FAQ Glossary
What are some of the basic acoustic terms?
What are all these acronyms?
What is the difference between diffusion, diffraction, reflection and refraction?
What is reverberation?
What are some of the terms regarding sound measurement?
What are the key phrases related to acoustics in architecturally designed spaces?
What are the meanings of the terms found on product information sheets?
What are some issues for schools, public building, and other common spaces?
What are the key phrases related to acoustics and noise in industrial environments?
What are key phrases related to acoustics in office environments?
What are some of the basic acoustic terms?
Absorption Coefficient (alpha)
-The dimensionless ration of absorbed to incident sound energy from a single interaction between a sound wave and a partition. Values range from 0 to 1.
Absorption
-The product of absorption coefficient and surface area of a material, in units of sabins, used to designate the amount of sound absorbed by that material.
-The properties of a material composition to convert sound energy into heat thereby reducing the amount of energy that can be reflected.
Acoustics
-The science or study of sound, its production, transmission and effects.
Attenuation
-The reduction of sound energy as a function of distance traveled.
Decibel (dB)
-A unit of sound level implying 10 multiplied by a logarithmic ration of power or some quantity proportional to power. The logarithm is to the base 10.
-Sound intensity is described in decibels. For example: breathing, 5 dB; office activity 50 dB; jet aircraft during takeoff at 300' distance, 130 dB.
Frequency (f)
-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.
-Interpreted subjectively as pitch. Humans can hear sounds having frequencies between 20 and 20,000 Hz.
Hertz (Hz)
-Frequency of sound expressed by cycles per second.
Noise
-Unwanted sound.
Noise Reduction Coefficient (NRC)
-A single number rating system for absorption coefficients over the speech frequency range.
The NRC of an acoustical material is the mathematical average to the absorption coefficients at 250,500,1000, 2000 Hz.
Pitch
-The perceived auditory sensation of sounds expressed in terms of high or low frequency stimulus of the sound.
Sound Absorption
-Property possessed by materials, objects and air to convert sound energy into heat. Sound waves reflected by a surface cause a loss of energy. That energy not reflected is called an absorption coefficient.
Sound Absorption Coefficient (SAC)
-The fraction of energy striking a material or object that is not reflected. For instance, if a material reflects 70% of the sound energy incident upon its surface, then its Sound Absorption Coefficient is 0.30.
-SAC = absorption / area in sabins per sq. ft.
Wavelength
-Distance between two identical positions in the cycle or wave. Sound that passes through air produces a wavelike motion of compression and refraction.
-Length of sound wave varies with frequency. Low frequency equals longer wavelengths.
What are all these acronyms?
Articulation Index (AI)
-A measure of speech intelligibility influenced by acoustical environment rated from 0.01 to 1.00. The higher the number the higher the intelligibility of words and sentences understood from 0 - 100%.
dBA
-A-weighted unit of sound pressure level.
Decibel (dB)
-A unit of sound level implying 10 multiplied by a logarithmic ration of power or some quantity proportional to power. The logarithm is to the base 10.
-Sound intensity is described in decibels. For example: breathing, 5 dB; office activity 50 dB; jet aircraft during takeoff at 300' distance, 130 dB.
Hertz (Hz)
-Frequency of sound expressed by cycles per second.
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 diminished sound level within a room caused by adding absorptive material to the room.
Noise Reduction Coefficient (NRC)
-A single number rating system for absorption coefficients over the speech frequency range.
The NRC of an acoustical material is the mathematical average to the absorption coefficients at 250,500,1000, 2000 Hz.
Sound Absorption Coefficient (SAC)
-The fraction of energy striking a material or object that is not reflected. For instance, if a material reflects 70% of the sound energy incident upon its surface, then its Sound Absorption Coefficient is 0.30.
-SAC = absorption / area in sabins per sq. ft.
Sound Transmission Class (STC)
-A single number rating for a transmission loss spectrum of a partition or barrier matched to a standard curve. These measurements are performed in laboratory-type environments.
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. Same as LOSHA.
Transmission Loss (TL)
-A measure of the sound attenuation effectiveness of a partition or barrier, in units of decibels.
