MODULE 3 – ACOUSTICAL DESIGN

• 5). Acoustical Design of Auditoriums – Multipurpose Halls : History of Greek,

Roman theaters, Use of IS code 2526 – 1963 for design and detailing of Auditoriums –
Cinema Halls – Multi-purpose Halls – Halls for speech and music.
• 6) Acoustical Design and Detailing of other spaces - Open air theaters, Halls for
indoor sports, home theaters, recording studios, open plan offices, etc. Need and use of
sound reinforcement systems, sound masking systems and speech privacy.
5). MULTIPURPOSE HALLS : HISTORY OFF GREEK AND ROMAN THEATERS.
• The theater derived from the Greek word was initially place for seeing than hearing.
• The spectators stood on the hill side and watched the action (usually dancing) which
took place on the cleared place or stage on the foot hill.
• Later this was developed into circular area called orchestra with two third area
covered by rows of benches around it.
• Afterwards platform was added behind orchestra (Skene)
• All action took place on circular orchestra whereas skene was used as utility, rest and
recreational purpose only by actors.
• Further skene was developed into LOGEION which was elevated form of stage used in
Roman theaters.
• Greeks realized that the power of an average voice is inadequate to provide distinct
hearing in the distant part of a large open air theater hence actors used large masks
not only to emphasize characters but to enhance or reinforce the power of voice
(megaphone effect).
EARLY FORM OF GREEK THEATER WITH SEPARATE SKENE BEHIND
ORCHESTRA
GREEK THEATERS
ROMAN THEATERS
• It was usually located on the plane area outside city.
• It was the single unit i.e. Auditorium, orchestra and stage all
connected together.
• Auditorium and orchestra were reduced to semi circular shape
with semi circular benches.
• Skene became a large platform (LOGEION) well elevated enclosed
by side and rear reflective walls.
• The walls decorated with relief work and there were three large
doorways in the rear wall and one on the either side.
EARLY ROMAN THEATER WITH LOGEION AND SEMI CIRCULAR
ORCHESTRA

2 3 4
ROMAN THEATERS
 THEATER AT ORANGE
In the Roman theatre the orchestra is a place to sit, instead of a performing area as the
Greeks had used it. The stage grows in importance and is brought into direct contact with the
audience. The auditorium is a semicircle, often partially supported by a hill underneath as well
as concrete vaulting. Corridors under the tiers were used in case of rain. This is the best-
preserved Roman theatre.
• The Roman amphitheatre was the centre of entertainment in Rome, Ruins of
amphitheaters
can be found all over the empire.
• The largest amphitheatre in the empire was the CoIosseum,
• Rome which could seat up to 50,000 people.
• The amphitheatre was the place where people went to see fights.
• These fights were between slaves, prisoners of war or criminals, and sometimes wild
animals.(bull fighting)
• These fights were so popular that schools were set up to train ordinary men as special
fighters known as Gladiators.
THE ROMAN THEATRE IN ORANGE(50 AD)
ANCIENT ROMAN THEATERS & AMPHITHEATER
 COMPARISION

GREEK THEATER ROMAN THEATER

Use of I.S. Code 2526-1963---DESIGNING AND DETAILING OF AUDITORIUMS.
• Selection of site in a quiet surroundings.
• Noise survey to determine the extent of sound insulation requirements and
construction.
• Arrangements of rooms within the building for controlling noise, including solid and
air borne noise.
• Shape and size that will ensure proper diffusion of sound in all parts of room for
speech, drama and music.
• Proper selection and distribution of absorptive and reflective material and
construction that will provide optimum conditions for the growth decay and steady
distribution of sound.
• Proper installation of sound amplification system.

DETERMINING THE AUDITORIUM FLOOR AREA

• The required floor area of an auditorium can be calculated by multiplying the intended
number of seats by about eight square feet then adding the required aisle space and
the desired stage area.
• Once the required floor area has been calculated, the shape and layout of the
auditorium should be determined by acoustic requirements and the calculation of
sight lines. Of course, there may be some architectural and engineering controls on
the available shape caused by site constraints or certain construction methods, but
these need to be addressed along with the acoustic parameters.
WORKING ON THE AUDITORIUM
VOLUME
Some of the most basic auditorium design parameters have a significant effect on the
acoustic environment, which is why they must be discussed in the earliest design stage. The
ratio of the length to width for a typical auditorium should be between 1.2 and 1.7.(i.e. If
width is 1 then length could be 1.2---1.7) Even more important is the ratio of auditorium
height to width, which should be between 0.4 and 0.7.
EXAMPLE
1:1.5:0.5=100’X150’X50’
If the ceiling is too low, it restricts
1:1.5:0.5= 70’X1o5’X35’
stage sound from reaching the
people at the rear of the room. If
too high, sound reflected from
the ceiling arrives much later
than the initial direct sound from
the stage and affects intelligibility.
Actual ratios should be an
acoustically informed decision
based on required seating,
auditorium dimensions, shape,
layout and internal angles.
VOLUME PER SEAT

•The optimum vol./seat for a room is the lowest value consistent with the visual and
aesthetic requirements with the comfort of the audience and with regard to
appearance.
 
•MOTION PICTURE ------- 1000 CAPACITY -------- 125 CFT/SEAT
•EXAMPLE: 50’X70’X35’---ie. IN THERATIO OF 1:1.4:0.7

2000 CAPACITY -------- 175 CFT/SEAT

•MUSIC ROOMS------------- 1500 CAPACITY -------- 100 CFT/SEAT
 
•Lower vol./seat will reduce the cost of maintenance, air conditioning, cleaning,
lighting, redecorating etc.
 
