Sound Absorption Terms, Definitions, Units, Measurements
, sound energy
is 'absorbed', to some extent, by the different media
that sound waves
encounter, along their transmission path, from the source to the receiver.
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 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 is also known as the sabine absorption coefficient
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
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.
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.
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 Coefficient
is the ratio of Sabine absorption
of a surface to the area of the surface.
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
. 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 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 Ai
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