Auditorium Acoustical design consideration

2. INTRODUCTION
The auditorium, as a place for listening developed from the classical open-air
theaters.
An auditorium includes any room intended for :An auditorium includes any room intended for :
- listening to music including theaters - churches
- classrooms - meeting halls
The design of various types of auditoriums has become a complex problem,
because in addition to its various, sometimes conflicting, aesthetics,
functional, technical, artistic and economical requirements, an auditorium
often has to accommodate an unprecedentedly large audience.

3. INTRODUCTION ….
• In some ways, even the largest hall is no different from the smaller rooms,
the basic acoustic criteria are the same.
- Must have a low ambient noise level from internal and external sources
- Provide a reasonable level of acoustic gain
- Provide appropriate reverberation time
- Avoid artifacts such as echoes.
• Hearing conditions in any auditorium are
considerably affected by purely architectural
considerations like:
- Shape - Layout of boundary surfaces
- Dimensions - Seating arrangements
- Volume - Audience capacity
Defects:
1. Echo
2. Delayed Reflection
3. Sound Shadow
4. Sound Concentration

4. • Reverberation is an important parameter that helps define the sound
quality of an acoustic space.
• This is especially true in large halls.
• Reverberation time is closely linked to the intended purpose for any room,
and to room volume.
REVERBERATION AND ECHO
• Halls designed for speech have
shorter mean reverberation
times than halls designed for
music performance.
• The recommended mean
reverberation time increases
as a function of room volume.

5. Large enclosed spaces are all potentially subject to the problem of discrete
echoes.
The long path lengths and multiplicity of seating positions near and far from
the sound source can easily create echo problems.
REVERBERATION AND ECHO ….

6. Sound amplification system are used for the following purpose:
• To reinforce the sound level when the sound source is too weak to be heard.
• To provide amplified sound for overflow audience.
• To minimize sound reverberation.
• To provide artificial reverberation in rooms which are too dead for
satisfactory listening.
REINFORCEMENT BY LOUDSPEAKER
satisfactory listening.
• To operate electronic organs, chimes etc.
TYPES OF LOUDSPEAKER SYSTEM
Three principal type of loudspeaker
system are available:
1. The centrally located system with a
single cluster of loudspeakers over a
sound source.
This system gives max. realism as the amplified sound comes from the same
direction as original sound.

7. TYPES OF LOUDSPEAKER SYSTEM ….
2. The distributed system, using a
number of overhead loudspeakers
located throughout the auditorium.
This system should be used when:
• Auditorium height is too low to install central system.
• When majority of listeners do not have an adequate sight line of central• When majority of listeners do not have an adequate sight line of central
loudspeakers.
• When sound has to be provided for overflow audience.
• In large halls.
3. The stereophonic system, with two or more clusters of loudspeakers
around the proscenium opening or the sound source.
Stereophonic system preserves the illusion that, the sound is coming from the
original , unamplified source.

8. PROBLEMS ASSOCIATED WITH LOUDSPEAKER SYSTEM
1. Audience will hear two sounds, arriving at
two time.
This difference should not be more than
1/30 sec.
2. When loudspeaker is placed halfway down2. When loudspeaker is placed halfway down
the a large auditorium.
Audience will hear loudspeaker first and
direct sound as a weak echo.
This problem can be overcome by introducing a delayed mechanism in
loudspeaker system

9. • Speech Intelligibility = Power + Clarity
• POWER is affected by :
- Distance from speaker
- Directional relationship to speaker
- Audience absorption of direct sound
- Reinforcement by reflectors
- Reinforcement by loudspeakers
- Sound shadows
• CLARITY is affected by :
- Delayed reflections : Echos, Near Echos, Reverberation
- Duplication of sound source by loudspeakers
- Ambient Noise
- Intrusive Noise

10. VOLUME
• For unamplified speech, it is often necessary to limit the overall room volume. This is
because a large volume requires more speech power than a small room.
• This volume minimization is contrary to rooms designed for music, where a relatively
large volume is desirable.
• In a face-to-face conversation, an unamplified talker may generate a SPL level of about
65 dB. This level decreases 6 dB for every doubling of distance. Sound is also
attenuated as it travels through the hall because of air absorption.
• To support audible levels, the audience area must be placed as close as possible to the
speaker. This minimizes sound attenuation, provides a more direct sound path, and
also improves visual recognition which improves intelligibility.

11. ROOM SHAPE
• The talker-to-audience distance can be
minimized by carefully considering the
room geometry.
• A rectangular shoebox-type hall, with
NORMAL SURROUND
A rectangular shoebox-type hall, with
the stage across one narrow end, may
be excellent for music where an
audience can be seated farther away
and a greater ratio of reverberant sound
is desirable.
• However, a rectangular geometry is
only suitable for a relatively small
speech hall.