•If the seats, carpets, draperies etc. have been carefully chosen there may be no need
for additional acoustical material to control reverberation. Further lower the
vol./seat, the higher will the sound level in the room for a source of a given power.
BEST CONCERT HALL IN THE WORLD
• One example of an acoustically sound auditorium is the Concertgebouw in
Amsterdam, with a length to width to height ratio of 1.5 : 1 : 0.63. Built in 1888,
critics still consider it one of the best concert halls in the world. The ceiling in the
2,200-seat auditorium is 58 feet high.
• i.e. 116’ wide, 174’legth and 58’high.

PROBLEM

In both Greek and Roman open air theaters actors were frequently disturbed by the
converging reflectors – since action took place on the stage which was located on the
centre of curvature with elevated rows of seats.
SOLUTION
Forms other than circular should be adopted for the theater including the seating
arrangements.
Or centre of curvature to be shifted to convenient place.
Risers inclined slightly backward to ten degrees to reflect sound upwards.
Risers retaining walls etc. to be covered with shrubs, plants and bushes for absorption.
 PLANNING THE AUDITORIUM
1. Examine the site with respect to noise
(tolerable noise level is 30 to 40 db )
2. Limit the size of the auditorium
3. Design the shape (ref. to sketches in the next slide)
4. Provide optimum R.T. in all parts of the auditorium.
THE AUDITORIUM'S PLAN SHAPE
• Of these, the most solid choices are fans, rectangles and modified polygons; square is acceptable if
the auditorium is large enough; while cruciform and round shapes are the hardest to design for
good acoustics. After all, the cruciform is actually four rooms joined together in the form of a cross,
so sound from each section affects hearing in other sections. The problem with round or partially
round rooms is that the walls will reflect the sound waves to focus on a particular point. This is
similar to the way a semicircular reflector in a flashlight focuses light rays into a narrow beam. At the
beginning, architect must resist the temptation to depart from acoustically tried and tested shapes
in search of something unique that runs the risk of favoring form over function.
DESIGN OF A ROOM

•  Floor plan:
The seating should be arranged as near to the stage as possible taking into account
distribution of sound and visibility. Ratio of length to width is between 2:1 and 1.2: have
been found satisfactory. Circular or elliptically shaped floor plans give rise to focusing effects
and non-uniform distribution of sound and echoes. In order to bring audience as close as
possible to the stage and auditorium –floor plan should be designed with diverging side
walls. If path length is 65’ or more between direct and reflected sound it gives rise to
echoes---and between 50’ and 60’ produce blurring quality of sound resulting in lack of
intimacy .
• It is very important to use floor area which has the best acoustical environment for
SEATING and POOREST areas for non listening purposes (aisles)
ELEVATION OF SEATS (RAKING OF SEATS)
•  Elevate the seats in order to provide a free flow of direct sound from source to the listeners
– since sound waves which graze audience are greatly attenuated as audience contribute
highly absorptive surface. The first few rows can be level—since they have a good line for
both sight and sound. The higher the source is elevated farther back level can be extended.
• An angle of elevation should not less than 8 degrees. In a demonstration lecture hall it
should be at least 15 degrees. Steeper elevation is desirable without making aisles too
steep.
AUDITORIUM, KONGU ENGINEERING COLLEGE COIMBATORE,
INDIA
AUDITORIUM, KONGU ENGINEERING COLLEGE COIMBATORE,
INDIA
AUDITORIUM, KONGU ENGINEERING COLLEGE COIMBATORE,
INDIA
AUDITORIUM, KONGU ENGINEERING
COLLEGECOIMBATORE, INDIA
CEILING
• The ceiling should provide favorable reflections of sound and also aid in diffusion of
sound .
• If adequate means of diffusion are furnished by the floor and wall surfaces then the
ceiling may be utilized for reflection of sound.
• Ceiling height used for music and speech should be about – 1/3 rd or 2/3rd of width of
the room –lower ratio for large halls and higher for small rooms. E.g. for auditorium of
size 100’ x 150’ – a ceiling ht. of 30’ to 35’ is adequate whereas for a room size of 18’ x 24’
ht. of 10’ to 12’ is optimum.
• The ceiling should provide favorable reflections of sound and also aid in diffusion of sound
.
• If adequate means of diffusion are furnished by the floor and wall surfaces then the
ceiling may be utilized for reflection of sound.
• Ceiling height used for music and speech should be about – 1/3 rd or 2/3rd of width of
the room –lower ratio for large halls and higher for small rooms. E.g. for auditorium of
size 100’ x 150’ – a ceiling ht. of 30’ to 35’ is adequate whereas for a room size of 18’ x 24’
ht. of 10’ to 12’ is optimum.
THE AUDITORIUM'S INTERNAL GEOMETRY

SOUND REFLECTED FROM INCLINED REAR WALL

 THE LITTLE THEATER : ( 300 capacity)
 
