The physicist Wallace Clement Sabine (1869-1919) deduced in Riverbank, West of Chicago, the well-known Sabine reverberation equation(T=0,16*V/A), that show the context between the reverberation (RT), the volume of the room (V m³) and the absorption quantity (A m²).
(image): Sabine's formula
Materials and constructions with the ability to "absorb" sound energy and transform this to another type of energy. Sound absorbers improve the room acoustics by removing sound reflects, which lower the noise level and shortens the reverberation.
Means that sound energy is transformed into mechanical vibration energy and/or thermal energy.
Sound absorption is expressed through the sound absorption coefficient α or the sound absorption classes A-E according to EN ISO 11654 or NRC/SAA according to ASTM C 423.
Sound Absorption class
Classification of sound absorbers in the absorption classes A-E according to the international standard EN ISO 11654 in the frequency range 200-5000 Hz.
The ability of a building to prevent sound energy to pass from one room to another. Sound insulation is measured at different frequencies, normally at 100-3150 Hz. Airborne sound insulation is expressed as a single value Dn,c,w , Rw or R'w.
Impact sound insulation is expressed as a single value Ln,w or L' n,w .
Sound pressure/Sound pressure level (dB)
The variations, that sound waves creates in air, are called sound pressure. The lowest sound pressure level, which you can perceive, is 0 dB and is called the hearing threshold. The highest level, which you can endure, is called the pain threshold and is about 120 dB.
Is measured in dB (deciBel). dB is measured by different frequencies. dB(A) (now also LpA) is a single value, which is used to describe the total volume for al frequencies in a way, that mimics the ear's sensitivity. dB(C) (now also LpC) gives special consideration to low frequencies and reflects better, how a hearing injured person perceives sound.
The speech perception is directly dependent on the level of the background noise, the reverberation, and the type of space. There are different methods of how to measure the speech perception. The most common ones are RASTI, STI and %-Alcons.
Speech Transmission Index (STI)
Similar to the RASTI-method, but it is a more complete kind of measurement of the speech perception by measuring al the octaves in the frequency range 125-8.000 Hz.