12. ROOM SHAPE
• For greater seating capacity, the side walls should be splayed from the stage.
• Splayed side walls allow greater seating area that is relatively close to the stage.
• The splayed walls can usefully reflect sound energy to the rear of the hall.
• A side-wall splay may range from 30° to 60°, the latter is considered a maximum angle,
given the directionality of speech. Generally, fan-shaped halls are not used for musicgiven the directionality of speech. Generally, fan-shaped halls are not used for music
performance.

13. ABSORPTION
• In small speech halls, the majority of absorption is provided by the
audience, therefore, the room surfaces can be relatively reflective. In larger
halls, where there is greater room volume per seat, relatively greater room
absorption is needed.
• Beneficially, a reflective front stage area provides strong early reflections
that are integrated with the direct sound and enhance it. On the contrary,
strong late reflections and reverberation, such as from rear walls, would
not be integrated and may produce echoes.
• To accommodate this, the stage area and front of the hall are made
reflective and absorption is placed in the seating area and rear of the hall.

14. CEILING
• In many large halls, ceiling reflectors, sometimes called clouds, are used to
direct sound energy from the stage to the seating area.
• Both dimensions of a square reflecting panel should be at least five times
the wavelength of the lowest frequency to be reflected.
• When ceilings are high, care must be taken to ensure that path-length
differences between direct and reflected sound are not too great, anddifferences between direct and reflected sound are not too great, and
particularly should not exceed 20 msec.
• In some cases, clouds are made absorptive, to avoid late reflections.

15. FLOORS
• A sloping (raked) floor allows a more direct angle of
incidence which in turn allows less absorption. Generally,
the slope of an auditorium floor should not be less than 8°.
• The floor of a lecture-demonstration hall might have a 15°
angle of inclination.
• Staggering of seats is also recommended.
WALLSWALLS
• Because of its potential to create undesirable late reflections, the rear wall of a
large hall requires special attention.
• Reflections from the rear wall would create a long path-length difference to a
listener at the front of the hall. This can result in audible echoes, particularly
because of the otherwise low reverberation level.
• A reflective concave rear wall would also undesirably focus sound.
• For these reasons, the rear wall of a large hall is usually absorptive.
• In some cases, when added absorption is undesirable because of decreased
reverberation time, reflective diffusers can be placed on the rear wall.

16. TYPES OF AUDITORIUM
1. FOR SPEECH
- Conference Hall
- Lecture Theatre
- Law Court
2. FOR MUSIC
- Concert Hall- Concert Hall
- Music Practice Room
3. MULTI-PURPOSE
- School Assembly Hall
- Town Hall

17. DESIGN DATA

18. Developed Floor
Slope For
Unobstructed
View

20. AUDITORIUM

21. SECTION
SOUND FROOF DOOR

25. LECTURE HALLLECTURE HALL

26. ARCHITECTURAL DESIGN FOR CONCERT HALL
• The first complexity rests with the
music itself.
• Different styles and culture of music
have different acoustical requirements.
• Perhaps the most difficult aspect of hall• Perhaps the most difficult aspect of hall
design is the ambiguity of the goal
itself.
BALCONY
• A balcony can be used to decrease the distance from the stage to some
seating areas, and to provide good sight lines.

27. BALCONY ….
• Generally, the balcony overhang depth
should be less than twice the height of
the balcony underside.
• Ideally, the depth should not be more
than the height.than the height.
• Deep bal. can create acoustical
shadows in the seats underneath bal.
• In addition, reflecting surfaces on the ceiling and side walls, as well as the
underside of the balcony, should be designed to add as much reflected
sound as possible to the seating areas on the balcony and under it, to
supplement the direct sound from the stage.

28. BALCONY
• The front of a balcony parapet should be designed to avoid reflections that
could affect sound quality in the seating areas in the front of the hall. This
is particularly true when the plan view of the balcony has a concave shape.
CEILING
Ceiling height is usually determined by the overall room volume that is• Ceiling height is usually determined by the overall room volume that is
required.
• Ceiling height should be about one-third to two-thirds of the room width.
The lower ratio is used for large rooms, and the higher ratio is used for
small rooms.
• A ceiling that is too high may result in a room volume that is too large, and
may also create undesirable late reflections.

29. CEILING
• To avoid potential flutter echo, a smooth ceiling should not be parallel to the floor.
• In many halls, the ceiling geometry itself is designed to direct sound to the rear of the
hall, or to diffuse it throughout the hall
• Concave surfaces such as domes, barreled ceilings, and cylindrical arches should be
avoided because of the undesirable sound foci they create.