• For 300 capacity vol. should not exceed 50,000 cft. All seats are located on one floor. Steep
slope to have good line of sight and sound in all parts of the auditorium. The lower 6’to 8’ of
the side walls should be of reflective material.(wainscoting)
• The rear wall should not be concave. It should be treated with highly abs. material and
deeply inset doors, hangings and ornaments which will reduce effect of long delayed
reflections and help in diffusing the sound. For additional acoustical treatment to achieve
required R.T. upper portion of side walls may be treated with non uniform strips or panels.
The chairs should be upholstered. Stage with rear, side and over head surfaces should be
treated with reflective plywood. The stage should be well elevated (42”) above the front
floor level and orchestra pit should be avoided. Optimum R.T. is 1.5 sec at 125 cycles and
1.00 at 500 & 4000 cycles for speech and music. Noise level of 30 to 35 db is acceptable.
• The auditorium is isolated by two side walls adj. to streets in combination with
promenades, lobby which provides approx. T.L. of 60 dbs. If the site is located nearby road
and air traffic it is advisable to treat these enclosed spaces with highly abs. material or
even double wall construction.  
• The aisles to be covered with carpet to reduce the noise of foot falls and the floor
underneath the seats with marblex or lenoleum to reduce the noise of scuffing of feet. 
• Small set of reflectors made of pressed fiber board or plywood placed forward on stage will
project the sound towards auditorium. 
 THE LITTLE THEATER : ( 300 capacity)
• The auditorium is isolated by two side walls adj. to streets in combination with
promenades, lobby which provides approx. T.L. of 60 dbs. If the site is located nearby
road and air traffic it is advisable to treat these enclosed spaces with highly abs.
material or even double wall construction.  
• The aisles to be covered with carpet to reduce the noise of foot falls and the floor
underneath the seats with marblex or lenoleum to reduce the noise of scuffing of feet. 
• Small set of reflectors made of pressed fiber board or plywood placed forward on stage
will project the sound towards auditorium. 
• If all the above precautions are taken the intelligibility of speech , drama, music will be
excellent.
BALCONY RECESS
• Good design of a balcony recess requires a shallow depth and a high opening.
Depth should not extend twice the ht. of the opening. In large auditoriums and
theaters it is advisable to break up the rear wall in order to provide proper
diffusion in the recess.
• Balcony wall should never be overlooked since it is quite large. By tilting this
surface downwards it is possible to utilize the resulting reflections to increase the
sound level in the middle and rear portion of auditorium. 
• The balcony soffit and rear wall should be designed so that large portion of sound
coming directly from the source will be reflected towards audiences under the
balcony and remainder absorbed by rear wall.
  THE LEGITIMATE THEATER (large theater)
• Most of the principles are same as little theater. The only difference is that speech is at lower
level than in the little theater because of its larger size. Hence it is important to design the
shape of the auditorium to provide audience with greatest possible amount of direct and
beneficially reflected sound. The divergence of the side walls, the slope of the overhead
proscenium splay, and the slope of the main ceiling of the auditorium should be carefully
designed to reinforce the sound propagated to the audience, and some preferential
reflection of sound should be provided for the rear seats under and in the balcony. 
• Balcony overhang should be less than the twice the ht. of the balcony opening and to keep
the balcony soffit reflective and inclined downward toward the rear wall.  
• Heavily upholstered chairs, carpets on the aisles and abs. treatment of rear wall will prevent
objectionable reflections. It is important that stage have the same R.T. as the auditorium.
SIDE WALLS
• The side walls reflecting the sound are beneficial to those seats where sound is
inadequate by providing splays. But in large auditorium if these reflected sounds are
delayed echoes may be created, in such cases the side walls should be treated with
rough surface to diffuse the sound or treated with absorptive material. Flutter echoes
usually occur between side walls which can be avoided by diverging non parallel or
tilted walls or splayed walls.
MOTION PICTURE THEATERS
Concave rear walls, parallel side walls, parallel ceiling and floor, and surfaces that give long
delayed reflections in the seating area must be avoided.
 
Because the sound is produced by means of electro-acoustical equipment , the acoustical
design of a cinema is not completely dependent on beneficial reflections from walls,
proscenium, splays, and ceilings as in legitimate theater. The ave. sound level of speech is
65 db. for dialogue and a capacity of 1000 seats should have an amplifier of at least 20
watts.

Lengths greater than 150’ should be avoided. (1/7 second) since it will create lack of
synchronism between sight and the sound. The floor should rise steeply towards the rear,
the loudspeakers and screen should be well elevated. Splays and other functional
deviations in the wall and ceiling contours can be used to give proper diffusion of sound.
 MOTION PICTURE THEATERS

• A relatively deeper overhang of balcony can be tolerated since the ave. speech level is
somewhat higher. The balcony soffit should slope downward toward rear and should
not be absorptive. Vol ./seat ---- 125 to 150 cft is good but lower vol. is still better. By
this building cost is reduced, load on A.C.is reduced, (smaller units both for A.C. &
sound amplification system)
• Treatment of the walls behind the screen with highly abs. material prevents sound
radiating from the back of the loudspeakers from being reflected to the audience.
• Since the projection booth is potential source of noise , it should be treated with
fireproof acoustical material. Doors and windows must be made sound proof.
 
