Building services

3/21/2022
UNIT IV
FUNDAMENTALS OF ARCHITECTURAL
ACOUSTICS
ARC323-BUILDING SERVICES III
By
VIJESH KUMAR V
ASSISTANT PROFESSOR,
SPA VIJAYAWADA
vijesh@spav.ac.in , +919487005023
1
SYLLABUS
2
Unit IV Fundamentals of architectural acoustics 6
Fundamentals: Sound waves, frequency, amplitude, decibels, logarithms,
measurement versus perception, addition and subtraction of decibels. NC
curves. Material property: Absorption, reflection, scattering, diffusion,
transmission, absorption co-efficient, NRC, sound transmission class (STC),
impact insulation class (IIC).
31.01.2022
Fundamentals: Sound waves, frequency, amplitude, decibels,
logarithms, measurement versus perception, addition and
subtraction of decibels. NC curves.
3
IMPORTANCE OF STUDYING ACOUSTICS
1. The handling of wanted sound
2. The handling of unwanted sound
4

3/21/2022
17
Decibels [dB]:
The decibel is used in acoustics as the standard unit of sound pressure
level, or the loudness of a sound. Keep in mind that sound pressure
increases on a logarithmic scale. As a general rule of thumb, an increase
of 10 dB means the sound is perceived to be twice as loud – however this
can vary based on the type of sound and the listening conditions.
Humans can just barely detect a 3 dB sound level difference. They can
easily detect a 5 dB change in sound level under most conditions.
18
19 20

3/21/2022
45 46
47
MOLECULAR ATTENUATION
48

3/21/2022
49
ACROSS
50
ACOUSTIC SHADOW
51
DIFFRACTION
52

3/21/2022
Addition and Subtraction of Decibels
Sound levels are generally expressed in decibels, which are logarithmic and so cannot be manipulated without being converted
back to a linear scale. You must first antilog each number, add or subtract and then log them again in the following way:
Fundamental of Acoustics Part 5 Decibel Additions, Subtraction and Averaging
https://www.youtube.com/watch?v=Qnz4uKnJWww
Decibel addition equation: Decibel subtraction equation:
62
63 64

3/21/2022
69 70
SOUND PRESSURE LEVELS ARE
MEASURED FOR DIFFERENT
FREQUENCIES AS:
•62.5 Hz : 40 dB
•125 Hz : 50 dB
•250 Hz : 55 dB
•500 Hz : 60 dB
•1000 Hz : 50 dB
•2000 Hz : 55 dB
•4000 Hz : 45 dB
•8000 Hz : 45 dB
71 72

3/21/2022
73
07.02.2022
Material property: Absorption, reflection, scattering, diffusion,
transmission, absorption co-efficient, NRC, sound transmission
class (STC), impact insulation class (IIC).
74
ACOUSTIC MATERIAL PROPERTY
SOUND ABSORPTION
Sound absorption is defined as the loss
of sound energy when sound waves
come into contact with an absorbent
material such as ceilings, walls, floors
and other objects.
SOUND ABSORPTION

3/21/2022
SOUND ABSORPTION
Imagine you are watching a band play in the
auditorium. If the entire space were covered
with sound-absorbing materials, then the
walls would have absorbed too much sound
and make the music sound flat. The musicians
would also have to work hard in order to not
make any mistakes. However, some
reverberation would help the music ring
sounds beautiful, as long as there’s not too
much echo produced. There is also a chance
of sound transmission from one room to
another. Just like sound absorption, certain
materials are used for blocking sound. sound
insulation is used to control sound between
rooms.
SOUND REFLECTION
If a sound is not absorbed or transmitted
when it strikes a surface, it will be
reflected.
the angle of INCIDENCE of a SOUND
WAVE equals the angle of reflection,
However, this law of reflection holds only
when the WAVELENGTH of the sound is
small compared to the dimensions of the
reflecting surface, else diffraction takes
place.
Sound reflection gives rise to
DIFFUSION, REVERBERATION and ECHO.
SOUND REFLECTION
Here are some important terms defined below
to understand the reflection of sound in a
better way as:
1. Echo – Repetition of sound caused by the
reflection of the sound wave.
2. Reflection of Sound Waves – The bouncing
back of the sound wave on striking a
surface such as a wall, metal sheet,
plywood, etc. is called the reflection of the
sound wave.
3. Reverberation – If the distance is less than
17 m, then the original sound mixes with the
reflected sound. Due to repeated
reflections at the reflecting surface, the
sound gets prolonged. This effect is known
as reverberation.
SOUND REFLECTION
80