30. WALL
• The rear wall must avoid any large, unbroken concave geometry.
• Side walls must avoid parallelism. This can be avoided by tilting or splaying
wall surfaces.
• These angles can also be advantageously used to direct reflected sound to
the audience seating area, and to provide diffusion.the audience seating area, and to provide diffusion.
• Any surface that unavoidably introduces concave geometry or an
undesirable angle should be covered with absorptive material.

31. FLOOR
• In halls designed for either music or speech, a sloping (raked) floor is
desirable especially for large halls.
• In halls designed for either music
or speech, a sloping (raked) floor is
desirable especially for large halls.
• A sloping floor improves sight
lines, and also improves fidelity in
the seating area.
• When sitting on a sloping floor, the
listener receives more direct sound than would be available on a flat floor.

32. • A sloping floor is desirable in halls where audience sound absorption must be
minimized.
SECTION OF A HALL WITH A REAR BALCONY AND CONSTANT CLEARANCE. THE
RESULT IS AN INCREASED SLOPE FOR THE ELEVATED BALCONY
FOR SAFETY THE SLOPE
SHOULD NOT EXCEED
ABOUT 35O

33. STANDARDSSTANDARDSSTANDARDSSTANDARDSSTANDARDSSTANDARDSSTANDARDSSTANDARDS

34. VOLUME AND CEILING HEIGHTVOLUME AND CEILING HEIGHTVOLUME AND CEILING HEIGHTVOLUME AND CEILING HEIGHT
VOLUME INFLUENCES BOTH REVERBERANCE AND LOUDNESS. FOR HALLS
OF HIGH CAPACITY, A LOW VOLUME PER SEAT HELPS PRESERVE
ACOUSTICAL ENERGY.

35. RECORDING STUDIO
• Good recording studio?
• Only one ultimate criterion—the acceptability of the sound recorded in it for its
intended audience.
AMBIENT NOISE
• Studio must have low ambient noise levels.• Studio must have low ambient noise levels.
• Many noise and vibration problems can be avoided entirely by choosing a site in a
quiet location.
• The maximum external noise spectrum must be reduced to the background noise
criteria goal within the space by the transmission loss of the walls, windows, and
doors.
• A reinforced concrete building, while providing high transmission-loss partitions, also
efficiently conducts noises throughout via structural paths.
• The HVAC (heating, ventilating, and air-conditioning) system must be designed to
provide the required noise criteria goals.

36. DIRECT AND INDIRECT SOUND
• Sound picked up by a microphone in a studio
consists of both direct and indirect sound.
• Direct sound is observable a short distance
away from the source, but farther away, the
indirect sound dominates.
• Sound picked up by a microphone would, for• Sound picked up by a microphone would, for
the first few milliseconds, be dominated by
the direct component, after which the
indirect sound arrives at the microphone as
reflections from room surfaces.
• Another component of indirect sound results from room resonances.
• Resonances dominate the low frequency region in which wavelengths of the sound are
comparable to room dimensions.
• Indirect sound also depends on the materials of construction, such as doors, windows,
walls, and floors. These too are set into vibration by sound from the source

37. OPTIMAL REVERBERATION TIME
• If the reverberation time is too long, speech syllables and music phrases are masked
and a deterioration of speech intelligibility and music quality results. If reverberation
time is too short, music and speech lose character and suffer in quality, with music
suffering more.
• There is no specific optimum
reverberation time, because many
other factors are involved. e.g. is it
a male or female voice, slow or fast
talker, English or German language,
vocal or instrumental, solo flute or
string ensemble, hard rock or a
waltz?
DIFFUSION
• Diffusion contributes a feeling of spaciousness through the spatial multiplicity of room
reflections and the control of resonances.
• Distributing the absorbing material is a useful means of not only achieving some
diffusion, but increasing the absorbing efficiency as well.

38. ROOM SIZE & SHAPE
The size and shape of a room determines its natural resonances - often
called room modes.
Every rectangular room has three sets of primary modes, with one each for
the length, width, and height.
Generally speaking, larger rooms are better acoustically than smaller rooms.
Another important factor in the design of studios is the ratio between the
length, width and height.length, width and height.
The worst shape is a cube, because all three dimensions resonate at the
same frequencies.
HEIGHT WIDTH LENGTH
1.00 1.14 1.39
1.00 1.28 1.54
1.00 1.60 2.33
Ideal Ratios
RATIO SMALL
STUDIO
MEDIUM
STUDIO
LARGE
STUDIO
HEIGHT (ft.) 1.00 8.00 12.00 16.00
WIDTH (ft.) 1.28 10.24 15.36 20.48
LENGTH (ft.) 1.54 12.32 18.48 24.64
VOLUME (cu.ft.) 1000 3400 8000
Sizes

39. Thanks….