 A CASE STUDY OF A MULTI-PURPOSE HALL
• The acoustical characteristics of hall depend primarily on the size --volume, capacity, shape of
the various surfaces type of upholstery employed gradient of the floor, design of the stage
and other materials used.
• The acoustic of multipurpose hall spaces require considerable thought in arriving at optimal
acoustics. More specifically Reverberation quality of the hall is important.
• A case study of the hall with a capacity of 766 . From the history of the hall it has been
gathered that a large number of seminars, meeting and cultural programmes have been
conducted. They are found to be successful.
PLAN OF TAPOVAN HALL AT CHENNAI

• The study of Acoustical characteristics of a hall either before or after construction are very
important. A case study describing the architectural features of a multipurpose hall which is
used for lectures ,musical performances ,and other cultural events has been chosen.
• The acoustical characteristics of a hall depend on cubic volume, interior shape, density of
materials and on surfaces and size, spacing and number of the chairs, carpets or other sound
absorbing materials. The acoustical quantity that can be measured fundamentally is the
reverberation time (Ref tables).The auditorium has seating capacity of 766.
• A fully air conditioned auditorium rated as one of the best auditoriums with excellent
acoustics and spacious seating arrangements. Several cultural, educational and social
organizations in and around Chennai patronize the hall to conduct seminars, meetings and
cultural programs.
PLAN OF TAPOVAN HALL AT CHENNAI
PLAN OF TAPOVAN HALL AT CHENNAI
ARCHITECTURAL FEATURES
• The auditorium is fan shaped, the main hall is 533 sq.m and the stage is 267sq.m. A fully air
conditioned auditorium with spacious seating arrangements, ensuring comfortable access to
seats inside the auditorium without causing inconvenience to other occupants.

• The upper ceiling is circular plan in the center with sound reflecting panels. The side walls
are treated with fiber wool and the flooring is treated with wood. The balcony is accessed
through the first floor with two main doors. With sufficiently large foyer in the front and
spacious verandas on both sides of the auditorium.

ACOUSTICAL MATERIALS
Ceiling: Plaster over concrete planks.
Walls: Treated with fiber wool materials.
Carpets: On aisles of main hall and balcony directly affixed to concrete.
Stage side walls: Wooden planking about1mm thick from the stage floor up to height 10m.
Stage floor: Wood.
Stage height: 0.75m
Seating: Backrest is 12cm thick molded plywood. Top of seat bottom and front of backrest
are upholstered, porous fabric over open cell foam. Armrests are wooden.
Optimum Reverberation time measurements have been made in the
hall (unoccupied) at different locations; using the instrument Nor sonic
Sound Level Meter (Nor 132).

