Acoustic Glossary


Sound Absorption : Definitions, Terms, Units, Measurements..

Sound Absorption IEC Definition,

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


Sound Absorption

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


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


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

Attenuation Coefficient another name for Sound Absorption Coefficient.

Equivalent Sound Absorption Area

the area of a perfect absorber or soft furnishings, etc., required to produce the required reverberation time in a room.

Impedance Tube

a method for measuring Acoustic 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.

Reference Sound Absorption : A0

when measuring sound insulation between rooms it is common practice to normalize the measured levels to a Reference Sound Absorption A0, of 10 m²

Room Absorption

sum of Sabin Absorption due to objects and surfaces in a room, and due to dissipation of energy in the medium within the room.

See also : Reference Sound Absorption above

Room Absorption Coefficient

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


a unit of Sound Absorption of a surface.
A square metre of 100% 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% absorbing material has a value of 1 imperial sabin.

Sabin Absorption 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, not the sabine. Wallace Sabine developed the Formulae

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 absorption unit was named after him - sabin without the e.

Sabine Equation

in 1898 W C Sabine also came up with the formulae relating reverberation time with sound absorption and room volume: T = 0.161 V/A
where :
V = room volume in m3
A = α x S = equivalent absorption surface or area in m2
α = absorbent coefficient or attenuation coefficient
T = RT60 = reverberation time in s, seconds
S = absorbing surface in m2

It follows if you know the reverberation time you can calculate the absorption coefficient and vice-versa.

Sound Absorption Class classification of sound absorbers into Sound Absorption Classes A-E, according to BS EN ISO 11654, including frequencies 200-5000 Hz..

Sound Absorption Coefficient IEC Definition,

quotient of Sabine absorption of a surface by the area of the surface
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.


Sound Absorption Coefficient is also known as Sabine Sound Absorption Coefficient

Sound Absorption Coefficient the fraction of sound energy absorbed by a material. It is 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 - see sabin and Sabine's equation.

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

Sound Absorption Loss IEC Definition,

that part of the transmission loss due to the dissipation or conversion of sound energy, either within the medium or attendant upon a reflection.

Standing Wave Tube a method for measuring Sound Absorption Coefficients by means of the standing waves in a tube.


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