3/21/2022
SOUND SCATTERING
Scattering is the specular reflection of a
wave from small segments of a rough
surface.
Since usually we do not know details about
the small reflecting planes of a rough
surface, we treat scattering in geometrical
acoustical analyses by using a scattering
coefficient which tells us the fraction of the
incident sound that is not specularly
reflected.
To further complicate matters, scattering is
inherently related to the ratio of wavelength
to the dimensions of the surface irregularities.
Sample Scattering Coefficients at Different Frequencies
SOUND DIFFUSION
Diffusion in simple terms is the scattering
of sound energy.
Installing sound diffusers interrupt
discrete echoes by scattering or diffusing
sound energy over a wide area without
removing it from the room. This
maintains sound clarity and improves
speech intelligibility.
SOUND DIFFUSION
So how do acoustic diffusers work?
Unlike sound absorption panels that are
made of soft materials with lots of air
pockets that prevent sound waves from
bouncing back at you, a sound diffuser
allows for the sound to reflect—but it
breaks up the reflection so you don’t get
a clear echo.
SOUND TRANSMISSION
Acoustic transmission is the transmission
of sounds through and between
materials, including air, wall, and musical
instruments. The degree to which sound is
transferred between two materials
depends on how well their acoustical
impedances match.
Acoustic impedance (Z) is given by the
ratio of the wave’s acoustic pressure (p)
to its volume velocity (U).

3/21/2022
SOUND TRANSMISSION
1. Airbourne
2. Structurebourne
1. Impact
2. Flanking
SOUND ABSORPTION COEFFICIENT
Sound Absorption, sound energy is
'absorbed' by the different media that
sound waves encounter, along their
transmission path, from the source to the
receiver.
An open window is an example of 100%
sound absorption i.e. no reflection,
whereas bathrooms usually have sound
reflective surfaces and therefore very
low sound absorption properties,
resulting in multiple reflections in the
room and a diffused sound field.
SOUND ABSORPTION COEFFICIENT
The sound absorption coefficient or Sabine
absorption coefficient is the ratio of
absorbed sound intensity in an actual
material to the incident sound intensity and
can be expressed as
α = Ia / Ii
where
α = sound absorption coefficient
Ia = sound intensity absorbed (W/m2)
Ii = incident sound intensity (W/m2)
Sound Absorption is the product of sound
absorption coefficient and surface area of a
material, the units are Sabine.
NOISE REDUCTION COEFFICIENT
A Noise Reduction Coefficient is an
average rating of how much sound an
acoustic product can absorb.
NRC is a single number rating system
used to compare the sound absorbing
characteristics of building materials. A
measurement of the acoustic absorption
performance of a material, calculated
by averaging its sound absorption
coefficients at 250, 500, 1000 and
2000 Hz, expressed to the nearest
multiple of 0.05.

3/21/2022
NOISE REDUCTION COEFFICIENT
91 92

3/21/2022
97
SOUND TRANSMISSION CLASS (STC)
STC is an integer rating of how well a
building partition attenuates airborne
sound.
The STC is useful for evaluating
annoyance due to speech sounds
STC is measured roughly by the decibel
reduction in noise a material/partition
can provide, abbreviated 'dB‘.
Most “soundproof” products have an STC
rating in the range of 35 – 55.