• R.T. TABLE
• LOCATION RT VALUES (sec)
250 500 1000 2000 4000 8000
• 1. 1.11 1.99 1.80 1.99 1.90 1.72

• 2 1.51 1.61 1.69 1.68 1.73 1.53

• 3 1.35 1.99 1.85 1.11 1.02 0.81
• 4 1.68 1.23 0.93 0.99 0.87 0.67
• 5 1.08 1.67 1.61 1.69 1.525 1.39
• 6 1.52 1.66 0.94 1 0.94 0.6
 ACOUSTICAL DESIGN RECOMMENDATIONS
• HALLS FOR SPEECH AND MUSIC
• Selection of site in a quiet surroundings.
• Noise survey to determine the extent of sound insulation requirements and construction.
• Arrangements of rooms within the building for controlling noise, including solid and air
borne noise.
• Shape and size that will ensure proper diffusion of sound in all parts of room for speech and
music.
• Proper selection and distribution of absorptive and reflective material and construction that
will provide optimum conditions for the growth decay and steady distribution of sound.
• Proper installation of sound amplification system.
• All noises whether of outside or inside origin should be reduced to levels that will not
interfere with hearing of speech and music.
• The hall’s shape and size should be designed to give proper diffusion to the sound. It should
reinforce the sound especially towards rear seating area balancing favorable ratio of direct
and indirect sound. For this purpose it is necessary to design a special wall and ceiling
surfaces to act as reflectors and some times introduction of splays or irregular surfaces to
provide proper diffusion of sound.
• Provision should be made for reinforcing the music and speech in all parts the room. For a
big hall in addition to the reflective surfaces a high quality sound amplification system is
indispensable.
• All noises whether of outside or inside origin should be reduced to levels that will not
interfere with hearing of speech and music.
• The hall’s shape and size should be designed to give proper diffusion to the sound. It should
reinforce the sound especially towards rear seating area balancing favorable ratio of direct
and indirect sound. For this purpose it is necessary to design a special wall and ceiling
surfaces to act as reflectors and some times introduction of splays or irregular surfaces to
provide proper diffusion of sound.
• Provision should be made for reinforcing the music and speech in all parts the room. For a
big hall in addition to the reflective surfaces a high quality sound amplification system is
indispensable.
• Freedom from disturbing noise (about 40 db) sufficient sound level (60 db) for the audience,
proper shape (usually same for both music and speech) and optimum reverberation
conditions provide satisfactory acoustic conditions in the hall. Reverberation enhances the
tones produced by a musical instrument.
• Room intended for speaking purposes should provide good “ intelligibility of speech ”
• In the design of music rooms the prime objective is the enrichment of the tonal quality and
blending of the sounds.
6) Acoustical Design and Detailing of other spaces
• Open air theaters, Halls for indoor sports, home theaters, recording studios,
open plan offices, etc. Need and use of sound reinforcement systems, sound
masking systems and speech privacy.
THE DESIGN OF OPEN – AIR THEATER
The design of open-air theatre should include:
1. Selection of site
2. Orchestra shell
3. Sound amplification system.
4. SELECTION OF SITE: Quietness is most important. It should be away from traffic
both on ground and in the air. It should be covered on all sides by natural
slopes of surrounding hills, by artificial embankments, and by a dense growth
of trees. It should be free from winds. Noise survey should be conducted to
know max and min. noise levels which in any case should not exceed 40 db.
The slope of seating area should be 12 degrees. A seating capacity of 600
should be regarded as the upper limit for theater size when there is no sound
amplification system . This corresponds to max. depth of 75 feet and max.
width of 85 feet.
ORCHESTRA SHELL
It increases the average sound level throughout the auditorium and provides a more uniform
distribution of sound pressure over the entire seating area. It also enables the performers to
hear each other more clearly. The simplest type of orchestra shell has highly reflective vertical
wall behind the stage. Sound will be almost equally reinforced in all directions in front of the
wall and to all parts of the audience. The stage floor should be well elevated and the auditorium
floor should be sloped up towards rear to permissible limits. The addition of vertical side walls to
the shell will reinforce the sound further. They should be non parallel with splays or convex
surfaces incorporated which will diffuse the sound throughout seating area. (useful when sound
amplification systems are used). An overhead inclined reflector is a valuable addition to a
vertical wall behind the stage.
SPEECH ARTICULATION TEST
These are employed as a measure of how well speech can be heard in the open air in order to
determine the limiting dimensions of open-air theatres. If a speaker calls out 1000
meaningless speech sounds and an observer hears 850 of them correctly, the speech
articulation is said to be 85% (85%= very good, 75%= satisfactory, 65%=not acceptable). These
tests indicate that an open – Air Theater should be located in a site which is free from winds. If
such a site cannot be found then the theater should at least be so oriented that wind will blow
from stage toward the audience.
OPEN-AIR THETER WITH ORCHESTRA SHELL
OPEN AIR THEATER ORCHESTRA SHELL
OVER ALL VIEW OF ORCHESTRA SHELL AND OPEN AIR
THEATER
ACOUSTICS OF INDOOR SPORTS HALLS AND GYMNASIA
• Investigate the acoustic environment in schools. It includes acoustic and noise surveys of a
wide range of teaching spaces in both unoccupied and occupied conditions; questionnaire
surveys of students and
• Teachers; and testing of student performance in different noise conditions.
• As a result they have a dramatically different acoustic environment.
• It is also known that sports teachers are exposed to high noise levels and
• experience significantly more voice problems than teachers of other subjects.
• For indoor sports noise level of 40 dbs and R.T. of 1.5 seconds are accepted.
HOME THEATERS
• When clients meet experts to discuss building a custom home theater room in their house,
they usually focus on details like the screen size, the surround sound system, the theater
seating, or the popcorn machine. While all of these things are important, none of them are
as important as room acoustics.
• Movies are recorded so that the audience hears noises all around, which makes you feel like
you are a part of the movie. That is why you have multiple speakers in a surround-sound
system:
• Each speaker in a surround-sound system is assigned different sounds.
• A room may look like a theater, but if you can’t comfortably sit down and immerse yourself in
a film for hours -- if you can’t pick up on the subtle emotional qualities in the actors voices
while at the same time fully appreciating action scene, you’re not really getting the
experience you’re looking for.
• A theater that has addressed any acoustical issues enables the movies to be far more
involving. They draw you in, and you connect to them in an entirely different way. That is
what a great home theater experience is all about; escaping from the stress of our work lives
and immersing yourself in another world for a couple of hours. It’s great therapy!
• Achieving this kind of great sound really comes down to two primary things: A well thought
out speaker plan for your room. Making sure the acoustic design of your room enhances the
experience instead of totally destroying the sound your great speakers are reproducing.
 SELECTION OF ROOM
• The Room--Most likely, you know where you'll locate your set-up. It might be the main living
area, a spare bedroom or a basement with a popcorn machine.
• While each of these spaces has special considerations in terms of comfort and sound quality,
there are many common factors.
• Room shape--Square rooms tend to produce odd harmonic distortions. If you have the
choice, opt for a rectangular room, and plan to place your display screen and main speakers
along a short wall for best sound projection.
• Windows. The fewer, the better. They're hard surfaces that reflect sound-causing audio
distortion, and they admit light that can produce reflections on your viewing surface.

WHY ROOM ACOUSTICS MATERS

• Acoustics is All About Minimizing Reflections.
• As the low bass tone from your speakers or subwoofer(s) bounce around the room, those
tones will build up in certain areas of the room and cause two problems. Some low tones will
be totally canceled out by the reflections, yet other tones will get more pronounced and
overwhelm other frequencies.
• Room Dimensions If you are lucky enough to be building your home theater room from
scratch or have some flexibility in the room dimensions, having a more rectangular shaped
room is best.
• If your room is like many family rooms we see in modern homes, you may have many
openings and it will be pretty far from a standard rectangle.
 ACOUSTICAL TREATMENT
• Heavy curtains and shades help, but that means closing blinds or drapes every time you turn
on your home theater system.
• Walls.-- Regular drywall is a decent surface appropriate for home theater walls. However,
break up large flat surfaces with furniture or drapes. Don't add framed art with glass — it's
too reflective of sound and light.
• Basement---Concrete or concrete block is simply a no-no. If you're setting up in a basement
with concrete walls install acoustic wall panels designed specifically for home theaters.
These panels are called "sound absorption" panels, and they help modulate low and high
frequencies, preventing echoes.
• TVs and Blue-Ray with 3-D technology is fast becoming the latest must-have audio-visual
treat. 3-D got a tremendous boost in consumer acceptance from the big-screen movie Avatar.
Already, 3-D television broadcast channels from ESPN, Discovery and Direct TV are a reality.
Those 3-D images look best on big screens.

• Flooring.-- Wall-to-wall carpet, absorbs ambient sound and contributes to coziness.

