Acoustic terms beginning with A
Absorption Coefficient (a)
Frequency dependent coefficients commonly used to describe the fraction of acoustic energy absorbed at a boundary.
A value of 1.0 indicates all energy is absorbed and there will be no resultant reflection from this surface. A value of 0 indicates no energy is absorbed. These limiting values are theoretical, and in practice some energy will always be absorbed / reflected.
NOTE: Measured a values are often quoted as being greater than 1. This is a result of the measurement technique and not actually achievable. 1.0 is actually the practical limit.
Airborne Sound
Term used to describe sound sources that originate from within free space or a room, which may then propagate into the structure. Used to differentiate from structureborne sound.
See also:
Sound
Attenuation
General term for the reduction in amplitude, magnitude or intensity of a physical quantity, in this case, acoustic energy. This is generally a result of absorption, scattering or dispersion within a medium, although this latter parameter is often not considered a form of attenuation.
A-Weighting
An A-weighting network is used to reflect the differential sensitivity of human hearing
to sounds of different frequency. I.e. it is a set of correction terms applied to sounds of different frequency measured using absolute 'linear' sound measurements (dB(lin)).
The A-weighting sound pressure level, LpA, is measured on a scale defined by the dB(A).
Environmental Acoustics / Noise
Noise sources from road, rail, aeroplanes, industry and entertainment facilities all count as sources of environmental noise. Rated according to their own international (ISO) and national (BS) standards, it is an area of acoustics that is taken very seriously.
To monitor and assess environmental noise, complex systems of monitoring and prediction are used to interpret existing scenarios as well as the likely change / increase due to development and expansion, and their likely environmental impact on local communities.
Commonly used descriptors for defining environmental noise are the LAeq,T,L90,T, and L10,T. The LAeq,T is defined as "the value of the A-weighted sound pressure level of a continuous, steady sound that, within a specified time interval T, has the same mean square sound pressure as a sound under consideration whose level varies with time."
The L90,T is a measure of the level of sound exceeded over 90 percent of a period of time, T.
Similarly with L10,T this is the level exceeded 10 percent of a period of time.
Recent projects include:
Guru Nanak Sikh VA Secondary School (pictured, below)
Langley Grammer School, Slough
Stamford Endowed Schools, Lincs
Kendrick School, Reading
Guru Nanak Sikh VA Secondary School
Transmission, Absorption and Reflection
Three terms used for describing the resultant distribution of acoustic energy impinging on a boundary such as a wall partition.
Transmission describes the acoustic energy that passes through the partition.
Absorption is the mechanical conversion of energy into heat as the sound wave does 'work' on the partition. This is the energy that is lost by the sound wave upon interaction with the interface. With the case of absorption panels situated on a surface, the deeper the absorption material, the more it will attenuate low frequencies - this is evident in comparison of the absorption coefficients for our absorption panels - the depth of the panel becomes more and more comparable to the wavelength of the low frequency sound waves leading to greater mechanical interaction.
Reflection describes the acoustic energy that is deflected by the object.
In summary:
Incident sound energy = Transmitted + Absorbed + Reflected energy