Acoustic Terminology
Absorbent
A material into which sound is absorbed.
Absorb
To take in, retain, or bind. For example, an acoustic material absorbs sound, reducing its level.
Absorption
The process by which sound is absorbed into a material.
Absorption Area
The absorption area is calculated as the surface area multiplied by its absorption coefficient (absorbing surface area × absorption coefficient).
For example, if 10 m² of material with an absorption coefficient of 0.8 is installed in a room, the absorption area is 8 m².
When the absorption area and room volume are known, the reverberation time can be approximately calculated using Sabine’s formula.
Absorption Coefficient
A measure of a material’s ability to absorb sound. A highly sound-absorbing material typically has an absorption coefficient greater than 0.8 across a wide frequency range. Absorption coefficients are used to calculate reverberation times.
Absorption Class
Sound-absorbing panels are classified into absorption classes A–E according to the EN ISO 11654 standard. Sound absorption is measured at frequencies between 200–5000 Hz.
Acoustics
A branch of physics that studies sound. It includes all physical phenomena perceived by humans through hearing. The word acoustics originates from the Greek akoustikos (relating to hearing) and akouo (to hear).
Amplitude
The peak value of sound pressure in a sound wave.
Articulation Index (AI)
An acoustic parameter describing speech intelligibility.
Articulation Class (AC)
Acoustic privacy between workstations in open-plan offices is expressed using the articulation class (AC). It is calculated based on sound attenuation within the space. The higher the AC value, the better the acoustic privacy. Good privacy requires an AC value of at least 180.
Background Noise
Disturbing, non-informative sound generated, for example, by ventilation systems. High background noise levels may cause long-term effects such as fatigue, nausea, and reduced efficiency and productivity.
Building Acoustics
The study of sound behaviour in buildings, often focusing on sound transmission between spaces, i.e. sound insulation.
Decibel (dB)
The unit of sound pressure level. A change of 10 decibels is perceived as a doubling or halving of loudness.
Frequency
The number of vibrations per second, measured in hertz (Hz). Higher frequencies correspond to higher-pitched sounds, while lower frequencies correspond to lower-pitched sounds.
The human hearing range is approximately 20–20,000 Hz. Speech frequencies typically range from 125–8000 Hz.
Flutter Echo
A rapidly repeating echo that occurs when sound waves travel between parallel surfaces.
Noise
Unwanted or disturbing sound. A subjective concept.
Porous Absorbers
Porous absorbers have a surface through which sound waves can pass, with interconnected pores. Sound energy is reduced through internal friction and converted into heat. Typical porous absorbers include mineral wool, foam, and fabric-based products.
Room Acoustics
Room acoustics studies the behaviour of sound within enclosed spaces. The key parameter is reverberation time, which describes how echoic a room is.
Reverberation Time
The time it takes for the sound level to decrease by 60 dB after the sound source has stopped. Long reverberation times are perceived as echo. In well-damped spaces, reverberation time is around 0.4 seconds, while in highly reverberant spaces (e.g. churches) it may exceed 10 seconds. Reverberation time can be approximated using Sabine’s formula.
Psychoacoustics
The study of how individuals perceive sound. Psychoacoustic experiences are subjective and relate to personal responses to the sound environment.
Speech Intelligibility
Speech intelligibility depends on background noise level, reverberation time, and room geometry.
Resonance
Occurs when sound reflects between two opposing surfaces. Resonances (standing waves or room modes) form along the length, width, and height of a room—between end walls, side walls, and between the floor and ceiling.
Resonant Absorption
Resonators operate based on resonant vibration. Examples include perforated resonators and membrane resonators.
Sabine’s Formula
Describes the relationship between reverberation time (T, s), room volume (V, m³), and absorption area (A, m²).
The reverberation time can be approximated using the formula:
T = 0.16 × V / A
Hall Acoustics
The acoustics of large spaces such as concert halls.
Reflection
A rapid change in the direction of a sound wave when it encounters a boundary surface.
Sound Insulation
The ability of a structure to prevent sound from being transmitted from one space to another or through the structure.
Sound Pressure
Fluctuations in air pressure caused by sound waves are called sound pressure (Lp). The unit of sound pressure level is decibels (dB).
The lowest audible sound pressure level is the threshold of hearing (0 dB). Sounds above approximately 120 dB exceed the pain threshold.
Sound Absorption
Sound absorption refers to the conversion of sound energy into another form of energy, usually heat, as sound travels through a medium. Sound-absorbing materials and structures reduce reflections, lower noise levels, and shorten reverberation time.
Sound Absorption Class
Sound-absorbing panels are classified into absorption classes A–E according to EN ISO 11654. Measurements are conducted at frequencies between 200–5000 Hz. Class A products provide the highest absorption performance.
Sound Level (Lp)
A synonym for sound pressure level. Measured in decibels (dB) at different frequencies.
Sound
Vibration that propagates through a medium and produces an auditory sensation.
Standing Waves
Standing waves (also called resonances or room modes) occur when sound reflects between opposing surfaces in a room.
