2. Acoustics is the science of sound which assures the
optimum conditions for producing and listening to
speech, music etc.
Acoustical design and construction is done to for
dissipation of the noises, external and internal and
insulation against sound.
Acoustics can be achieved by considering two aspects:
proper control and remedy of the acoustical
defects in buildings
sound insulation
3. Acoustics and Sound
Insulation
Medium: Solid, liquid & Gas.
velocity of sound depends on nature and
temperature of medium.
Frequency or pitch: Number of cycle or vibrations /
sec. Greater is no. of cycle higher will be the pitch.
Pitch is the measure of quality of sound.
4. What is Sound?
Intensity or loudness of sound: flow of sound
energy /sec through unit area.
intensity is a measure of quantity of sound energy
Measurement of Sound: unit - Bel = 10 dB
Ear doen't respond in proportion to the intensity of sound,
and that its response in proportional to the logarithm of
the intensity of sound.
5. Sounds or Noises Intensity level (dB) Feeling of
sound
Range Average
Pneumatic drill or aeroplane at
a distance of 4 m.
120-140 130 Pain &
Discomfort
Thunder, Air plane motors 100-120 110 Deafing
Noisy factory areas, loud
street noise
80-100 90 very loud
Noisy home, average
conversation
40-60 50 moderate
Quiet living room, quiet
conversation and avg
auditorium
20-40 30 faint
6. Acceptable Indoor Noise Level
Location Noise Sources in Different
Buildings
Noise Levels
(dB) range
Radio and TV studios 25-30
Music Room 30-35
Hospital Auditoria 35-50
Apartments, hotels, & homes 35-40
Conference rooms , small offices, and
libraries
35-40
Court rooms and class rooms 40-45
Large public offices, banks and stores 45-50
7. Behaviour of Sound
Sound originated from any source either as a speech or music, it is
transmitted from the source in all directions.
Sound travels till it strikes on some surface from where, a part of it
is reflected back, a part being absorbed, or transmitted.
Reflection Coefficient: ratio of the reflected intensity
over the incident intensity
Absorption Coefficient: ratio of energy absorbed by the area to the
energy striking.
Transmission loss: reduction in intensity of sound in passing through
the barrier or measure of the effectiveness of a barrier or surface in
insulating against the transmission of sound.
8. Acoustical Defects
Echoes: Echo is an indirect or a reflected voice which is heard just
after the direct hearing of the voice coming from the same sound
source. Echo forms when time lag between the two voices or sound is
about 1/17th of a sound and the reflecting surfaces are situated at a
distance greater than 15m.
o Reverberation: Prolongation of sound after the source producing
it has died out.
Reverberation time:
t >5 sec
5>t >3 sec
3>t >2 sec
2>t >1.5 sec
- very bad
- bad
- fairly good
- good
1.5>t >0.5 sec - very good
Reverberation should be short for auditorium as a cinema theatre or public
address.
9. Sound Foci: when reflected sound rays meets at a point which causes
concentration effect for the reflected echoes and creates a sound of
large intensity.
Dead Spot: Side effect of sound foci. deficiency of reflected sound
rays causes low sound intensity at some points.
Insufficient loudness: In large auditorium, due to lack of sound
reflecting flat surfaces near the source or stage and excessive
absorption of sound in the hall, results in this defect of insufficient
loudness.
Exterior Noise or Outdoor Nuisance: cause mainly due to poor sound
insulation an partly due to poor planning.
Acoustical Defects
10. Defects and Recommended Remedies
Defect Causes
Recommendation
New Design Existing Design
Excessive
reverberation
Insufficient
Absorption
Add absorbents Add absorbents
Echoes unsuitable shapes &
proper reflecting
surface
avoid unsuitable
shapes & make
offending surface
highly absorbent
-
Sound Foci Concave reflecting
interior surfaces
avoid curvilinear
interior
use absorbents on
focusing surface
Deat spots Irregular
distribution of
sound
provide even
diffusion of sound
introduce suitable
diffusers
Insufficient sound
volume
lack of reflections
close to source of
sound or excessive
absorption
disposition of hard reflecting surfaces
near the source of sound.
adjust absorption to give optimum
reverberation
11. Acoustics -Requirements and conditions
Adequate sound intensity.
