The document discusses acoustics in auditoriums. It defines acoustics and sound, and discusses topics like sound frequency and intensity, reflection of sound, defects due to reflected sound like echoes and reverberation, Sabine's equation for calculating reverberation time, absorbent materials used in auditoriums, acoustic design considerations for auditoriums including volume, shape, seating, and defects that can occur. It also covers noise mapping and sound insulation. The overall goal is to provide guidelines for designing auditoriums with good acoustics.

1. ACOUSTICS OF AUDITORIUMS
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2. 1 . INTRODUCTION
• Acoustics is defined as the science of sound as it deals
with origin, propagation and sensation of sound
• Sound is produced when a part of atmosphere is
compressed suddenly. Sound cannot travel in vacuum
• Unpleasant sound is called noise
• Mainly deals with reflected sound
• Here , the word auditorium means the places where
quality of sound is very important
• Ex : musical halls , seminar halls etc…
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3. 2 . SOUND
2.1 FREQUENCY AND INTENSITY
• Frequency is no. of pressure variations in unit time
• Intensity is flow of sound energy through unit area per time
• If I1 andI2 are intensities and they differ by n bels ,
𝑛 = log10
𝐼1
𝐼2
𝑚 𝑑𝑏 = 10 log10
𝐼1
𝐼2
The difference in loudness m is known as intensity level.
• Unit of phon indicates the level of sounds of equal loudness at
all frequencies
• The threshold of hearing is zero and that of painful hearing is
130 db
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4. 2.2 REFLECTION OF
• Laws of reflection
of light are
applicable
• Above assumption
is not applicable in
certain
circumstances and
great care should be
taken there
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SOUND