What is the difference between diffusion, diffraction, reflection and refraction?
Diffraction
-The act of sound waves traveling around barriers especially pronounced when the sound wavelength size is comparable to or greater than the dimensions of the barriers.
Diffuse Field
-Area, within a room, where the sound pressure levels do not vary significantly with location.
-Caused by reverberation.
Diffusion
-The scattering or random reflection of a sound wave from a surface. The directions of reflected sound are changed so that listeners may have sensation of sound coming from all directions at equal levels.
Reflection
-The amount of sound wave energy (sound) that is reflected off a smooth, hard surface. Some sound reflection can enhance the quality of the signal of speech and music.
Refraction
-The act of sound waves bending or changing propagation direction as they travel from one medium or medium condition (such as temperature, density, humidity, or wind current) into another.
What is reverberation?
Echo
-Reflected sound producing a distinct repetition of the original sound.
-The perception of two distinct sounds resulting from the difference in arrival times of sound waves traveling over different paths but originating from a single source.
Reverberant Field
-Same as diffuse field
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.
-The amplification of sound within an enclosed space caused by multiple reflection off reflective surfaces (walls, ceilings, floors, etc.) of the room.
Reverberation Time (RT60 or T60)
-Time, in seconds, it takes for sound to decay 60 dB after the sound source has stopped. Sound after it has ended will continue to reflect off surfaces until the wave loses enough energy by absorption to eventually die out.
-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.
What are some of the terms regarding sound measurement?
Absorption
-The product of absorption coefficient and surface area of a material, in units of sabins, used to designate the amount of sound absorbed by that material.
-The properties of a material composition to convert sound energy into heat thereby reducing the amount of energy that can be reflected.
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 in the construction of the space.
-Also, a study of the amount of acoustical absorption required to reduce reverberation and noise.
Anechoic Chamber
-A room having terminations (walls, floor, and ceiling) that absorb all sound incident on them.
-Used in laboratories to measure direct sound fields from sources.
A-Weighted Sound Level
-A measure of sound pressure level designed to model the response of the human ear, which does not respond equally to all frequencies. The ear is less efficient at low and high frequencies than at medium or speech-range frequencies. To describe sound in a manner representative of the human ear's 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. Most measurements of occupational, industrial and environmental noise are taken using A-weighting.
dBA
-A-weighted unit of sound pressure level.
Decibel (dB)
-A unit of sound level implying 10 multiplied by a logarithmic ration of power or some quantity proportional to power. The logarithm is to the base 10.
-Sound intensity is described in decibels. For example: breathing, 5 dB; office activity 50 dB; jet aircraft during takeoff at 300' distance, 130 dB.
Frequency (f)
-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.
-Interpreted subjectively as pitch. Humans can hear sounds having frequencies between 20 and 20,000 Hz.
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.
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.
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 baffle tested through the standard range of 125 - 4000 Hz.
Sabine Formula
-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.
Sound Absorption Coefficient (SAC)
-The fraction of energy striking a material or object that is not reflected. For instance, if a material reflects 70% of the sound energy incident upon its surface, then its Sound Absorption Coefficient is 0.30.
-SAC = absorption / area in sabins per sq. ft.
Sound Level Meter
-Device that converts sound pressure variations in air into corresponding electronic signals. The signals are filtered to exclude signals outside frequencies desired.
Spectrum
-Graphic representation of sound level vs. frequency.
What are the key phrases related to acoustics in architecturally designed spaces?
Architectural Acoustics
-The control of noise and sound in a building space to adequately support the communication functions 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.
Background Noise Level
-The noise level in the acoustic environment, usually excluding the noise source of interest.
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.
Resonance (Acoustic or Room)
-The generation of standing waves within a space at specific frequencies that correlate certain fractions of wavelengths, and integer multiples of them, with the dimensions of the space.
Sound Level Meter
-Device that converts sound pressure variations in air into corresponding electronic signals. The signals are filtered to exclude signals outside frequencies desired.
Speech Privacy
-Degree to which speech is unintelligible between offices. Three ratings are used: Confidential, Normal (Non Obtrusive) and Minimal.