• Wall/room color.-- Paint your walls as dark as you can tolerate them. Bright colors reflect light
which is distracting.
 SPEAKER PLACEMENT
• A typical home theater features 5.1 surround sound, meaning there are five full-range
speakers and one low-range woofer.
• You'll place three speakers and the woofer toward the front of the room, and the two
remaining speakers on either side and slightly behind your viewing position.
• Keep speakers at least 20 inches from walls. Let's not forget that each room is unique, and
the best sound for you may come only after experimenting with speaker placement.
Fortunately, speakers are moveable.
• In a perfect world, your ears would be equidistant from each speaker. Some speakers —
certainly woofer — will have individual volume controls.
• More sophisticated speakers provide millisecond adjustments, called delays, that time sound
projection from each speaker so that everything arrives in your ears at precisely the same
instant, a handy feature for large rooms with speakers at various distances.
• Of all your speakers, your center front speaker is perhaps the most influential. It bears the
responsibility of projecting sound directly from the screen. This is especially important for
dialogue — you don't want to see the actors talking in front of you while the sound of their
voices is coming from the side.
• Spend time adjusting your center speaker so that dialogue seems to come directly from your
display. Your woofer goes up front, but there's only one, so you have to decide which side.
• Ideal viewing angle can be expressed simply as distance, too, usually 1.5 to 2.5 times the
diagonal width of your screen. That means you should sit no closer than 7.5 feet from a 60-
inch-wide TV, and no more than 12.5 feet away.
 TWEETER AND WOOFER

• In-wall and ceiling models are fine for surround speakers since most of the music and
almost all of the dialogue in a movie comes from the front speakers, with the surround
speakers used mainly for sound effects.

• Most home theater speaker systems are either 5.1 or 7.1 channels. The five main speakers
in a 5.1 system are the front left, center and right (LCR) and the two back surround speakers.
The ".1" is the subwoofer, which produces the deep bass.  A 7.1 system adds two rear
surround speakers.

• A tweeter is for high-frequency sounds and woofers are for low-frequency sounds.

• A tweeter ranges from 200 to 20,000 hertz, which is the upper limit of human hearing. The
name comes from the high-pitched noise that birds make.

• A woofer is usually the largest cone inside the speaker. Subwoofers range from 10 to 120
hertz.  The name comes from the sound of a dog's "woof.
RECORDING STUDIOS
• Achieving ideal studio acoustics is probably one of the most complicated subjects.
• The reason for this is that there are so many different points to consider, such as: Room size
and shape, need for sound isolation, dual purpose rooms requiring variable acoustics.
• Recording multiple performers at once can improve the feel of the music. Sometimes other
instruments will be overdubbed later, so during the initial tracking session they can record
direct using virtual amplifiers and headphones.
PIB (PORTABLE ISOLATION BOOTH)
• Have some movable panels on
hand! Having some movable
panels in a recording room is
incredibly useful.
• Having a number of real
acoustic panels on hand also
opens up a wider variety of
microphone techniques.
PLANNING
• The first thing anyone setting up a recording space
should do – especially if it’s a small, household sized
room – is find a primary “sweet spot” for recording.
• This is where most instruments being recorded will
be set up, or where primary instruments will be if
you are recording more than one performer. In
today’s music, the first question is usually whether
or not you will be recording drums. Drums take up a
lot of space, so in most cases they are the first
consideration when it comes to placement.
• We can plan the entire room setup around the
drums, and have them occupy the center of the
main Sweet Spot.
OPEN PLAN OFFICES
• Direct Speech Paths vs. Reflective Speech Paths
• Open office plans allow for direct speech paths, meaning speech will travel directly from the
speaker to the listener. These paths may be blocked with the introduction of screens. Screens
can be anything that blocks the sound’s path including acoustical products, furniture and
cubicle walls.
• Enclosed plans allow for speech intrusion through shared walls and doors, flanking, and sound
leaks (cracks) in the building’s structure. These paths may be closed by sealing sound leaks,
installing carpeting and softer furnishings, and installing acoustic panels to walls and ceilings.