Evenly distributed
Clear and distinct
Reach the audience with the same
frequency and intensity
Noise protection to be done
12. Factors in Acoustical
Design
Site Selection
Volume
Shape
Interior Surface
Reverberation
Seating arrangements and audience
Sound Absorption
13. Factors in Acoustical
Design
Site selection:
if possible, site should be away from busy
street, railways, airports, etc
if not, then orientation, layout, structural
design should be done accordingly.
Noise reduction
14. Factors in Acoustical
Design
Volume:
Puropose of hall.
Height is of greater
importance.
Public lecture hall - 2.8 to 3.7 m3/person
Musical Concert Hall - 4.2 to 5.6 m3/person
Cinema Theatres - 3.7 to 4.2 m3/person
15. Factors in Acoustical
Design
Shape:
For correcting the defects.
For better distribution of sound.
Ceiling height for a room or hall to be
used for speech and music is kept
varying from 1/3rd to 2/3rd of the
width of the room.
16. Relationships between ratio & Vol per
seat
Type of
Auditorium
Vol./per
seat in m3
Ratio of
H:W:L
Approx
Capacity in no.
of person
Lecture Hall
(Small)
2 - 3 1:1.5:3 150 to 300
Lecture Hall
(Large)
3.5 1:2:4 400 to 500
Lecture halls
with loud
speakers
4.5 1:2.5:5 500 to 1000
Cinema 3.5 to 4.5 1:2:3 800 to 1000
(normally)
Theatre
(Drama)
3.5 to 4.5 1:2:3 upto 750 (small
theatre)
17. Factors in Acoustical
Design
Treatment of interior surfaces:
Provide favourable reflections
Tilted portions of the ceiling can be
arranged
Max time gap between sound
source and listener should be 45
milli-sec
ceiling and wall reflector should be
within 8m of the sound source.
18. Cont.
..
Path difference between direct and
reflected sound at no listening point
should exceed 12 m.
Plain side wall are normally found
suitable.
Concave ceiling surfaces such and
domes should be avoided.
smooth ceiling should not be
parallel to floor
19. Cont.
..
Convex shaped wall considered best
Rear wall should not be provided as
concave walls unless treated with
sound absorbent
21. Factors in Acoustical
Design
Seating Arrangements:
largest contributer to the absorption
of sound
distance of front row should be
about 3.5 m for drama and 4.5m for
cinema.
Width of seat 45 to 55cm.
Back to back distance - 85 - 105 cm
22. Factors in Acoustical
Design
Sound absorption:
Usefull positioning of the sound
absorbing material.
coefficient absorption for distemper
is higher than paint.
wood panel has higher coefficeint at
lower frequency.
23. Acoustical
Treatment
Open Air Theatres:
Selection of site is most important.
Avg noise level should not exceed
40 dB.
Slope of seating area should not be
less than 12 degree.
Sound amplification system
24. Acoustical
Treatment
CinemaTheatres for Sound Films:
Fan shaped floor plan with diverging
side wall.
Splayed type ceiling with slight
upward slope towards the rear end.
Ratio (H:W:L) should be approx
1:2:3.
Surface near sound source should
be hard polished.
Vol - 3.5-4.5 m3.
25. Acoustical
Treatment
Radio Broad Casting Studios:
Perfect Sound Proofing/Noise
insulation:
Floor, walls, & ceiling must be rigid
material.
Variable reverberation time:
Different absorption is required in the
same room as suitable for type of
studio.
Noise level - 25-30 dB.
26. Acoustical
Treatment
Radio Broad Casting Studios:
Ratio of H:W:L - 2:3:5.
Shape should be rectangular with flat
ceiling.
Provision of window should be min.
Air tight.
Heavy Curtains can be used
27. Acoustical
Treatment
Class Lecture Rooms:
Room dimen - 7:8.5:4 considered
satisfactory for 40 students.
Length to width - 1.2 to 1(wide rooms
are more satisfactory.
