Acoustic Glossary


Sound Absorption Terms and Definitions ...

Sound Absorption, sound energy is 'absorbed' by the different media that sound waves encounter, along their transmission path, from the source to the receiver.

An open window is an example of 100% sound absorption i.e. no reflection, whereas bathrooms usually have sound reflective surfaces and therefore very low sound absorption properties, resulting in multiple reflections in the room and a diffused sound field.

Sound Absorption is the product of sound absorption coefficient and surface area of a material, the units are Sabins.

Sound Absorption Definition (ASA 10.01) at a specified frequency or specified frequency band, property of a material or an object whereby sound energy is converted into heat by propagation in a medium or when sound strikes the boundary between two media.

Sound Absorption Related Terms - listed alphabetically

Sound Absorption Coefficient is the fraction of sound energy absorbed by a material. Expressed as a value between 1.0 = perfect absorption (no reflection) and 0 = zero absorption (total reflection). The value varies with frequency and angle of incidence, determined experimentally. Metric unit, sabin per square metre

Sound Absorption Coefficient is also known as the sabine absorption coefficient

Absorption Coefficient - under sound absorption coefficient

Absorption Definition (IEC 702-02-12) conversion of electromagnetic or acoustic wave energy into another form of energy, for instance heat, by interaction with matter.

Absorption Factor, the property of a body that determines the fraction of the incident radiation or sound flux absorbed by the body. Also known as absorptivity

Absorption Loss Definition (IEC 801-23-40) that part of the transmission loss due to the dissipation or conversion of sound energy, either within the medium or attendant upon a reflection.


Atmospheric Sound Absorption over short distances (100 metres) atmospheric sound absorption may be ignored. At greater differences it can be significant particularly at frequencies above 1 kHz and it is temperature and humidity dependent.

Equivalent Sound Absorption Area (A), is the sound absorber or soft furnishings, etc., required to produce the required reverberation time in a room.

Equivalent Absorption Area of an Object or of a Surface Definition (IEC 801-31-06) area of a surface having a sound power absorption coefficient of unity that would absorb the same amount of sound power in a reverberant room with a diffuse sound field as the object or the surface. In the case of a surface, the equivalent absorption area is the product of the area of the surface and its sound power absorption coefficient

Impedance Tube is a method for measuring sound absorption coefficients by means of standing (stationary) waves in a tube, also known as a standing wave tube

Noise Reduction Coefficient (NRC) a single number rating system used to compare the sound absorbing characteristics of building materials. A measurement of the acoustic absorption performance of a material, calculated by averaging its sound absorption coefficients at 250, 500, 1000 and 2000 Hz, expressed to the nearest multiple of 0.05.

Passive Sound Absorbers dissipate sound energy as heat.

Reference Sound Absorption (Ao) when measuring sound insulation between rooms it is common practice to normalize the measured levels to a reference sound absorption of 10 m2

Room Absorption Coefficient is the ratio of Sabine absorption of a surface to the area of the surface, the unit is the sabin.

Room Absorption Definition (IEC 801-31-11) is the sum of sabine absorption due to objects and surfaces in a room, and due to dissipation of sound energy in the medium within the room.

Sabin is a unit of sound absorption
One square metre of 100% sound absorbing material has a value of 1 metric sabin.
One square foot of 100% sound absorbing material has a value of 1 imperial sabin.

Sabine : Wallace Clement Sabine an American pioneer in architectural acoustics. He derived an expression for the duration T of the residual sound to decay below the audible intensity. The associated sound absorption unit was named after him - sabin without the e.

Sabine Absorption Definition (IEC 801-31-10) sound absorption defined by the Sabine reverberation-time equation The unit of Sabine absorption is the decibel metre-squared, sometimes known as the metric sabin.

Sabine Absorption Coefficient Definition (IEC 801-31-12) quotient of Sabine absorption of a surface by the area of the surface. Is also known as the sound absorption coefficient
Note : with αi as the Sabine absorption coefficient of the i-th surface whose area is Si, the Sabine absorption attributed to the surface is Ai = Siαi.

Sabine Reverberation-time Equation under reverberation time

Sound Absorbers for use in buildings are ranked A to E, as specified in BS EN ISO 11654.

Sound Reduction Coefficient under noise reduction coefficient

Standing Wave Tubes also known as impedance tubes are used to measure sound absorption coefficients by means of the standing (stationary) sound waves in a tube.

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