When attending an assembly inside the school auditorium, you must have observed how different the orator’s voice appears from the original. Also, the sound produced by the musical instruments during a concert in a closed hall appears very different compared to its original sound. Ever wondered why? The answer to this lies in the concept of reverberation of sound.
Reverberation is the phenomenon of the persistence of sound after it has been stopped due to multiple reflections from surfaces, such as furniture, people, air, etc., within a closed surface. These reflections build up with each reflection and decay gradually as they are absorbed by the surfaces of objects in the enclosed space.
It is the same as the echo, but the distance between the source of the sound and the obstacle through which it gets reflected is less in the case of this reverberation. The quantitative characterization of the reverberation is mainly done by using the parameter called reverberation time. Reverberation time is usually defined as the length of the time when the sound decays by about 60 decibels starting from the initial level. In the process of reverberation, the time delay is said to be not less than 0.1 second, i.e. the reflected form of the wave reaches the observer in more or less than 0.1 seconds. Hence, this delay in the perception of the sound and also the original sound is said to be very less and whereas the original sound will still be in the memory when this reflected sound is heard.
Advantages of Reverberation
Reverberations do wonders when it comes to musical symphonies and orchestra halls. When the right amount of reverberation is present, the sound quality gets enhanced drastically. This is the reason why sound engineers are appointed during the construction of these halls.
Disadvantages of Reverberation
If a room has nearly no sound-absorbing surfaces like walls, roofs, and floors, the sound is said to bounce back between the surfaces, and also it takes a very long time as the sound dies. In such a room, the listener will have difficulty registering the speaker. This is because he tends to hear both direct and reflected sound waves. And also, if these reverberations are more excessive, the sound is said to run together with a mere loss of articulation, becoming muddy and garbled.
Application of reverberation
The phenomenon of reverberation is utilized by the producers of live or recorded music to enhance sound quality. Several systems have been developed to produce and simulate reverberations. A Chamber reverberator is one such example, where the sound is produced by a loudspeaker which is then picked by a microphone along with other effects of the reverb. A similar device is a plate reverberator, where a metal plate produces vibrations instead of a loudspeaker.
How can we reduce reverberations?
From our observation, we can say that if the surface of the objects in the nearby enclosed space is covered with sound-absorbing material, the reflected sound will decay much quicker, and the listener will thus receive only the original sound. Porous materials such as mineral wool and fibreglass are examples of such absorbents. As the sound waves penetrate mineral wool, sound energy gets converted to heat through friction.
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