The phenomenon of sound build-up – sometimes in rooms, one can observe the phenomenon of increasing energy of acoustic waves after the sound source initiates its emission. In acoustic terminology, this is called the aftersound. The occurrence of this phenomenon is closely related to a large number of reflected sound waves from barriers in the room. After-sound is the time that elapses from the initiation of sound by the source until the sound reaches its maximum intensity as a result of build-up. Multiple reflections of sound from the walls of the room can significantly enhance its energy.
In some cases, the phenomenon of sound build-up is generated intentionally. However, it can also lead to undesirable phenomena, including echo. The effect of sound build-up is only noticeable when there is a time gap of more than 50 milliseconds between the arrival of the direct wave to the human ear and the arrival of the reflected acoustic wave.
Proper acoustic arrangement of the room and the use of acoustic devices can positively influence the reduction of the phenomenon of sound build-up.
The opposite of after-sound in acoustics is reverberation.