Noise level- 40dB.
t - 0.75 sec at freq.(500-2000) & 9 sec
at freq.(125CPS)
Vol per can be kept as small as
possible
- 12m2 or less.
28. Classification of Sound
Absorbents
Porous Absorbents:
Sound waves strike surface of a porous
of a material, a part of sound waves gets
reflected while the other part enter the
porous material.
The part of reflected waves energy is
reduced while , the part of waves that
entered into the porous material is
converted into heat
rock wool, glass wool, foamed plastics,
asbestos fibre, curtains, spray felt etc.
30. Classification of Sound
Absorbents
Cavity Resonators:
When sound waves enter the resonator;
due to multiple reflections inside , the
sound waves are absorbed .
The cavity resonator may be designed
to absorb sound of any particular
frequency generated by machines such
as air conditioner plant,
machines etc.
31. Classification of Sound
Absorbents
Composite Type-Absorbents:
A composite absorber is a single unit
which does the function of the other three
absorbers mentioned before.
The composite absorber of a perforated
panel fixed over an air space
containing porous absorbent.
When sound waves strike the panel, they
pass through it and damped by resonance
of the air in the cavity.
33. Nois
e
Classification based on their origin:
Oudoor Noise: source of origin outside
from the room or building.
Road traffic, railways, aeroplanes,
loudspeaker, moving machineries
Indoor Noise: source of origin inside the
room.
conversation of occupants,
banging of doors, footsteps, etc.
34. Nois
e
Classification based on analysis of sound
insulation problem:
Airborne Noise: generated in the air & is
transmmitted through air.
Structure Borne or Impact Noise:
originates and progress in the building
structure.
caused due to structural vibration
35. Sound
Terminology
Sound Absorption: prevention of reflection of
sound waves
Sound Insulation: prevention of transmission
of sound
Sound Structure: indicate loss of sound energy
on reflection at a surface.
Transmission loss: reduction in sound
intensity during the transmission of air-borne
sound from the source to the recipient.
36. Max Acceptable Nosie
SNo. Type of building /structure Noise level (dB)
1 Studios for radio broadcasting 25-30
2 Auditoriums 35-40
3 Small offices, court room, libraries
40-45
4 Hospitals 40-50
5 Lecture Rooms 45-50
6 Residential Building 45-55
7 Large Offices 50-60
8 Factories 60-65
37. Noise Control & Sound Insulation
General Consideration:
Isolate it at source
Selection of location and orientation
Lining of wall and ceiling by means of airfilled
materials, like felts, straw boards etc
Rigid wall, floor, partitions can prevent
transmission of noise
struture borne noise can be prevented by
introducing discontinuities in the path of vibrating
waves or expansion joint.
personal protective devices - ear plugs, head
phones etc.
38. Noise Control & Sound Insulation
Constsructional Measures:
Wall and Partitions
Floor and Ceilings
Windows and Doors
Insulating Sanitory Fittings
Machine mounting or Insulations of Machinery
39. Noise Control & Sound Insulation
• Wall and Partitions(vertical barriers):
Rigid and Homogenous Patitions: Thickness of wall
affects the sound insulation property.
Partitions of Porous Material:Porous Concrete
Masonry, cinder concrete etc. 10%
more absorbent than non porous.
Hollow & Composite Partition walls or Double wall
Construction:Composite partition of cavity wall
type construction by filling the cavity or leaving
the air space with some resilient material
40. Noise Control & Sound Insulation
Floor &
Ceilings(Horizontal
barrier to noise):
Use of resilient material
on floors.
41. Noise Control & Sound Insulation
Floor & Ceilings(Horizontal barrier to
noise):
Providing a floating floor construction:
Additional floor float over the existing
surface by means of resilient
material.
48. SOUND
LEAKS
• Doors: Hollow core doors are poor sound blockers. When privacy is a
key consideration, doors should be solid wood or have insulated cores,
and should be gasketed to prevent sound from passing between the
door and the jamb or sill.
• Windows: Double pane and/or storm windows reduce sound
transmission. Weather stripping helps. Windows facing exterior noise
sources should be small and as few as possible. Double-hung
windows should be able to be tightly closed.
