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Reverberation is the persistence of sound after it has ceased as a result of many reflections from surfaces like room walls, furniture, air, etc. within a closed surface.
- Each reflection produces a new reflection, which progressively disappears as the surfaces of the objects in the contained space absorb them.
- Reverberation is the same as echo, except there is less distance between the source and the obstruction through which it is reflected.
- The reverberation time parameter is mostly used in the numerical calculation of reverberation.
- Reverberation time is defined as the amount of time it takes for a sound to drop by around 60 dB from its initial level.
- The time delay in the reverberation process should be less than 0.1 second, which means that the reflected wave should reach the observer in less than 0.1 second.
- The delay between the perception of the sound and the original sound is very short, and the original sound remains in the mind when the reflected sound is heard.
Very Short Answers Questions [1 Mark Questions]
Ques. What is reverberation?
Ans. Reverberation is the effects of the persistence of sound after it has been stopped due to repeated reflections from surfaces such as furniture, people, air, and so on within a closed surface.
Ques. The reverberation of sound is due to
- Multiple diffractions
- Multiple refractions
- Multiple reflections
- Multiple polarizations
Ans. The correct answer is c. Multiple reflections
Explanation: The reverberation of sound is due to the multiple reflections from the surfaces.
Ques. Which of the following does not affect the reverberation time?
- Frequency of sound
- Size of the auditorium
- Area of the walls, ceiling, and floor
- Nature of the walls
Ans. The correct answer is a. Frequency of sound
Explanation: The reverberation time is unaffected by the frequency of the sound. It is only affected by the auditorium's size, the type of wall, and the presence of any significant solid bodies in the surroundings. The frequency is unaffected by the reverberation time.
Ques. In an auditorium or big hall, excessive reverberation is highly _______.
- Zero
- Desirable
- Undesirable
- None of the above
Ans. The correct answer is c. Undesirable
Explanation: The sound emitted in a large hall will be reflected off the walls repeatedly until it is diminished to the point where it is no longer audible. Reverberation refers to the recurrent reflection that results in the persistence of sound. Excessive reverberation is extremely undesirable in an auditorium or large venue.
Ques. Mark the correct statement.
- Rock music also becomes less pleasing with excessive reverberation.
- Excessive reverberation is desirable in the case of orchestral and choral music.
- Excessive reverberation makes the speech of a person indistinct.
- All of the above
Ans. The correct answer is d. All of the above
Explanation: Reverberation is the phenomenon of sound continuing to be heard after it has been stopped due to repeated reflections off surfaces such as furniture, people, air, and so on within a closed surface. However, excessive reverberation is undesirable since the sound created will be heard again while the next sound is sent forth. This is uncomfortable to hear, and the sound is not clear. So, all the statements are correct.
Short Answers Questions [2 Marks Questions]
Ques. What if the reverberation time is too long?
Ans. The reverberation time of a room or hall is defined as the time it takes for the sound to decay by 60 decibels. The reverberation time is 6 seconds if the sound decays from 100 dB to 40 dB in 6 seconds. When the reverberation time is too long, an echo is produced. When the reverberation time is long, we will hear a distinct echo.
Ques. What are some of the advantages of reverberation?
Ans. The sound quality of musical symphonies and orchestra halls is greatly enhanced when there is reverberation present. As a result, sound engineers are hired during the construction of large infrastructure.
Ques. Is reverberation similar to echo?
Ans. The concepts of reverberation and echo are nearly identical. Both are time-based audio effects created by sound reflection off of hard surfaces. Reverberation is the persistence of sound after the sound source has been switched off. And echo is the sound produced by sound waves reflected off the surface back to the listener.
Ques. What are the disadvantages of reverberation?
Ans. Excessive reverberation causes the sound to become distorted. If there are no sound-absorbing surfaces in a space, such as roofs, walls, or floors, sound will bounce back between them. The listener appears unable to assess the speaker in such a setting since he hears both direct and recurrent reflected sound waves.
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Long Answers Questions [3 Marks Questions]
Ques. What can we do to reduce reverberations?
Ans. Reverberation can be reduced by using sound-absorbing material to cover the surfaces of objects inside the enclosed space.
- Porous materials such as mineral wool and fiberglass are used as absorbents.
- Through friction, sound waves penetrate mineral wool and convert sound energy to heat.
- The reflected sound decays significantly faster in this situation, leaving the listener with only the original sound.
Ques. What are the applications of reverberation?
Ans. The following are the applications of reverberation
- Producers of live or recorded music use the phenomena of reverberation to improve sound quality.
- Several technologies for producing and simulating reverberations have been created.
- A Chamber reverberator is one such example, in which the sound is created by a loudspeaker and then picked up by a microphone, along with various reverb effects.
- A plate reverberator is a similar device in which a metal plate creates vibrations instead of a loudspeaker.
Ques. What are the characteristics of reverberation?
Ans. The characteristics of reverberation are
- Many reflections can be caused by the surfaces of objects contained in the room, such as a wall, furniture, or air.
- The appearance of reflections in fewer than 50 milliseconds is referred to as reverberation.
- Reverberation is the persistence of sound after it has been generated.
Very Long Answers Questions [5 Marks Questions]
Ques. What is the difference between Echo and Reverberation?
Ans. The difference between echo and reverberation is
| Echo | Reverberation |
|---|---|
| It is caused by sound reflection from surfaces such as walls, furniture, and other objects. | Multiple reflections of sound waves from surfaces such as walls, furniture, and other objects produce reverberation. |
| A distance of approximately 17 m is necessary between the source and the reflecting body. | The distance between the source and the reflecting surface is quite small in the case of reverberation. |
| It arises regardless of surface and may be heard efficiently in both open and enclosed environments. | It generally occurs in enclosed areas and is more easily heard on closed surfaces. |
| The echo penetrates the ears steadily. | Reverberation causes them to pile up in the ears, making understanding and distinguishing more difficult. |
| It doesn’t cause any irritation or anxiety | Because it is difficult to identify between continuous noises, it irritates. |
Ques. How do we Measure Reverberation?
Ans. A sound level meter and loudspeaker are tools that may be used to measure the reverberation time.
- Additionally, the Sabins formula may be used to determine the reverberation time.
- Moreover, the volume of the room and the overall level of absorption inside a space serve as the foundation of this equation.
- The volume of the room (length, breadth, and height) and the surface materials are used to get the sabin values.
- A chart with the sabins at each octave band frequency for materials used in construction might be helpful.
- Finally, the addition of the sound absorption to the calculation can take place.
Ques. Find reverberation time for a room of dimension 40 x 30 x 20 ft3 having an average absorption coefficient of 0.15.
Ans. Given
- The length of the room, L = 40 ft
- The breadth of the room, B = 30 ft
- The height of the room, H = 20 ft
- Average absorption coefficient, a = 0.15
The volume of the room is given by
V = 40 x 30 x 20 = 24000 ft3
The surface area of the room is given by
S = 2 (LB + BH + LH)
⇒ S = 2(40 x 30 + 30 x 20 + 20 x 40)
⇒ S = 2 x (1200 + 600 + 800) = 5200 ft2
Reverberation time is given by
τ = 0.049V / aS
Where
- V is the volume of the room
- a is the average absorption coefficient
- S is the surface area of the room
On substituting the values, we get
τ = (0.049 x 24000) / (0.15 x 5200)
⇒ τ = 1.51 seconds
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