelligibility is a particular problem.
Sound bounces off walls, ceilings and floors, distorting
the teachers instructions and interfering with
students ability to comprehend. Centers between 250 and
4000k. |
Speech
Privacy
The degree to which speech is unintelligible between
offices. Three ratings are used: Confidential, Normal
(Non Obtrusive) and Minimal. |
Time
Weighted Average (TWA)
The yardstick used by the Occupational Safety and Health
Administration (OSHA) to measure noise levels in the
workplace. It is equal to a constant sound level lasting
eight hours that would cause the same hearing damage as
the variable noises that a worker is actually exposed
to. (This hearing loss, of course, occurs over long-term
exposures.) Same as LOSHA. |
Ultrasounds
Sounds of a frequency higher than 20,000 Hz. The
frequency region containing these frequencies is called
the ultrasonic region. |
Volume
The cubic space of a room bounded by walls, floors, and
ceilings determined by the Volume=Length x Width x
Height of space. Volume influences reverberation time.
|
Wavelength
Sound that passes through air produces a wavelike motion
of compression and refraction. Wavelength is the
distance between two identical positions in the cycle or
wave. Similar to ripples or waves produces by dropping a
stone in water. Length of sound wave varies with
frequency. Low frequency equals longer wavelengths.
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