3/21/2022
IMPACT INSULATION CLASS (IIC)
IIC is a rating for the ability of a floor-
ceiling assembly to block
impact/structure-borne noise from
transmitting to the space below.
A floor-ceiling assembly with a low IIC
rating will potentially cause distracting
noise in the room below, leading to
possible annoyance and problems with
communication.
In new construction, gymnasia, dance
studios, or other high floor impact
activities shall not be located above core
learning spaces.
IMPACT INSULATION CLASS (IIC)
TYPES OF SOUND ABSORBING MATERIALS TYPES OF SOUND
ABSORBING MATERIALS
Porous absorbents
Typical porous absorbers are carpets, acoustic tiles,
acoustic (open cell) foams, curtains, cushions, cotton
and mineral wool
Cavity resonators
Panel absorbents
Composite absorbents

3/21/2022
TYPES OF SOUND ABSORBING MATERIALS
Cavity resonators
Panel absorbers
UNIT V
ACOUSTICS OF ARCHITECTURAL SPACES
ARC323-BUILDING SERVICES III
By
VIJESH KUMAR V
ASSISTANT PROFESSOR,
SPA VIJAYAWADA
vijesh@spav.ac.in , +919487005023
106
SYLLABUS
107
Unit V Acoustics of Architectural Spaces 9
Reverberation time, sound in enclosed space, basic room acoustics
concepts and design, design of auditorium, conference hall, recording
studio and class rooms. Environmental noise and its control.
Lab: Introduction to sound level meter. Simple experiments to predict RT,
Background noise level and frequency analysis.
14.02.2022
Reverberation time, sound in enclosed space, basic room
acoustics concepts and design,
108

3/21/2022
REVERBERATION TIME
109
111

3/21/2022
BEHAVIOR OF SOUND IN AN
ENCLOSED SPACE
129
BEHAVIOR OF SOUND IN AN ENCLOSED SPACE - 1
1. Reduction in its intensity of sound
2. Absorption of direct sound by the
audience
3. Absorption of direct and reflected
sound by surfaces
4. Reflection of sounds from right-
angled corners
130
Shape, dimensions, construction, and contents of any room will determine how sound is transmitted,
reflected and absorbed. The way in which sound behaves in an enclosed space depends on the
following factors:
BEHAVIOR OF SOUND IN AN ENCLOSED SPACE - 2
1. Dispersion of the sides of an
enclosure
2. Edge diffraction of sound
3. Sound shadow
4. Primary reflection
5. Panel resonance
131 132

3/21/2022
133
The two major factors that affect sound
transmissions are:
• Increased weight per unit area of
panel decreases sound transmission,
• Increased frequency of incident sound
decreases sound transmission.
Besides the mass of the panel, other
factors that can affect sound transmission
include:
• Panel stiffness
• Rigid panels
134
GENERAL REQUIREMENTS FOR SPEECH
INTELLIGIBILITY
The requirements for speech intelligibility are basically the same for un-amplified as
for amplified speech. The most important factors are:
1. Speech level versus ambient noise level
2. Reverberation time
3. Direct-to-reverberant ratio
135
BASIC ROOM ACOUSTICS CONCEPTS
AND DESIGN
136

3/21/2022
137
1. NARROW ROOMS
Placing the sound absorbing materials on
the ceiling in a narrow room will not
create the wanted acoustic effect.
Sound absorbers must be placed as
close to the sound source as possible.
Therefore, the absorbing materials must
primarily be placed on the walls
138
2.ROUND ROOMS
The sound moves towards the constructive
centre thereby creating echoes.
The sound diffusing elements should be
placed on the curved surfaces in order
for the sound to be dispersed in many
directions.
139
3.1 LARGE ROOMS WITH LOW CEILING
In large rooms the sound spreading is
experienced as the greatest challenge,
since the speech sounds can be heard
over long distances.
Sound absorbing and sound diffusing
materials should be used, and sound
barriers should be applied to the ceiling.
The sound regulation from the floor is
secured by furniture and the use of
sound barriers.
140