ACHIEVING BETTER SPEECH PRIVACY IN TODAY’S MODERN OPEN OFFICE

ENVIRONMENT
• Speech privacy is achieved when speech can not be understood.
• This effectively means that in a meeting room, someone listening from outside would know
there was a conversation but would not be able to understand what was being
communicated. In an open plan area, speech privacy is less practical, however reducing the
distance that a conversation can be understood is a practical goal. With sound masking the
radius in which speech can be understood is greatly reduced by raising the background noise
level therefore reducing the speech to noise ratio.
OPEN OFFICE ACOUSTICS
• Attention to office acoustics at the building planning stage will obviously produce the best
results, and it is at this stage that the acoustic specification for each area should be
determined. The acoustician’s objective must be to create an environment which will allow
communication within individual work areas, while minimising distractions and providing
speech privacy in adjacent work areas for open plan areas and to provide speech privacy for
cellular offices but still retaining a flexible partitioning system because of the rate of churn in
today’s business environment.
• The direct speech path might be blocked by a acoustic screen or it could be office furniture.
Workstation orientation is also important, and benefits will be attained by arranging the
layout so that staff do not face each other. The larger the screen or sound barrier, the more
effective it becomes in blocking the direct speech path; however, the open plan concept
usually restricts the number and size of screens which are acceptable. With cellular offices
the screen is already there in the form of the walls.
• The reflected speech paths can be minimised in a number of ways. Soft furnishings will help
significantly, but acoustic wall panels will be much more effective. Lightweight panels can be
fixed to reflective walls or columns, and their fabric facings matched to the office decor
scheme, enhancing the visual aspect of the office in addition to improving its acoustic
characteristics. Doors should have acoustic seals fitted to all four sides. Ceiling systems with
higher absorption coefficients should be installed. Carpets can also make a significant
contribution.
SOUND REINFORCEMENT SYSTEMS
• A sound reinforcement system is the combination of microphones, signal processors,
amplifiers, and loudspeakers in enclosures all controlled by a mixing that makes live or pre-
recorded sounds louder and may also distribute those sounds to a larger or more distant
audience.
• In many situations, a sound reinforcement system is also used to enhance or alter the sound
of the sources on the stage, typically by using electronic effects, such as reverberation, as
opposed to simply amplifying the sources unaltered.
• A sound reinforcement system(SR) for a rock concert in a stadium may be very complex,
including hundreds of microphones, complex live sound mixing and signal processing
systems, tens of thousands of watts of amplifier power, and multiple loudspeaker arrays, all
overseen by a team of audio engineers and technicians.
• On the other hand, a sound reinforcement system can be as simple as a small public address
(PA) system, consisting of a single microphone connected to a 100 watt amplified loudspeaker
for a singer-guitarist playing in a small coffeehouse.
• In both cases, these systems reinforce sound to make it louder or distribute it to a wider
audience.
• A basic sound reinforcement system in a small music venue for the audience are to the left
and right of the stage.
• The main loudspeakers consists of microphones, which convert sound energy such as a
person singing into an electric signal, signal processors which alter the signal characteristics
which produce a powerful version of the resulting signal which convert the signal back into
sound energy .
WHAT IS SOUND MASKING IN NOISE?
• White Noise and Pink Noise---The technique to address privacy issues in the open plan and
closed office environments and reduce noise pollution is called sound masking, which uses a
mix of "white noise" and "pink noise". 
• In sound masking, a precise electronic sound generator, providing shaped "noise", is fed to
an amplifier that supplies an array of specialised wide-dispersion loudspeakers. 
• White noise is a sound that contains equal energy at every frequency.   Like a spinning colour
wheel where all the colours of the visual spectrum will appear white when perceived
together, so “White” noise was superficially similar as an idea for describing audio. To most
people, white noise sounds high-pitched, but this is because the number of frequencies
(hertz) doubles with each rising octave. The energy is there for the lower frequencies, but for
example: there are 100 frequencies between 100Hz and 200Hz,doubling to 200 frequencies
in the next octave, between 200Hz and 400Hz .
PINK NOISE
• Pink noise is a filtered sound that contains equal energy in every octave, compensating for
the increasing quantity of different Hz levels. “Pink” has been said to refer to “human
friendly” noise, as many early sound engineers had a pink complexion and experienced
sound in octaves, using pink to differentiate from the existing type of “White” noise. Pink
noise contains no distracting variations or patterns and may be likened to the sound of soft
airflow.
• Loudspeaker units to be spaced out, providing a uniform volume level over the whole
covered area No high or low spots where the system may call attention to itself The overall
volume to be calculated by analysing the ambient noise present in the area and set to
become part of the normal working environment - typically between 40-45dB
• Absorb and attenuate noise by using high performance acoustic ceilings Block sound with
effective furniture systems (such as dividers)Cover intruding noise with sound masking.
WHITE NOISE
• Rain in Forest White Noise | Sleep, Study, Soothe a Baby | Rain falls in the forest, creating a
soothing white noise to help you sleep, study or soothe a baby.
• The nature sound relaxes the mind while blocking out extraneous noise, so that you can
enjoy a peaceful moment to yourself.
• The rainstorm sound is 10 hours long, so that it can play all night while you sleep. And if you
use it for studying or soothing a baby, the 10 hours ensures that your concentration won't be
broken or that your baby won't be woken up by the white noise stopping.
• White noise is a type of noise that is produced by combining sounds of all different
frequencies together. If you took all of the imaginable tones that a human can hear and
combined them together, you would have white noise. The adjective "white" is used to
describe this type of noise because of the way white light works. White light is light that is
made up of all of the different colors (frequencies) of light combined together (a prism or a
rainbow separates white light back into its component colors).
• In the same way, white noise is a combination of all of the different frequencies of sound.
You can think of white noise as 20,000 tones all playing at the same time.
• Because white noise contains all frequencies, it is frequently used to mask other sounds.
• If you are in a hotel and voices from the room next-door are leaking into your room, you
might turn on a fan to drown out the voices. The fan produces a good approximation of white
noise. Why does that work? Why does white noise drown out voices? Let's say two people
are talking at the same time. Your brain can normally "pick out" one of the two voices and
actually listen to it and understand it. If three people are talking simultaneously, your brain
can probably still pick out one voice.
• However, if 1,000 people are talking simultaneously, there is no way that your brain can pick
out one voice. It turns out that 1,000 people talking together sounds a lot like white noise. So
when you turn on a fan to create white noise, you are essentially creating a source of 1,000
voices. The voice next-door makes it 1,001 voices, and your brain can't pick it out any more.
DIFFERENCE BETWEEN WHITE AND PINK OISE
• Similar to the way white light contains all the wavelengths of the visible spectrum at equal
intensity, white noise has equal power across all frequencies audible to the human ear. Pink
noise is white noise, but with reduced higher frequencies. ... Brown noise lowers the higher
frequencies even more.
• What pink noise is used for?
• In terms of applications, pink noise is often used to test and equalize loudspeakers in rooms
and auditoriums. In recent years, pink noise has also become popular in business settings —
the noise can mask low-frequency background sound, potentially helping to increase
productivity and concentration among employees
• Which is better for sleep pink or white noise?
• There's considerable evidence that white noise is effective for promoting sleep. ... Pink
noise is like white noise, but instead of having equal power across frequencies, pink noise
comes out louder and more powerful at the lower frequencies (think of it as white noise
with the bass turned up)
 SOUND MASKING SYSTEMS
• Sound masking is the addition of natural or artificial sound into an environment to cover-up
unwanted sound by using auditory masking. This is in contrast to the technique of active
noise control
• Sound masking works by subtlety raising the ambient background sound level, thereby
reducing sound's dynamic range. This effectively "masks" unwanted noise, makes speech
unintelligible (creating privacy), and makes the work environment acoustically comfortable.
• Masking is the process by which the threshold of hearing for one sound is raised by the
presence of another sound. ... When the masking and masked sounds come at the same
time, masking is simultaneous. Upward spread of masking is low-frequency sounds masking
high-frequency sounds.
• And even if you are awakened, the soothing quality of white noise can make it easier for you
to fall back asleep. ... The researchers concluded that the white noise was able to mask
environmental sounds, help patients fall asleep, and stay asleep even in a noisy hospital
environment.
 MASKING OF SOUND

