Unit 3
Q 1 Define Reverberation?
Answer:
Reverberation is the phenomenon of persistence of sound after it has been stopped as a result of 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 space enclosed.
Q 2 What is Echo?
Answer:
As a sound wave reaches the end of its medium, it undergoes certain characteristic behaviours. Whether the end of the medium is marked by a wall, a canyon cliff, or the interface with water, there is likely to be some transmission/refraction, reflection and/or diffraction occurring. Reflection of sound waves off of barriers result in some observable behaviours which you have likely experienced. If you have ever been inside of a large canyon, you have likely observed an echo resulting from the reflection of sound waves off the canyon walls. Suppose you are in a canyon and you give a holler. Shortly after the holler, you would hear the echo of the holler - a faint sound resembling the original sound. This echo results from the reflection of sound off the distant canyon walls and its ultimate return to your ear. If the canyon wall is more than approximately 17 meters away from where you are standing, then the sound wave will take more than 0.1 seconds to reflect and return to you. Since the perception of a sound usually endures in memory for only 0.1 seconds, there will be a small-time delay between the perception of the original sound and the perception of the reflected sound. Thus, we call the perception of the reflected sound wave an echo.
Q 3 What is absorption constant?
Answer:
The sound absorption coefficient is the ratio of absorbed sound intensity in an actual material to the incident sound intensity and can be expressed as
α = Ia / Ii
Where
α = sound absorption coefficient
Ia = sound intensity absorbed (W/m2)
Ii = incident sound intensity (W/m2)
The sound absorption coefficient varies with frequency.
Total Room Sound Absorption
The total sound absorption in a room can be expressed as
A = S1 α1 + S2 α2 + ... + Sn αn
= ∑ Si αi
Where
A = the absorption of the room (m2 Sabine)
Sn = area of the actual surface (m2)
αn = absorption coefficient of the actual surface
Mean Absorption Coefficient
The mean absorption coefficient for the room can be expressed as:
αm = A / S
Where
αm = mean absorption coefficient
S = total surface in the room (m2)
The acoustic characteristics of a room can be calculated with the formulas above, or estimated for typical rooms.
Q 4 What is Sound Foci how it is remedy?
Answer:
Sometimes shape of the hall makes sound waves to concentrate in some particular areas of hall creating a sound of large quality. These spots are called sound foci.
Remedies
This defect can be removed by Geometrical design shapes of the interior faces. Providing highly absorbent materials on critical areas (curved spaces)
Q 5 What is Dead spot How it will be corrected?
Answer:
This defect is the outcome of formation of sound foci. Because of high concentration of reflected sound at sound foci, there is deficiency of related sound at some other points. These spots are known as dead spots where sound intensity is so low that it is insufficient for hearing.
Remedies
This defect can be removed by suitably placing diffusers and reflectors. Right proportions of internal spaces. External noises from vehicles, traffic engines, factories, machines etc. may enter the hall either through the openings or even through walls and other structural elements having improper sound insulation.
This defect can be removed by proper planning of the hall with respect to its surroundings and by proper sound insulation of external walls
Q 6 Explain Sabine’s formula for reverberation time?
Answer:
Sabine equation
Sabine’s reverberation equation was developed in the late 1890s in an empirical fashion. He established a relationship between the RT60 of a room, its volume, and its total absorption (in sabins). This is given by the equation:
.
Where 
is the speed of sound in the room (for 20 degrees Celsius), 
is the volume of the room in m³, 
total surface area of room in m², 
is the average absorption coefficient of room surfaces, and the product 
is the total absorption in sabins.
The total absorption in sabins (and hence reverberation time) generally changes depending on frequency (which is defined by the acoustic properties of the space). The equation does not take into account room shape or losses from the sound travelling through the air (important in larger spaces). Most rooms absorb less sound energy in the lower frequency ranges resulting in longer reverb times at lower frequencies.
Sabine concluded that the reverberation time depends upon the reflectivity of sound from various surfaces available inside the hall. If the reflection is coherent, the reverberation time of the hall will be longer; the sound will take more time to die out.
The reverberation time RT60 and the volume V of the room have great influence on the critical distance dc (conditional equation):
Where critical distance 
is measured in meters, volume 
is measured in m³, and reverberation time 
is measured in seconds.
Q 7 What is Reverberation Time?
Answer:
The reverberant sound in an auditorium dies away with time as the sound energy is absorbed by multiple interactions with the surfaces of the room. In a more reflective room, it will take longer for the sound to die away and the room is said to be 'live'. In a very absorbent room, the sound will die away quickly and the room will be described as acoustically 'dead'. But the time for reverberation to completely die away will depend upon how loud the sound was to begin with, and will also depend upon the acuity of the hearing of the observer. In order to provide a reproducible parameter, a standard reverberation time has been defined as the time for the sound to die away to a level 60 decibels below its original level. The reverberation time can be modelled to permit an approximate calculation
Q 8 What is Noise How it will be corrected?
Answer:
Noise is unwanted sound which masks the satisfactory hearing of speech and music. There are mainly three types of noises that are to be minimized. They are (i) air-borne noise, (ii) structure-borne noise and (iii) internal noise.
