Reverberation
Introduction
Reverberation is a sound phenomenon produced by reflection "Reflection (sound)"), which consists of a slight permanence of sound once the original source has stopped emitting it.
When we receive a sound, it comes to us from its transmitter through two channels: the direct sound and the sound that has been reflected by an obstacle, such as the walls of the room. When the reflected sound is intelligible by humans as a second sound, it is called an echo, but when, due to the form of the reflection or the phenomenon of acoustic persistence, it is perceived as an addition that modifies the original sound, it is called reverberation.
Reverberation, by modifying the original sounds, is a parameter that significantly quantifies the acoustics of a room. To assess its intervention in the acoustics of a room, the "reverberation time" is used. The effect of reverberation is more noticeable in large, poorly absorbing rooms and less noticeable in small, highly absorbing rooms.
Theoretical description
Reverberation is the acoustic phenomenon of reflection that occurs in a room when a wave front or direct field hits the walls, floor and ceiling of the room.[1] The set of these reflections constitutes what is called reverberant field. The parameter that allows quantifying the degree of reverberation in a room is the so-called Reverberation time (TR), being the period of time in seconds that elapses from when the direct field exciter source is deactivated until the sound pressure level has decreased by 60 dB with respect to its initial value. The theoretical determination of the TR allows this indicator to be related to the dimensional and absorption parameters of any room. The best known and most used expression is Wallace Clement Sabine's formula.
In addition to the total time, a reverb is characterized by the time of first reflection, which corresponds to how long it takes for the sound to reach the listener after reflecting off the nearest wall. The time of the first reflection characterizes the apparent size of the room, from an acoustic point of view.
The so-called “reverb color” is an important factor in the sound quality of a room. Differences in color or timbre are due to the different absorption factors of the wall, ceiling and floor covering materials, for different frequencies. "Clear" or "bright" reverberations occur in rooms lined with materials that better reflect the high-pitched region of the frequency spectrum. If the sound reflected by these surfaces is rich in sounds from the lower part of the spectrum, the reverberation is "dull" or "dark." In both cases, if the effect is very pronounced, the intelligibility of the spoken word is impaired, since speech understanding depends on the medium frequencies. The only type of room that does not alter the spectrum of sounds heard inside is the anechoic room, which does not present any type of reverberation because all the surfaces that delimit it are completely absorbent.