What are the meanings of the terms found on product information sheets?
Absorption Coefficient (alpha)
-The dimensionless ration of absorbed to incident sound energy from a single interaction between a sound wave and a partition. Values range from 0 to 1.
Absorption
-The product of absorption coefficient and surface area of a material, in units of sabins, used to designate the amount of sound absorbed by that material.
-The properties of a material composition to convert sound energy into heat thereby reducing the amount of energy that can be reflected.
Frequency (f)
-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.
-Interpreted subjectively as pitch. Humans can hear sounds having frequencies between 20 and 20,000 Hz.
Hertz (Hz)
-Frequency of sound expressed by cycles per second.
Noise Reduction Coefficient (NRC)
-A single number rating system for absorption coefficients over the speech frequency range.
The NRC of an acoustical material is the mathematical average to the absorption coefficients at 250,500,1000, 2000 Hz.
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 baffle tested through the standard range of 125 - 4000 Hz.
Sound Absorption Coefficient (SAC)
-The fraction of energy striking a material or object that is not reflected. For instance, if a material reflects 70% of the sound energy incident upon its surface, then its Sound Absorption Coefficient is 0.30.
-SAC = absorption / area in sabins per sq. ft.
What are some issues for schools, public building, and other common spaces?
Articulation Class
-A single number rating used for comparing acoustical ceilings and acoustical screens for speech privacy purposes. AC values increase with increasing privacy and range from approximately 100 - 250. This classification supersedes Speech Privacy Noise Isolation Class (NIC) rating method.
Articulation Index (AI)
-A measure of speech intelligibility influenced by acoustical environment rated from 0.01 to 1.00. The higher the number the higher the intelligibility of words and sentences understood from 0 - 100%.
Background Noise Level
-The noise level in the acoustic environment, usually excluding the noise source of interest.
Barrier
-A material that when placed around a source of noise inhibits the transmission of that noise beyond the barrier.
-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 so for persons with a hearing impairment.
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.
Direct Field
-Area where the sound measured can be attributed to the source alone without effects of reflections off of walls or obstructions.
Echo
-Reflected sound producing a distinct repetition of the original sound.
-The perception of two distinct sound resulting from the difference in arrival times of sound waves traveling over different paths but originating from a single source.
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.
Speech Privacy
-Degree to which speech is unintelligible between offices. Three ratings are used: Confidential, Normal (Non Obtrusive) and Minimal.
White Noise
-Sound characterized by having an equal amount of energy in each linear frequency band.
-A variation of white noise is pink noise which has equal energy per octave (logarithmic) frequency band.
What are the key phrases related to acoustics and noise in industrial environments?
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.
Barrier
-A material that when placed around a source of noise inhibits the transmission of that noise beyond the barrier.
-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 so for persons with a hearing impairment.
Direct Field
-Area where the sound measured can be attributed to the source alone without effects of reflections off of walls or obstructions.
Noise
-Unwanted sound.
Sound Level Meter
-Device that converts sound pressure variations in air into corresponding electronic signals. The signals are filtered to exclude signals outside frequencies desired.
Sound Transmission Class (STC)
-A single number rating for a transmission loss spectrum of a partition or barrier matched to a standard curve. These measurements are performed in laboratory-type environments.
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. Same as LOSHA.
Transmission Loss (TL)
-A measure of the sound attenuation effectiveness of a partition or barrier, in units of decibels.
What are key phrases related to acoustics in office environments?
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.
Masking
-The process by which the threshold of hearing of one sound is raised due to the presence of another.
-Adding acceptable sounds to an environment to cover unwanted sound and reduce annoyance.
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.
Sound Level Meter
-Device that converts sound pressure variations in air into corresponding electronic signals. The signals are filtered to exclude signals outside frequencies desired.
Speech Privacy
-Degree to which speech is unintelligible between offices. Three ratings are used: Confidential, Normal (Non Obtrusive) and Minimal.
White Noise
-Sound characterized by having an equal amount of energy in each linear frequency band.
-A variation of white noise is pink noise which has equal energy per octave (logarithmic) frequency band.