Air-Borne Noise
The noise that comes into building through air from distant sources is called air-borne noise. A part of it directly enters the hall through the open windows, doors or other openings while another part enters by transmission through walls and floors.
Remedies
The building may be located on quite sites away from heavy traffic, market places, railway stations, airports etc. They may be shaded from noise by interposing a buffer zone of trees, gardens etc.
Structure-Borne Noise
The noise which comes from impact sources on the structural extents of the building is known- as the structure-borne noise. It is directly transmitted to the building by vibrations in the structure. The common sources of this type of noise are foot-steps, moving of furniture, operating machinery etc.
Remedies
The problem due to machinery and domestic appliances can be overcome by placing vibration isolators between machines and their supports. Cavity walls, compound walls may be used to increase the noise transmission loss.
Internal Noise
Internal noise is the noise produced in the hall or office etc. They are produced by air conditioners, movement of people etc.
Remedies
The walls, floors and ceilings may be provided with enough sound absorbing materials. The gadgets or machinery should be placed on sound absorbent material
Q 9 What are the good condition for acoustics?
Answer:
According to classic acoustics theory there are five requirements which, when met, result in good acoustics:
- Appropriate reverberation time depends on the size of the room. W. Furrer’s recommendations can be used in rooms which are between 200 and 20,000 cubic metres. Unless it concerns a concert hall for classical music, the reverberation time must in so as far as possible be the same throughout the entire frequency range.
- Uniform sound distribution is important in large rooms and halls, where the sound must be able to be heard equally well everywhere. It is important to take sound distribution into account in the architecture. A variation of max. ±5 dB anywhere in the room is an appropriate requirement.
- Appropriate sound level for normal conversation is 60-65 dB, and in a busy street 70-85 dB. In large gatherings, a public address system in a dampened room can be used to ensure an appropriate sound level.
- Appropriate, low background noise is one of the most important acoustic criteria – especially in concert halls and theatres. In a room, the background noise may come from technical installations or ventilation systems.
No echo or flutter echoes must occur for the acoustics to be good. It is easy to prevent echo by installing a little sound-absorbing material on the wall.
Q 10 What is Sound?
Answer:
propagates through an elastic material medium. A purely subjective definition of sound is also possible, as that which is perceived by the ear, but such a definition is not particularly illuminating and is unduly restrictive, for it is useful to speak of sounds that cannot be heard by the human ear, such as those that are produced by dog whistles or by sonar equipment.
Unit 3
Q 1 Define Reverberation?
Answer:
Reverberation is the phenomenon of persistence of sound after it has been stopped as a result of 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 space enclosed.
Q 2 What is Echo?
Answer:
As a sound wave reaches the end of its medium, it undergoes certain characteristic behaviours. Whether the end of the medium is marked by a wall, a canyon cliff, or the interface with water, there is likely to be some transmission/refraction, reflection and/or diffraction occurring. Reflection of sound waves off of barriers result in some observable behaviours which you have likely experienced. If you have ever been inside of a large canyon, you have likely observed an echo resulting from the reflection of sound waves off the canyon walls. Suppose you are in a canyon and you give a holler. Shortly after the holler, you would hear the echo of the holler - a faint sound resembling the original sound. This echo results from the reflection of sound off the distant canyon walls and its ultimate return to your ear. If the canyon wall is more than approximately 17 meters away from where you are standing, then the sound wave will take more than 0.1 seconds to reflect and return to you. Since the perception of a sound usually endures in memory for only 0.1 seconds, there will be a small-time delay between the perception of the original sound and the perception of the reflected sound. Thus, we call the perception of the reflected sound wave an echo.
Q 3 What is absorption constant?
Answer:
The sound absorption coefficient is the ratio of absorbed sound intensity in an actual material to the incident sound intensity and can be expressed as
α = Ia / Ii
Where
α = sound absorption coefficient
Ia = sound intensity absorbed (W/m2)
Ii = incident sound intensity (W/m2)
The sound absorption coefficient varies with frequency.
Total Room Sound Absorption
The total sound absorption in a room can be expressed as
A = S1 α1 + S2 α2 + ... + Sn αn
= ∑ Si αi
Where
A = the absorption of the room (m2 Sabine)
Sn = area of the actual surface (m2)
αn = absorption coefficient of the actual surface
Mean Absorption Coefficient
The mean absorption coefficient for the room can be expressed as:
αm = A / S
Where
αm = mean absorption coefficient
S = total surface in the room (m2)
The acoustic characteristics of a room can be calculated with the formulas above, or estimated for typical rooms.
Q 4 What is Sound Foci how it is remedy?
Answer:
Sometimes shape of the hall makes sound waves to concentrate in some particular areas of hall creating a sound of large quality. These spots are called sound foci.
Remedies
This defect can be removed by Geometrical design shapes of the interior faces. Providing highly absorbent materials on critical areas (curved spaces)
Q 5 What is Dead spot How it will be corrected?
