A
Absorption
Acoustical absorption is the energy transformation from acoustic energy pressure waves) to thermal energy in a porous material like mineral wool.
Absorption Coefficient α
The absorption coefficient α is a material property, which describes how well a material absorbs sound waves... α=1 means 100% absorption, α=0 means 100% reflection.
When building materials for inner boarding are chosen, the function of the room and the absorption coefficient of the boarding must be harmonized.
A high absorption coefficient is not necessarily a good one – it depends on the function of the individual room. The absorption coefficient has an impact on reverberation time.
A measure of the sound-absorbing ability of a surface. It is defined as the fraction of incident sound energy absorbed or otherwise not reflected by a surface. Unless otherwise specified, a diffuse sound field is assumed. The values at the sound-absorption coefficient usually range from about 0.01 for marble slate to almost 1.0 for long absorbing wedges often used in anechoic rooms.
The sound absorption coefficient can be measured in 1/3 octave bands according to ISO 354 and weighted as αw acc. to ISO 11654.
Acoustic impedance
The acoustic impedance Z (or sound impedance) is the ratio of sound pressure p to particle velocity v in a medium or acoustic component and is usually represented in complex notation as Z=R + iX. The real and imaginary components are called, respectively, acoustic resistance and acoustic reactance.
See also characteristic impedance.
Airflow resistance
See specific airflow resistance.
Airflow resistivity
See specific airflow resistance.
Air absorption
Air absorption is usually neglected in calculations of reverberation times for auditoriums, but for large enclosures it may become signifi cant. Air absorption is greater for high frequencies and is dependent upon air temperature and relative humidity.
In calculations of reverberation times the air absorption can be included by adding an equivalent absorption area for the sound attenuation by air as (acc. to EN 12354-6):
Aair=4*m *V
V - room volume