3/21/2022
3.2. LARGE ROOMS WITH HIGH CEILING
The acoustic environment in large rooms is
sometimes experienced as the one at a railway
station. This is partially connected to the fact
that it is difficult to concentrate due to the
relatively high noise level. Another reason for
this is the fact that the conversation over short
distances is impeded due to the sound being
masked or drowned by the surrounding noise
It is therefore important that all the available
surfaces are equipped with effective sound
absorbers and sound diffusers. The furniture
along with the sound barriers play a highly
active role by diffusing the sound and thereby
making the existing sound absorbers and
diffusers even more efficient.
141
4. SMALL ROOM WITH PARALLEL WALLS
In small rooms, the low frequencies often
seem to be predominant. Therefore, the
speech appears to consist primarily of
humming sounds. Sound absorbers with a
low-frequency profile should be used
and placed on the ceiling surface.
142
5. CEILING DOMES
The sound diffusing elements should be
placed on the curved surfaces in order
for the sound to be dispersed in many
directions.
143
6. INCLINED CEILING
Inclined ceilings have both a sound spreading
and a sound concentrating effect. In most
cases, the sound is concentrated because the
sound regulation of the area around the
inclined ceiling has not been considered
carefully.
The wall area opposite the inclined ceiling
should also be equipped with sound
absorbing materials. As a principal rule, all
surfaces above the normal ceiling height
(2.60 m) including the end walls should be
equipped with sound absorbers.
144

3/21/2022
7.INCLINED WALLS
Inclined walls have both a sound
spreading and sound concentrating
effect.
The sound spreading effect is achieved
by inclining the wall in proportion to
other walls and the ceiling. In general,
the walls inclined by more than 6
degrees ensure an excellent sound
diffusion. The most effective diffusion is
obtained by applying several angles.
145
8. VAULTED CEILING
In rooms with vaulted ceilings, the sound
is concentrated in the constructive centre
making the sound appear with a
stronger intensity. The sound movements
also appear stronger along the curve.
146
9. CONNECTED ROOMS
Rooms that are linked by a large
opening in between, influence each
others sound environment. A room
without acoustic regulation can act as an
echo chamber reinforcing the sound,
when connected to an acoustically
regulated room.
Both rooms must be equipped with sound
absorbers. If the distance between the
opening and the opposite walls is short
(5-6 m), the walls much be covered with
sound absorbers or diffusers.
147
10. ROOMS WITH MEZZANINE
In rooms with mezzanine, it is possible to create
different sound environments in the same room. In the
large, open room, an environment with long
reverberation time is created. The space above and
below the mezzanine has a shorter reverberation
time. The challenge posed in this type of rooms is the
sound reflection and the harmonization of the
different reverberation times.
The wall opposite the mezzanine should be
equipped with sound absorbers or diffusers. In
addition, sound absorbers should be placed on the
underside and the banister of the mezzanine. In
order to prevent large differences in the
reverberation times between the large room and the
space around the mezzanine, sound barriers can be
applied.
148

3/21/2022
21.02.2022
design of auditorium, conference hall, recording studio and
class rooms.
149
DESIGN OF AUDITORIUM
THE IMPORTANCE OF ACOUSTICS IN AN AUDITORIUM
Effective auditorium design should address
the following goals:
1. Speech, vocal performances and music
should all sound clear rather than distorted
or echoed.
2. Sounds should be loud enough for the
audience to hear, including those sitting at
the very back of the auditorium.
3. The right sounds should be isolated,
meaning performances and speeches ring
clearly over other sounds from the room.
151
DESIGN OF AUDITORIUM
THE FACTORS THAT AFFECT AUDITORIUM ACOUSTICS
Size of the Auditorium
In any room, size has an important influence on acoustics. Size includes the length, width and
height of the room. Larger and smaller auditoriums come with their own acoustical advantages.
For instance, a small room generally won’t allow music to ring out at richly as it will in a large
room. When it comes to volume, you’ll have an easier time getting the whole audience to hear
clearly in a small room, while a larger auditorium can pose some volume challenges. This is
why you need the other aspects of a large room to contribute to good acoustics and why you
need a quality sound system.
Another concern related to auditorium size is reverberation, which we’ll discuss more below.
Larger rooms can cause longer reverberation times, which can become excessive. Smaller
rooms can cause shorter reverberation times that may seem too short, making the room feel
acoustically “dead.”