Answer:
This defect is the outcome of formation of sound foci. Because of high concentration of reflected sound at sound foci, there is deficiency of related sound at some other points. These spots are known as dead spots where sound intensity is so low that it is insufficient for hearing.
Remedies
This defect can be removed by suitably placing diffusers and reflectors. Right proportions of internal spaces. External noises from vehicles, traffic engines, factories, machines etc. may enter the hall either through the openings or even through walls and other structural elements having improper sound insulation.
This defect can be removed by proper planning of the hall with respect to its surroundings and by proper sound insulation of external walls
Q 6 Explain Sabine’s formula for reverberation time?
Answer:
Sabine equation
Sabine’s reverberation equation was developed in the late 1890s in an empirical fashion. He established a relationship between the RT60 of a room, its volume, and its total absorption (in sabins). This is given by the equation:
.
Where 
is the speed of sound in the room (for 20 degrees Celsius), 
is the volume of the room in m³, 
total surface area of room in m², 
is the average absorption coefficient of room surfaces, and the product 
is the total absorption in sabins.
The total absorption in sabins (and hence reverberation time) generally changes depending on frequency (which is defined by the acoustic properties of the space). The equation does not take into account room shape or losses from the sound travelling through the air (important in larger spaces). Most rooms absorb less sound energy in the lower frequency ranges resulting in longer reverb times at lower frequencies.
Sabine concluded that the reverberation time depends upon the reflectivity of sound from various surfaces available inside the hall. If the reflection is coherent, the reverberation time of the hall will be longer; the sound will take more time to die out.
The reverberation time RT60 and the volume V of the room have great influence on the critical distance dc (conditional equation):
Where critical distance 
is measured in meters, volume 
is measured in m³, and reverberation time 
is measured in seconds.
Q 7 What is Reverberation Time?
Answer:
The reverberant sound in an auditorium dies away with time as the sound energy is absorbed by multiple interactions with the surfaces of the room. In a more reflective room, it will take longer for the sound to die away and the room is said to be 'live'. In a very absorbent room, the sound will die away quickly and the room will be described as acoustically 'dead'. But the time for reverberation to completely die away will depend upon how loud the sound was to begin with, and will also depend upon the acuity of the hearing of the observer. In order to provide a reproducible parameter, a standard reverberation time has been defined as the time for the sound to die away to a level 60 decibels below its original level. The reverberation time can be modelled to permit an approximate calculation
Q 8 What is Noise How it will be corrected?
Answer:
Noise is unwanted sound which masks the satisfactory hearing of speech and music. There are mainly three types of noises that are to be minimized. They are (i) air-borne noise, (ii) structure-borne noise and (iii) internal noise.
Air-Borne Noise
The noise that comes into building through air from distant sources is called air-borne noise. A part of it directly enters the hall through the open windows, doors or other openings while another part enters by transmission through walls and floors.
Remedies
The building may be located on quite sites away from heavy traffic, market places, railway stations, airports etc. They may be shaded from noise by interposing a buffer zone of trees, gardens etc.
Structure-Borne Noise
The noise which comes from impact sources on the structural extents of the building is known- as the structure-borne noise. It is directly transmitted to the building by vibrations in the structure. The common sources of this type of noise are foot-steps, moving of furniture, operating machinery etc.
Remedies
The problem due to machinery and domestic appliances can be overcome by placing vibration isolators between machines and their supports. Cavity walls, compound walls may be used to increase the noise transmission loss.
Internal Noise
Internal noise is the noise produced in the hall or office etc. They are produced by air conditioners, movement of people etc.
Remedies
The walls, floors and ceilings may be provided with enough sound absorbing materials. The gadgets or machinery should be placed on sound absorbent material
Q 9 What are the good condition for acoustics?
Answer:
According to classic acoustics theory there are five requirements which, when met, result in good acoustics:
- Appropriate reverberation time depends on the size of the room. W. Furrer’s recommendations can be used in rooms which are between 200 and 20,000 cubic metres. Unless it concerns a concert hall for classical music, the reverberation time must in so as far as possible be the same throughout the entire frequency range.
- Uniform sound distribution is important in large rooms and halls, where the sound must be able to be heard equally well everywhere. It is important to take sound distribution into account in the architecture. A variation of max. ±5 dB anywhere in the room is an appropriate requirement.
- Appropriate sound level for normal conversation is 60-65 dB, and in a busy street 70-85 dB. In large gatherings, a public address system in a dampened room can be used to ensure an appropriate sound level.
- Appropriate, low background noise is one of the most important acoustic criteria – especially in concert halls and theatres. In a room, the background noise may come from technical installations or ventilation systems.
No echo or flutter echoes must occur for the acoustics to be good. It is easy to prevent echo by installing a little sound-absorbing material on the wall.
Q 10 What is Sound?
Answer:
propagates through an elastic material medium. A purely subjective definition of sound is also possible, as that which is perceived by the ear, but such a definition is not particularly illuminating and is unduly restrictive, for it is useful to speak of sounds that cannot be heard by the human ear, such as those that are produced by dog whistles or by sonar equipment.
