Acoustics_Vocabulary

=//Absorption Class// = =Classification of sound absorbers into Sound Absorption Classes A-E, according to EN ISO 11654, including frequencies 200-5000 Hz. = = = =//Flutter echo// = =Occurs when noise bounces between parallel surfaces in a room. = = = =//Noise Reduction Coefficient (NRC)// = =Single value for sound absorption according to ASTM C 423, derived as the mean value of 4 frequencies in the range 250-2000 Hz. = = = =//Reverberation time, (T or RT)// = =The time it takes for the sound pressure level to fall by 60 dB after the sound has been turned off. Measuring the reverberation time allows us to calculate the total sound absorption. The reverberation time varies according to the frequency. = = = =//Sabine// = =The physicist Wallace Clement Sabine (1869-1919) created in Riverbank, west of Chicago, the well known Sabine formula (T=0,16V/A), showing the relationship between reverberation time (T s), room volume (V m³) and the amount of absorption (A m²). = = = =//Sound absorbers// = =Materials and structures with the ability to take up sound energy and convert it into other forms of energy. They improve room acoustics by removing sound reflections, thus reducing the noise and the reverberation time. = = =  =//Sound absorption// = =Means that sound energy is converted into mechanical vibration energy and/or heat energy. Sound absorption is expressed as the sound absorption coefficient //α// or the sound absorption class (A-E) according to EN ISO 11654 or NRC/SAA according to ASTM C 423. =