Architectural acoustics

Architecture Acoustics - compilation of all the important parameters involved in acoustical design of any building.

1. ARCHITECTURAL ACOUSTICS
Introduction

2. 16AR 304 | ARCHITECTURAL ACOUSTICS
1. INTRODUCTION
Acoustics, generation,
propagation,
transmission, reception
of sound, sound waves,
frequency, intensity
wavelength, sound
pressure, decibel scale,
reverberation, Sabine’s
formula, echoes,
focusing of sound, dead
spots, flutter echo, Room
resonances, small
enclosures, standing
waves, proportioning of
room dimensions.
2. SOUND TRANSMISSION, ABSORPTION, INSULATION
Reflection, diffusion,
reverberation,
absorption, absorption
co-efficient, Sound
insulation, materials, STC
ratings, sound isolation,
materials, absorption
coefficients.
3.
NOISE CONTROL AND
SOUND REINFORCEMENT
Sources and types of
noise, impact,
transmission, airborne
and structure borne,
transmission loss,
enclosures, path,
Barriers and insulations,
construction details of
cavity walls, composite
walls, floating floor,
wood-joist floors,
plenum barriers.

3. 16AR 304 | ARCHITECTURAL ACOUSTICS
4.
ACOUSTICS IN BUILDING DESIGN
AND CONSTRUCTION
Site selection, shape,
volume, treatment for
interior surface, basic
principles in designing
open air theatres,
cinemas, broadcasting
studios, concert halls,
class rooms, lecture halls,
theatres –Auditorium.
Constructional detailing,
relation to walls/
partition, floor / ceiling/
opening/ windows/
doors. Acoustical
requirement of different
types of buildings.
5.
DESIGN AND DETAILING FOR
ACOUSTICS OF MULTIPURPOSE HALLS
Case studies, Onsite
measurement, Sound
measurement, Design of
a multipurpose hall for
optimum acoustics,
construction details of
acoustical treatment on
walls, ceilings and floors.

4. ACOUSTICS
Architectural acoustics can be defined as the study of the generation, propagation and transmission of sound in
rooms, dwellings and other buildings.
Application of the principles of architectural acoustics can considerably improve the quality of lifeat work, during
leisure time and in the home.
Some sounds are desirableand need to be enhanced or emphasized (e.g. music in a concert hall; the speakers
voice in a debating chamber etc), other sounds are highly undesirable(known as noise) and need to be reduced or
prevented (e.g. noise in a factory workshop; noise from a road traffic etc).

5. ACOUSTICS : VITRUVIUS
•Theater -located away from winds
and from “marshy districts and other
unwholesome quarters”
•Plan and section, sight lines, numbers
and locations of entrances and exits,
and finally considered the subject of
acoustics.

6. ACOUSTICS : WALLACE CLEMENT SABINE
•Wallace clement sabine–“father of architectural acoustics”
•Approached in 1895 to advise to improve the poor acoustics of a
theatre in the university’s foggart museum.
•Need of intelligibility by focusing mainly on maintaining the volume
of the direct sound that reached the listener’s ear.
•Discover the relationship between the dimensions of the roomand
the rate at which a sound became quieter and eventually became
inaudible (rate of decay).
•Plotted a contour map showing the distribution of the sound intensity
-identified the source of the worst sound reflections from the walls
and ceiling and hence reduce themby using sound-absorbing panels
that would break up strong reflections from large plane surfaces.
•Sabine also turned his attention to the design of new theatres and
how best to create a near-uniform acoustic experiencefor every
member of the audience.

7. SOUND
Sound is the sensation perceived by the human ear resulting from rapid
fluctuations in air pressure. These fluctuations are usually created by
some vibrating object which sets up longitudinal wave motion in the air.
There are three characteristics of audible sound:
Pitch: The pitch of a sound is the frequency of its vibration .
Loudness: It is the strength of the sensation received through ear.
Tone quality: It is the characteristic of the sound which distinguishes it
from another sound of same loudness & pitch.

11. SOUND
Two different units for expressing the energy of sound is employed.
1.The intensity of sound is expressed in decibel.
2.Phonis the unit used for measuring the loudness sensation in the ear.

14. REFLECTION
ABSORPTION
REFRACTION

15. DIFFUSION
DIFFRACTION TRANSMISSION

17. Reverberation time in seconds Acoustics
0.50-1.50 Excellent
1.50-2.00 Good
2.00-3.00 Fairly Good
3.00-5.00 Bad
Above 5.00 Very Bad

38. GENERAL PRINCIPLES OF DESIGN : SITE SELECTION
•The problem of noise is an important consideration. A noise survey
of the site should be made in advance.
•In fact, the quietest possible condition should be provided so that
intelligibility of speech does not suffer.
•When air-conditioning is provided special careshould be taken to
attenuate the plant noise and the grill noise. For this purpose plant
should be suitably isolated and ducts as well as the plenum should
be so designed that noise gets adequately reduced so as to be
within the permissible limits.
•Depending on the ambient noise level of the site, orientation, layout
and structural designshould be arranged to provide necessary noise
reduction, so that the background noise level of not more than 40 to
45 dB (as measured on 'A' scale of sound level meter) is achieved
within the hall.