5. • Concave surfaces lead to concentration of reflected waves
at certain points. So they are used as reflectors.
Convex surfaces spread out the waves and hence they are
used to spread the sound throughout the room.
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6. 2.3 DEFECTS DUE TO REFLECTED SOUND
1. ECHOES:
When reflected sound waves reach ear just when the
original sound has already been reached, an echo is produced.
• The sensation of sound persists for
1
10
th of a second
after the source has been stopped
• If the distance of reflecting surface <17m , distorted sound
will be heard
• If a no. of reflecting surfaces are provided , multiple echoes
are formed. Ex: heavy rolling sound of thunder
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7. 2. REVERBERATION
• Some time is needed for sound to transform to other form of
energy. This is brought about by friction b/w sound waves and air
particles as well as the surfaces against which it strikes. This
gradual process needs specific time known as reverberation time
𝑚 = 10 log10
𝐼1
𝐼2
For an average speaker ,
𝐼1
𝐼2
= 106 so that 𝑚 = 60 𝑑𝑏.
• Thus time of reverberation time is the time required by sound to
decay to one-millionth of its initial value
• Reverberation time 𝛼 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑜𝑜𝑚
𝛼
1
𝑎𝑟𝑒𝑎 𝑜𝑓 ℎ𝑜𝑙𝑒𝑠 𝑖𝑛 𝑟𝑜𝑜𝑚
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8. Optimum reverberation time for halls
TYPE OF HALL REVERBERATION FACTOR AUDIENCE
Churches 1.8-3 Two-thirds
Cinema theatres 1.3 Two-thirds
Music halls 1.6-2 Full
Parliament houses 1-1.5 Quorum
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9. 3. SABINʼS EQUATION
𝑡 =
0.16𝑉
𝐴
where t is reverberation time in seconds
V is volume in 𝑚3
𝐴 = (𝑎1𝑠1 + 𝑎2𝑠2 + ⋯)
=total absorbing power in 𝑚2- sabins .
• The unit of sound absorption (𝑚2
-sabin ) is equal to sound
absorption of one metre square area of fully open window
• If room has no holes , then A physically represents effective
area of room , as it behaves like a hole
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10. 4. ABSORBENT MATERIALS
Materials incorporated on the surfaces of room for better
acoustics are called Absorbent materials. Important facts
about them are:
• They should be water-proof and fire-proof
• They are soft and porous
• Their absorbing capacity depends on the thickness and
density of material and frequency of sound
• Acoustic properties can be changed by their modes of fixing
• In a big hall, audience is a major absorbing factor
• Improper covering destroys the absorbent properties of
materials
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11. 4.1 ABSORBENT MATERIALS
1. Hairfelt
2. Acoustic plaster
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12. 3. Acoustical tiles 4. Pulp boards
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13. 5. Compressed fibre board 6. Perforated ply wood
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14. 7. Wood wool board
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15. 5. ACOUSTIC DESIGN 0FAUDITORIUMS
1. Volume :
• The volume should be large enough such that music spreads
over the hall
• Halls of small volume are used for weak sounds
• The floor area calculated is 0.60 to 0.90 𝑚2
/person
• Average height varies between 6 m and 7.5 m
2. Site Selection :
• Mostly based on noise pollution
• If no air-conditioning is provided , orientation should be such that
external noise is limited to minimum
• Background noise level should not increase 45 𝑑𝑏
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16. 3. Sound absorption :
• The surface which reflects sound should be designed to assist
sound distribution
• Rear walls , balcony and concave surfaces should be provided
with absorbent materials
4. Shape :
• Convex walls are preferred over concave ones
• A fan shaped floor plan gives better performance due to
favourable reflection from sides
• For synchronisation of lip movement with sound, the distance of
farthest seat from curtain line should not exceed 23 m
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17. Shapes for auditorium
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18. Fan shaped plan of auditorium
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19. 5.Seats and seating arrangement
• The seats should be
arranged in concentric
arcs of circles
• Seats should be
provided in staggered
position
• The back to back
distance between two
rows must be at least
450 mm and maximum
limit is 1000 mm
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20. Seating arrangement in auditorium
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21. 6. Balcony seats
• They should not be
inclined more than 300.
• If covered seats are
provided, acoustics
characteristics are not
changed considerably
• If balconies are deep ,
sound shadows may
develop
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22. 7. Raising and width of seats
• The successive rows
should be raised over
preceeding ones
• The rise in level varies
between 80 mm to 120
mm per row
• The width of seats
should be between 400
to 600 mm
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23. 5.2 DEFECTS IN AN AUDITORIUM
1. Reverberation :
• The effect of excessive reverberation is that sound once
produced prolongs for a longer duration
• The remedy is to correct time of reverberation by
installing absorbing materials
2. Loudness :
• This is due to the lack of reflecting surfaces near the
source and excessive absorption of sound in the hall
• The remedy is to provide hard reflecting surfaces near
source of sound. If length is more , more than 1 loud
speaker must be provided
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24. 3. Sound foci :
• In concave surfaces ,
reflected waves meet at
certain spots and create
sound of large intensity
4. Dead spots :
• Because of sound foci,
there is deficiency of
reflected sound at some
points
• This can be avoided by
providing diffusers
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25. 6. NOISE MAPPING
The procedure for making a
noise map or topograph is as
follows:
1. An accurate sketch
showing relative position
of all objects are drawn
2. The noise levels are
marked on suitable
number of positions
3. The connecting times
between points of equal
sound levels are drawn
and a noise map is
obtained
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26. 7. SOUND INSULATION
• Reduction in the level of sound when it passes through a
building component
• Hard materials are good sound insulators
• The insulation of sound is measured in adjoining room
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OVERALL INSULATION SITUATION OF ROOMS
30 Between rooms in one house
40 Between houses,between wards in
a hospital
45 Between extra quiet wards in a
hospital
50 Between living rooms in a flat

27. 8. CONCLUSION
• In order to attain better sound control in a room,
usually we go for acoustic materials
• We have to take each room for separate case study
and design it based on the situation prevailing
and experience of the engineer
• Sound absorption mainly deals with control of
reflected sound whereas sound proofing is
purposefully stopping the passage of sound
between two rooms
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28. 9. REFERENCES
1. E.G.Richardson (1957), Acoustics for Architects,
Edward Arnold (Publishers) Ltd. London
2. Fritz Ingersler (1952), Acoustics in Modern Building
Practice, The Architectural Press London
3. L.Cremer and H.A.Muller (1982), Principles and
Applications of Room Acoustics, Applied Science
4. L.Nijs and Diemer de Vries (2004), The Young
Architectʼs Guide to Room Acoustics, Acoustical
Science and Technology
5. M.Barron (1993), Auditorium acoustics and
Architectural design, E & FN Spon, London
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29. 6. P.Lord and D.Templeton (1986), The
Architecture of Sound; Designing Places of
Assembly, The Architectural Press, London.
7. Rangwala (2013), Building Construction,
Charotar Publishing House Pvt. Ltd. India.
8. Vern.O.Kundsen and Cyril.M.Harris (1950),
Acoustical Designing in Architecture,
Chapman and Hall, Ltd. London
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30. THANK YOU
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31. Any doubt????
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