• Sound masking does not cancel sound, but it makes conversations

heard at a distance more difficult to understand, and thus less
likely to distract as such conversations at a distance fade into the
background and speech privacy is protected.
BACKGROUND NOISE MASKING SYSTEMS.
• Noise Masking is the addition of natural or artificial sound (such as white noise or pink noise)
into an environment to cover up unwanted sound by using auditory masking.
• Sound masking reduces or eliminates awareness of pre-existing sounds in a given area and
can create a work environment more comfortable, while enhancing speech privacy so workers
can better concentrate and be more productive.
• A typical system is comprised of loudspeakers, amplifiers and a digital sound processor which
is programmed to shape the noise to suit the particular environment.
• The use of well-installed sound masking provides an even dispersion of masking ‘noise’, that
disrupts the intelligibility of surrounding conversations and so creates a less distractive
working environment with greatly enhanced privacy. Concentration and confidentiality are
improved by creating a less distracting environment where employees work far more
effectively and privately.  
 SPEECH PRIVACY
• Speech Privacy can be defined as the inability of an outside listener to understand a
conversation between two or more separate individuals. Effective speech privacy is an
essential aspect of any office as it allows employees to: Conduct confidential conversations
without being overheard.
• Speech privacy operates on a scale of 0% – 100%, where 0% means perfect privacy (no
communication) and 100% means perfect communication (no privacy). Most offices aim to
achieve a speech privacy level of 5%. At this level, most speech will be unintelligible to an
outside listener.
• It is an inability to understand conversations, although some words may still be audible. Two
parameters need to be considered: speech noise levels, and ambient or background noise
levels. The balance between the two will determine the degree of speech intelligibility.
Whenever speech levels exceed ambient noise levels there will be some degree of
communication. Where good communication is needed, for example in a telephone system
or in a lecture hall, the speech to noise ratio is increased by amplifying the speech and
reducing the background noise.
WHY SPEECH PRIVACY IS IMPORTANT
• An open plan office can suffer from two speech problems. First, other people’s conversations
can be a disturbing and irritating distraction; and secondly, confidential conversations can be
almost impossible to conduct. Similar problems also exist in cellular offices, particularly
where acoustic partitions, false ceilings and access floors are installed. Sound flanking paths
are abundant in such situations, even when people remember to close doors. Apart from
noise breakthrough via partitions, flanking over, under and around them, other problem
areas include light fixtures, air conditioning systems.
 ACHIEVING SPEECH PRIVACY
• In order to achieve the desired level of speech privacy, there must be a careful balance
between the noise created by the speaker and the ambient noise in the room.
• When the speaker’s voice is louder than the ambient noise in the room, the speech becomes
non-private, rendering it intelligible to all those within earshot.
• When the speaker’s voice is much lower than the ambient noise, the intended listener will
be unable to understand the speaker.
• When the speaker’s voice and the ambient noise are equal, speech privacy will be at its most
ideal level.
• Communication occurs whenever the speech level exceeds the background noise level, and
conversely, privacy of speech is achieved when the speech level and background levels are
equal. Speech intelligibility ranges from 0% (speech privacy) to 100% (perfect
communication).
• For privacy of speech in office situations the speech intelligibility target is usually about 5%.
This allows some words to be heard, but complete sentences cannot be understood; thus
people’s conversations become less distracting.
• The 5% level can be achieved in three ways:
• Reducing speech level so it is close to background noise levels.
• Increasing the ambient noise level so it exceeds the speech level.
• A combination of the two, i.e. increasing the ambient level slightly and reducing the resultant
effect of speech to achieve speech and ambient level parity.
WHAT SYSTEM IS REQUIRED TO ACHIEVE SPEECH PRIVACY ?

• When increasing the background noise level, a system is needed which is capable of producing
predictable and adjustable results, i.e. a background sound level with precisely controlled
frequency spectrum and amplitude. Sound Masking systems were designed and developed
specifically for this function.
• The basic principle of sound masking is very simple, with sound being generated electronically
and introduced into the open plan area through a number of loudspeakers. The low level
background sound which is thus produced is a combination of frequencies carefully selected to
mask speech and other noises, typically from office machines to achieve speech privacy.