39. GENERAL PRINCIPLES OF DESIGN : SIZE & SHAPE
•The size should be fixed in relation to the number of audience required to
be seated.
•The floor area of the hall including ,gangways ( excluding the stage) should
be calculated on the basis of 0.6 to 0.9 sq.mper person.
•The height of the hall is determined by such considerations as ventilation,
presence ( or absence) of balcony and the type of performance.

40. GENERAL PRINCIPLES OF DESIGN : SIZE & SHAPE
•The average height may vary from 6 m for small
halls to 7·5m for large halls.
•Ceiling may be flat but it is preferable to provide
a slight increase in the height near the centreof
hall.
•The volume per person required to be provided
should normally range between 3·5 to 5.5 cub.m.
•Suitable volumes for different types of auditoriums
are given below but it is recommended that higher
values be adopted only in special cases:
Auditorium Aquila by Renzo Piano Building Workshop

41. GENERAL PRINCIPLES OF DESIGN : SHAPE
•In terms of plan geometry, existing halls currently used can be
classified into three groups: those based on a rectangular plan,
horseshoe-shaped plan and fan-shaped plan.
•The resulting geometric features are directly related to their
acoustic properties.
•The main acoustic parameter of enclosed spaces is the
reverberation time.
•For halls based on rectangular and fan-shaped plans, the
reverberation time found theoretically is consistent with the
acoustic measurements, whereas for halls based on horseshoe
plan the measurement results are lower than those determined
theoretically. This is especially the case of opera houses with
auditorium capacities below 1000 seats, which are the most
numerous.

43. SHAPE: RECTANGULAR HALL
Halls with a rectangular plan have side walls that ensure short
first reflection times,but the large parallel surfaces often
result in acoustic defects, such as flutter echoes and standing
waves.

44. SHAPE: RECTANGULAR HALL

45. SHAPE: FAN-SHAPED PLAN
•Halls with a fan-shaped plan make it
possible to accommodate a large
audience while providing good
visibility and acoustics. The shape of
the hall prevents the formation of
flutter echo by side walls, though the
sound reflected from the rear wall can
reach the front of the auditorium with
a significant delay. This can be
prevented by covering the rear wall
with a sound diffusing or absorbing
structure.

46. SHAPE: FAN-SHAPED PLAN

47. SHAPE: FAN-SHAPED PLAN

48. SHAPE: HORSE SHOE PLAN
•Halls with a horseshoe plan ensure good visibility,
a sense of proximity to the sound source and
mutual eye contact between the spectators.
•A large number of boxes and rich interior décor
contribute to sound dispersion, which conceals
possible acoustic defects and ensures the proper
ratio of direct to reverberated sound.
•The large number of listeners and the presence of
boxescan result in excessive attenuation of the
hall,thus preventing the recommended
reverberation time from being attained.

49. SHAPE: FAN-SHAPED PLAN

50. 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 music performance.

51. SHAPE
•Floor plans of various shapes are used, but the one which is considered to give satisfactory results without introducing
complications in the acoustical treatment of the hall is the fan-shaped plan.
•The side walls should be arranged to have an angle of not more than 100 degrees with the curtain line.
•In the case of talking pictures synchronization of sound with lip movement is most essential.
•Also, in the case of theatres a person with normal vision should be able to discern facial expressions of the
performers.In order to satisfy these conditions, it is recommended that the distance of the farthest seat from the
curtain line should not normally exceed 23 meters.

52. STAGE :
It would be large for theatres, while it would be comparatively small for cinema
halls which again depends on the size of the screen.
REAR WALL:
•The auditorium rear wall(s) should be either flat
or convex in shape.
•This should not be concave in shape, but where
it cannot be avoided, the acoustical design shall
indicate either the surface to be.
•Splayed or convex corrugations given in order to
avoid any tendency for the sound to focus into the
hall.
SIDE WALLS :
•Where the side walls are non-parallelas in the case of a fan-shaped hall the walls
may remain reflectiveand may be architecturally finished.
•Where the side walls are parallel they may be left untreated to a length of about
7.5m from the proscenium end.
•In addition, any of the surfaces. likely to cause a delayed echo or flutter echo should
be appropriately treated with a sound absorbing material.
•Difference between the direct path and the path reflected from side wall shall not
exceed 1m.

