**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

**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.

**Atmospheric Sound Absorption** over short distances (100 metres) *atmospheric sound 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** under 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 sound absorption coefficients by means of standing waves in a tube.

An *Impedance Tube* is 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.

**Sabin** a unit of Sound Absorption. 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.

**Sabine 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*. Wallace Sabine developed the Formulae

**Sabine** : *Wallace Clement Sabine M*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 Coefficient Definition** under Sound Absorption Coefficient Definition

**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 A_{i} = S_{i}α_{i}. 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.

See also : Sound Power Absorption Coefficient and Statistical Sound Power Absorption Coefficient

**Standing Wave Tube** a method for measuring sound absorption coefficients by means of the standing waves in a tube.

A **Standing Wave Tube** is also known as an *Impedance Tube*

See also : Reverberation