## Sound Absorption Terms and Definitions .....

**Sound Absorption**, sound energy is 'absorbed' by the different media that sound waves encounter, along their transmission path, from the source to the receiver.

**Sound Absorption Definition** (IEC 801-31-12) 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.

An open window is an example of **100% sound absorption** i.e. no reflection, whereas bathrooms usually have sound reflective surfaces and therefore very low **sound absorption** properties, resulting in multiple reflections in the room 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 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.

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 absorption coefficient* is also known as the sabine absorption coefficient

Sound Absorption 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 Factor**, the property of a body that determines the fraction of the incident radiation or sound flux absorbed by the body. Also known as **absorptivity**

**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.

**Equivalent Sound Absorption Area (A),** 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 case 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 (stationary) 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 acoustic 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 normalise the measured levels to a **reference sound absorption of 10 m ^{2}**

**Room Absorption Coefficient** is the ratio of Sabine absorption of a surface to the area of the surface, the unit is the sabin.

**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.

**Sabin is a unit of sound absorption**

One square metre of 100% sound absorbing material has a value of

**1 metric sabin**.

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.

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 absorption coefficient* is also known as the sound absorption coefficient

**Sabine Reverberation-time Equation**under reverberation time

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

**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 (stationary) sound waves in a tube.