Acoustic Glossary


 

Sound Absorption and related terms, definitions, units etc.,


Sound Absorption

sound energy is absorbed by 'acoustically soft' materials that sound waves encounter, as opposed to being reflected by 'acoustically hard' materials.

An open window is an example of 100% sound absorption i.e. no reflection, whereas bathrooms have 'hard' reflective surfaces and therefore very low sound absorption properties and the result is multiple reflections 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.

IEC 801-31-01, property possessed by materials and objects of converting sound energy to heat either by propagation in a medium or when sound strikes the boundary between two media

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, i.e. zero absorption (total reflection). The value varies with frequency and angle of incidence, determined experimentally - see Sabin and Sabine's equation.

A Sound Absorption Coefficient of 1 = 100% absorption - for example an open window.

Sound Absorption Coefficient Definition.

IEC 801-31-12, quotient of sabine absorption of a surface by the area of the surface. Also known as the Sabine 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.


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 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.

Anechoic


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.

Attenuation Coefficient under Sound Absorption Coefficient.

Equivalent Sound Absorption Area

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 саsе 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 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 acoustical 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

is the sum of sabin absorption due to objects and surfaces in a room, and due to dissipation of sound energy in the medium within the room.
 

Room Absorption Coefficient

is the ratio of sabine absorption of a surface to the area of the surface.

Sabin

is a unit of sound absorption. A square metre of 100% sound absorbing material has a value of 1 metric sabin. An example of this would be a 1 m² open window. 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

is defined by the Sabine reverberation time equation. In a reverberant room of volume V, speed of sound c, and decay rate d, the sabin absorption is A = 0.921 Vd / c : the unit is the sabin. Wallace Sabine developed the Formulae

Sabine Absorption Coefficient Definition under Sound Absorption Coefficient

Sabine Reverberation Equation under Reverberation


Sound Absorbers

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

See also • NRC (Noise Reduction Coefficient)


Standing Wave Tubes

also known as Impedance Tubes are used to measure sound absorption coefficients by means of the standing waves in a tube.

See also • Reverberation

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