• Wiring and piping: Holes through which wiring or conduit passes
should be sealed or caulked. Cutouts for electrical outlet boxes should
be made precisely so boxes will fit snugly. Do not install electrical
outlet boxes opposite each other on each side of a wall; these should
be staggered. In bathrooms on opposite sides of a wall, medicine
cabinets should be staggered. Holes cut out for piping should be
sealed with caulking. Just stuffing the holes with insulation is not
sufficient. Sound can easily pass through porous insulation. One can
stuff the holes with insulation and then caulk over the insulation.
50. NOISE REDUCTION BETWEEN ROOMS
• Every building, must be designed and constructed in such a way
to limit the transmission of source noise from normal domestic
type activities, through a wall or floor, between a room and
internal space where noise is likely to occur, to a level that will
not cause inconvenience to the building occupants.
Limitation:
• This standard only applies to a wall or floor forming an apartment
in a dwelling and a room in a residential building which is
capable of being used for sleeping; other than:
• a wall between an en-suite bathroom and the apartment or room
it serves
• a hospital
• a place of lawful detention.
54. NOISE REDUCTION WITH LANDSCPE
ELEMENTS
• This method uses plants to entrap or absorb sound vibrations. It is the
most commonly used, particularly for large scale applications.
• Sound is absorbed by all parts of the plant such as leaves, branches, twigs and
wood. The rougher the bark the better it absorbs sound. Experts say the best
species for this will have many branches and thick, fleshy leaves with thin
petioles (leaf stem).
• These broadleaf species lose their effectiveness in the winter when
deciduous. Fortunately they leaf out for maximum advantage during the
months when windows are open and you're spending time outdoors. In warm
climates many more broadleaf evergreens can be used for sound absorption
benefits all year around.
• Asound attenuation barrier is most effective when located closest to the
source of the sound.
• Large shrubby trees can also be effective at scattering sound waves. The deeper
and more dense the barrier the greater its scattering potential. This illustrates
the biggest problem: your designer needs space for an effective solution.
57. NOISE REDUCTION AND BUILT FORMS
Noise from outside a building is
reflected
around a balcony space.
Ascreen wall is built between a noise
source
and a house
58. LAND USE PLANNING FOR NOISE CONTROL
• Noise planning controls may operate at either of
two scales. At a larger planning scale are general
land use allocation noise controls.
• These are primarily allocations of various types of
development within a larger landscape context (such as
a town) to appropriate noise-environment zones.
• In other words, noise-sensitive land uses are allocated to
quieter zones and noisier land uses are allocated to
noisier zones.
• Noise control is for the most part a matter of isolating or
aggregating land uses to prevent the undesirable exposure
of noise-sensitive areas. At this scale, specific types of
noise buffers between uses are not considered.
59. THREE STEPS TO NOISE CONTROL SOLUTIONS
• 1. Locate the source of noise The first step in noise control is to investigate the real
noise source. It has been mentioned that noise control problems may involve merely moving
the source farther from the receiver, adjusting or repairing the source if it is a piece of noisy
equipment, or replacing it. If none of these work, an acoustically efficient enclosure will have
to be designed. Once the true source has been identified, the next step is to measure the
noise.
• 2. Measure the noise Asound level meter is used to measure the noise level at several
locations — at its source, along its path, and at the receiver or listener’s location — using
the A- weighted scale and also measuring the sound level in octave or third-octave bands.
Sound level meter readings will not only provide sound pressure (loudness) levels at various
locations, but will also show which frequencies are most offensive to the listener. This data
will be helpful in selecting acoustical materials with sound absorption and/or sound
reduction properties best suited to the particular application.
• 3.Noise from central equipment: When operating heating and air-conditioning
equipment, a good guideline is “lower and slower”: lower volumes of air moved through the
system with fans and blowers operating at a slower speed. Central air equipment should also
be acoustically isolated from spaces where airborne noise would be objectionable. Equipment
should be mounted on vibration isolators to avoid transmission of structure borne noise.
Sound traps or baffles will help to attenuate equipment noise in adjacent ductwork.
