Auditorium Acoustics

Auditorium Acoustical design consideration

2. INTRODUCTION The auditorium, as a place for listening
developed fromthe 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 fromthe
smaller rooms
,
the
basic acoustic criteria are the same
.
- Must have a
low ambient noise level
frominternal and external sources
- Provide a
reasonable level of acoustic gain
- Provide appropriate
reverberation time
-
Avoid
artifacts such as
echoes
.
•Hearing conditions in any auditoriumare
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 purposefor any room,
and to roomvolume.
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 roomvolume.

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 systemare 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
systemare 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 fromthe 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 systemshould be used when:
•
Auditoriumheight 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 prosceniumopening or the sound source.
Stereophonic systempreserves the illusion that, the sound is coming fromthe
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
down
2.
When
loudspeaker
is
placed
halfway
down
the a large auditorium.
Audience will hear loudspeaker first and
direct sound as a weak echo.
This problemcan be overcome by introducing a
delayed mechanismin
loudspeaker system

9. •Speech Intelligibility = Power + Clarity
•POWER is affected by :
- Distance fromspeaker
- 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
roomgeometry.
•
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
fromthe 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 from30°to 60°, the latter is considered a maximumangle,
given
the
directionality
of
speech
.
Generally,
fan
-
shaped
halls
are
not
used
for
music
given
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 roomsurfaces can be relatively reflective. In
larger
halls
, where there is greater roomvolume 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
fromrear 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
fromthe 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,
and
differences
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 auditoriumfloor
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.
WALLS WALLS •Because of its potential to create undesirable late reflections, the
rear wall
of a
large hall
requires special attention
.
•Reflections fromthe 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 focussound.
•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 HALL LECTURE 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 fromthe 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 fromthe 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 roomwidth
.
The lower ratio is used for large rooms, and the higher ratio isused for
small rooms.
•A ceiling that is too high may result in a roomvolume 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 oran
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 35
O

33. STANDARDS STANDARDS STANDARDS STANDARDS STANDARDS STANDARDS STANDARDS STANDARDS

34. VOLUME AND CEILING HEIGHT VOLUME AND CEILING HEIGHT VOLUME AND CEILING HEIGHT VOLUME 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 maximumexternal noise spectrummust be reduced to the background noise
criteria goal within the space by the transmission loss of thewalls, 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) systemmust 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 fromthe 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 fromroomsurfaces.
•Another component of indirect sound results fromroomresonances.
•Resonances dominate the low frequency region in which wavelengths of the sound are
comparable to roomdimensions.
•Indirect sound also depends on the materials of construction, such as doors, windows,
walls, and floors. These too are set into vibration by sound fromthe 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 inquality, 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 roomdetermines its natural resonances - often
called
roommodes.
Every rectangular roomhas 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 ratiobetween 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….