## 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

*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.

**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**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 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.

**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. One 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 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 A

_{i}= S

_{i}α

_{i}.

*Sabine Reverberation-time Equation*under reverberation

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

**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 Definition IEC 801-31-12,** quotient of sabine absorption of a surface by the area of the surface and is also known as the *Sabine 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 A_{i} = S_{i}α_{i}.

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 waves in a tube.