3/21/2022
ECHO ELEMENATION
153
BACKGROUND NOISE ELEMINATION
154
ACOUSTIC SEATING AREA
155
RT
156

3/21/2022
157 158
EARLY REFLECTION
159 160

3/21/2022
161
28.02.2022
07.03.2022
14.03.2022
21.03.2022
162
163 164

3/21/2022
169 170
DESIGN OF CONFERENCE HALL
Room Shape: Volume
The ideal room volume per seat for lecture theatres is: Volume per seat = 5 m3
The lecture theatre at Bath University holds 350 people and has a volume of 1400
m3, this equates to 4 m3/seat, thus meeting the above criteria.
172

3/21/2022
Room Shape: Length
173
174
175
DESIGN OF RECORDING STUDIO
176
The acoustic behavior of acoustic spaces depends on a lot of different factors, including:
1. Type of wall/ceiling/floor construction (affects sound proofing and amount of sound reflected, so also the
reverb Time)
2. Room shape and proportions (affect the distribution of the resonance modes and diffusion)
3. Room size (affects the reverb time and the frequency of the resonance modes)
4. Choice of materials (affects the absorption factor, that usually varies across the frequency range)
5. Acoustic modules (can further affect the room acoustic adding absorption, reflection or diffusion).
6. Placement of speakers (main monitors, midfield, nearfield)
Properly designing small rooms (such as control rooms, sound booth, small live recording rooms) is more
difficult, as the strongest room resonance modes are usually in the critical bass frequency range (between 20
and 200 Hz) and can become a problem if the room proportions are not chosen properly. Also, because of the
small room size and relatively high frequency of the room modes, it is more difficult to achieve reverb
diffusion.

3/21/2022
DESIGN OF CLASSROOMS
177
Two things cause poor classroom acoustics: too much background noise and/or
too much reverberation.
Background noise is any sound that makes it hard to hear. In a classroom,
background noise can come from many places, including the following:
1. Sounds from outside the building, such as cars and lawnmowers
2. Sounds from inside the building, such as students talking in the hallway
3. Sounds from inside the classroom, such as air conditioning units and students
in the room
28.02.2022
Environmental noise and its control.
Lab: Introduction to sound level meter. Simple experiments to
predict RT, Background noise level and frequency analysis.
178
Environmental Noise and Control
Environmental noise is defined as unwanted or harmful outdoor sound created by human activity, such as noise emitted by
means of transport, road traffic, rail traffic, air traffic and industrial activity. Environmental noise is defined as unwanted or
harmful outdoor sound created by human activity, such as noise emitted by means of transport, road traffic, rail traffic, air traffic
and industrial activity.
Environmental noise constitutes a persistent threat created by dense and highly industrialized societies, from which one cannot
easily protect people in densely populated areas. Noise impacts on people reach from annoyance and sleep disturbance over
direct impacts on the aural system, indirect physical impacts to cognitive impairments and psychological disorders. Noise impacts
vary with exposure levels, time of day, sound source characteristics, peoples’ constitution, surrounding conditions and the cultural
settings and may well change over time.
It is estimated that a total of 2 billion citizens all over the world are subject to environmental – road traffic – noise levels of over
55 dB Lden, which are considered potentially harmful for their health.
Environmental noise is usually measured outdoors, near the façade of the building where noise exposure may be an issue.
Measurement height is specified in national and international standards. Popular measurement heights are 1.5 and 4 m,
respectively.
Environmental Noise and Control
Some common sources of environmental noise are:
1. Oil & Gas Drill Sites
2. Mines & quarries
3. Ports & harbors
4. Industrial/chemical plants
5. Power stations
6. Wind farms
7. Construction projects
The objective of environmental noise control is to improve the acoustic environment in a community by reducing noise levels. Noise
from sources such as industrial operations, aviation and rail, oil and gas extraction, and construction sites can affect neighboring
residential areas, ranging from intolerable noise levels to structural vibrations. Well planned noise control can eliminate a major
component of an industrial site’s impact on its surrounding environment.

Building services

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Building services

Similar to Building services (20)

Recently uploaded

Recently uploaded (20)

Building services