54. ROOF AND CEILING:
•In large halls a false ceiling i.eusually provided
below the trusses.
•The portion of the false ceiling near the proscenium
is constructed of reflective material( usually plaster
of Paris) and is suitably inclined to help reflections
from the stage to reach the rear seats of the hall.
•The remaining portion of this ceiling is constructed
to take acoustical treatment. Concave shaped
ceilings (in the form of dome or barrel) should be
avoided.
•The rear portion of the ceiling may be treated with
sound absorbing material partly for control of
reverberation and partly to prevent build-up of
audience noise.

55. FLOOR :
•For good visibility as also for good listening conditions, the successive rows of
seats have to be raised over the preceding ones with the result that the floor
level rises towards the rear.
•The elevation is based on the principle that each listener shall be elevated with
respect to the person immediately in front of him so that the listener's head is
about 12 cm above the path of sound which would pass over the head of the
person in front of him.
BALCONY:
•Where a balcony is provided, its projection into the hall should not be more than
twice the free height of the opening of the balcony recess.
LINE OF SIGHT
The elevation of the balcony seat should be such that line of sight is not inclined
more than 30 degrees to the horizontal.

59. FOYER AND ATTACHED ROOMS:
•The foyer area, number and size of entrances also depend on the size and
seating capacity of the auditorium.
•At least 20 percent of the seating area of the hall is recommended for foyer.
•For lobby and lounge, areas at least corresponding to 10 percent of the seating
area in the' hall are recommended.

60. SEATS
•The seats should be arranged in concentric
circle drawn with the centre located as its
distance from the auditorium rear wall.
•The angle subtended with the horizontal at
the front-most observer by the highest object
should not exceed 30 degrees.
•On this basis, the distance of the front row
works to about 3-6 m for drama and it should
be 4.5 m or more for cinema purpose.
•Minimum distance of front seats should be
determined by the highest point required to be
seen on the stage which is usually raised by
about 75cm or more.
•The width of a seat should be between 45 cm
and 56 cm.

63. •The back to back distance of chairs in successive rows of seats shall be at least
85 cm. If extra comfort is required higher spacing may be provided which shall
vary between 85cm and 106 cm.
•Seats should be staggered sideways in relation to those in front so
that a listener in any row is not looking directly over the head of-the person in front
of him.
•Upholstered seats shall be provided, wherever possible, so that the acoustic
characteristics of the hall are, not appreciably affected by fluctuating audience
occupancy. This is particularly important for halls where the audience provides the
major part of the required sound absorption.

64. ADDITIONAL REQUIREMENTS FOR OPEN -AIR AUDITORIUMS AND CONFERENCE HALLS
OPEN AIR AUDITORIUM:
•Prevailing noise conditions should not exceed 45 dBon 'A' scale. Wind velocities
naturally experienced at site should not exceed 16 km/h.
•Back stage wall should be made reflective and broken into convex shaped
surface.
•Overall shape should be flat in plan; however, if it is desired to be concave, it
should be broken into convex surfaces which in either case should be of at least
90 to 180 cm width.

68. •Depth of stage should be arranged to suit individual requirements; where it
exceeds 6 m, it is necessary to treat back stage wall acoustically.
•A ceiling reflector should be provided for directing the sound to the rear seats.
•This reflector may be a hard reflecting surface slanting at a suitable angle
towards the audienceand fixed over the main sound originating area of the
stage.
•If direction of wind generally remains the same, the auditorium should be so
located that wind direction is towards the audience from the stage.
•Even if reflectors are provided as recommended sound amplification should be
resorted to in case the number of audience exceeds 600 or back ground noise is
more than 45 to 50 dB. The loudspeaker system should be so designed that it is
capable of providing an average level up to 80 dB over the entire listening area.

69. ACOUSTICAL REQUIREMENTS
HALLS USED FOR SPEECH AND DRAMA:
The clarity of speech is most important in this case.
Optimum clarity depends on:
a)correct reverberation time,
b)absence of echo,
c)correct loudness level at all parts of the hall, and'
d)low background noise,
HALLS FOR MUSIC:
•Adequate reverberation is important to lend proper blending and fullness of
music.
•The reverberation time is required to be higher than for halls meant for speech
only.

108. DESIGN: 26.03.2020
•Design a multipurpose hall or auditorium of 500 seating capacity and do the
required acoustics details and material selection.
•DELIVERABLES:
1.Plan –To suitable scale,
2.Section –To suitable scale,
3.Acoustic Panel Details –To suitable scale,
4.Material Board.

109. PLAN –SECTION –MATERIAL BOARD

110. ACOUSTIC PANEL DETAILS