A material into which sound is absorbed.
Absorb
To take in, retain, or bind. For example, an acoustic material absorbs sound, reducing its level.
Absorption
The process by which sound is absorbed into a material.
Absorption Area
The absorption area is calculated as the surface area multiplied by its absorption coefficient (absorbing surface area × absorption coefficient).
For example, if 10 m² of material with an absorption coefficient of 0.8 is installed in a room, the absorption area is 8 m².
When the absorption area and room volume are known, the reverberation time can be approximately calculated using Sabine’s formula.
Absorption Coefficient
A measure of a material’s ability to absorb sound. A highly sound-absorbing material typically has an absorption coefficient greater than 0.8 across a wide frequency range. Absorption coefficients are used to calculate reverberation times.
Absorption Class
Sound-absorbing panels are classified into absorption classes A–E according to the EN ISO 11654 standard. Sound absorption is measured at frequencies between 200–5000 Hz.
Acoustics
A branch of physics that studies sound. It includes all physical phenomena perceived by humans through hearing. The word acoustics originates from the Greek akoustikos (relating to hearing) and akouo (to hear).
Amplitude
The peak value of sound pressure in a sound wave.
Articulation Index (AI)
An acoustic parameter describing speech intelligibility.
Articulation Class (AC)
Acoustic privacy between workstations in open-plan offices is expressed using the articulation class (AC). It is calculated based on sound attenuation within the space. The higher the AC value, the better the acoustic privacy. Good privacy requires an AC value of at least 180.
Background Noise
Disturbing, non-informative sound generated, for example, by ventilation systems. High background noise levels may cause long-term effects such as fatigue, nausea, and reduced efficiency and productivity.
Building Acoustics
The study of sound behaviour in buildings, often focusing on sound transmission between spaces, i.e. sound insulation.
Decibel (dB)
The unit of sound pressure level. A change of 10 decibels is perceived as a doubling or halving of loudness.
Frequency
The number of vibrations per second, measured in hertz (Hz). Higher frequencies correspond to higher-pitched sounds, while lower frequencies correspond to lower-pitched sounds.
The human hearing range is approximately 20–20,000 Hz. Speech frequencies typically range from 125–8000 Hz.
Flutter Echo
A rapidly repeating echo that occurs when sound waves travel between parallel surfaces.
Noise
Unwanted or disturbing sound. A subjective concept.
Porous Absorbers
Porous absorbers have a surface through which sound waves can pass, with interconnected pores. Sound energy is reduced through internal friction and converted into heat. Typical porous absorbers include mineral wool, foam, and fabric-based products.
Room Acoustics
Room acoustics studies the behaviour of sound within enclosed spaces. The key parameter is reverberation time, which describes how echoic a room is.
Reverberation Time
The time it takes for the sound level to decrease by 60 dB after the sound source has stopped. Long reverberation times are perceived as echo. In well-damped spaces, reverberation time is around 0.4 seconds, while in highly reverberant spaces (e.g. churches) it may exceed 10 seconds. Reverberation time can be approximated using Sabine’s formula.
Psychoacoustics
The study of how individuals perceive sound. Psychoacoustic experiences are subjective and relate to personal responses to the sound environment.
Speech Intelligibility
Speech intelligibility depends on background noise level, reverberation time, and room geometry.
Resonance
Occurs when sound reflects between two opposing surfaces. Resonances (standing waves or room modes) form along the length, width, and height of a room—between end walls, side walls, and between the floor and ceiling.
Resonant Absorption
Resonators operate based on resonant vibration. Examples include perforated resonators and membrane resonators.
Sabine’s Formula
Describes the relationship between reverberation time (T, s), room volume (V, m³), and absorption area (A, m²).
The reverberation time can be approximated using the formula:
T = 0.16 × V / A
Hall Acoustics
The acoustics of large spaces such as concert halls.
Reflection
A rapid change in the direction of a sound wave when it encounters a boundary surface.
Sound Insulation
The ability of a structure to prevent sound from being transmitted from one space to another or through the structure.
Sound Pressure
Fluctuations in air pressure caused by sound waves are called sound pressure (Lp). The unit of sound pressure level is decibels (dB).
The lowest audible sound pressure level is the threshold of hearing (0 dB). Sounds above approximately 120 dB exceed the pain threshold.
Sound Absorption
Sound absorption refers to the conversion of sound energy into another form of energy, usually heat, as sound travels through a medium. Sound-absorbing materials and structures reduce reflections, lower noise levels, and shorten reverberation time.
Sound Absorption Class
Sound-absorbing panels are classified into absorption classes A–E according to EN ISO 11654. Measurements are conducted at frequencies between 200–5000 Hz. Class A products provide the highest absorption performance.
Sound Level (Lp)
A synonym for sound pressure level. Measured in decibels (dB) at different frequencies.
Sound
Vibration that propagates through a medium and produces an auditory sensation.
Standing Waves
Standing waves (also called resonances or room modes) occur when sound reflects between opposing surfaces in a room.
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