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

### 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

**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

### Sound Absorbers

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

See also NRC (Noise Reduction 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.

**Sound Absorption Coefficient** of 1 = 100% sound 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

● 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*

See also Absorption Loss Definition

Absorption Class under Sound Absorption Class

Absorption Coefficient under Sound Absorption Coefficient

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. It is temperature and humidity dependent.

Attenuation Coefficient under

Sound Absorption Coefficient.

### Equivalent Sound Absorption Area

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

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 Absorber** dissipates

sound energy as heat.

### Reference Sound Absorption : A0

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

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

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

### Sabin

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

### Standing Wave Tube

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

See also Reverberation

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