The document discusses various topics related to architectural acoustics including: - The definition of architectural acoustics as the study of sound generation, propagation, and transmission in buildings. - The importance of applying acoustic principles to improve quality of life through work and leisure environments. - The need to both enhance desirable sounds like music, while reducing undesirable noise.

2. 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
life at work, during leisure time and in the home.
• Some sounds are desirable and 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).

3. • A science that deals with the production, control,
transmission, reception, and effects of sound.”
• Sound is reflected, transmitted, or absorbed by
the materials it encounters.
• Soft surfaces, such as textiles, and batt insulation,
tend to absorb sound waves, preventing them
from further motion.
• Hard surfaces, such as ceramic tile, gypsum board,
or wood, tend to reflect sound waves, causing
‘echo’. Reverberation is the term used to describe
sound waves that are reflected off of surfaces.
• Dense, massive, materials, such as concrete or
brick, tend to transmit sound waves through the
material.
ACOUSTICS
Place People
Activity

4. 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.
• Sound is a vibration that propagates as a typically audible mechanical wave of
pressure and displacement, through a medium such as air or water
SOUND

5. • Consists of alternate compressions and
rarefactions that are set up vibrating
body
• Sound waves transmits or travels in all
directions through any medium
whether solid liquid or gas.
• The average sound travels in air at
ordinary temperatures and pressure
with a speed of 340m/sec.
• Sound cannot travel by vacuum.
• Wavelength is the distance between any
two consecutive points on a wave.
Frequency is the number of cycles of
vibration per second, therefore
Characteristics of sound

6. • Sound waves travel into the ear canal until they reach the eardrum. the eardrum
passes the vibrations through the middle ear bones or ossicies into the inner ear. The
inner ear is shaped like a snail and is also called the cochlea
• Inside the cochlea there are thousands of tiny hair cells change the vibrations into
electrical signals that are sent to the brain through the hearing nerve. The brain tells
you that you are hearing a sound
How do we Hear Sound ?

7. • Acoustics is defined as the scientific study of sound which includes the effect of
reflection, refraction, absorption diffraction and interference. It also deals with the
properties of the sound waves, their origin, propagation and their action on obstacles.
What is acoustics ?
What is Sound ?
• Sound is an alteration of pressure that propagates through an elastic medium such as
air which produces and auditory.
Why we need acoustic ?
• Acoustics are fundamentally important to learning environments. Learning is
intrinsically linked with communication, and aural {sound) communication is
acoustics. Similarly, learning is concentration, and external noise is a major distracting
factor in education.
• The importance Of acoustics is not limited to classroom. Noise corridors arid public
space can soar if they are too reverberant (too much echo), with voices raised louder
and louder. overcome the background echo. just like shouting conversations at a noisy
cocktail party or restaurant. So to come over this problems sounds we need acoustics.

8. How is Sound Measured?
• Sound energy travels in waves and is measured in frequency and amplitude.
• Amplitude measures how forceful the wave is. it is measured decibels or dBA of
sound pressure. 0 d3A is the softest level that a person can hear. Normal speaking
voices are around 65 dBA, concert can be about 120 dBA
• Frequently is measured in the number of sound vibration in one second. A healthy ear
can hear seconds of very low frequency, 20 Hertz ( or 20 cycles per second). To a very
high frequency of 20,000 Hertz. The lowest A key on the piano is 27 Hertz. The middle
C key on a PIANO CREATER A 262 Hertz tone. The highest key on the piano is 4186
Hertz

9. How is Sound Measured?
• Sound energy travels in waves and is measured in frequency and amplitude.
• Amplitude measures how forceful the wave is. it is measured decibels or dBA of
sound pressure. 0 d3A is the softest level that a person can hear. Normal speaking
voices are around 65 dBA, concert can be about 120 dBA
• Frequently is measured in the number of sound vibration in one second. A healthy ear
can hear seconds of very low frequency, 20 Hertz ( or 20 cycles per second). To a very
high frequency of 20,000 Hertz. The lowest A key on the piano is 27 Hertz. The middle
C key on a PIANO CREATER A 262 Hertz tone. The highest key on the piano is 4186
Hertz
Sound
Two different units for expressing the energy of
sound is employed.
1. The intensity of sound is expressed in decibel.
2. Phon is the unit used for measuring the
loudness sensation in the ear.

10. Terminology related to acoustics
• AIRBORNE NOISE: Noise that arrives at a point of interest by propagation through the
air.
• AIRBORNE SOUND: Sound that reaches the point of interest by propagation through
the air.
• AMBIENT NOISE/SOUND: Noise level in a space from all sources such as HVAC or
extraneous sounds from outside the space. Masking sound or low-level background
music can contribute to the ambient level of sound or noise.
• BACKGROUND NOISE: The sum total of all noise generated from all direct and
reflected sound sources in a space that can represent an interface to good listening
and speech intelligibility. (Hearing-impaired persons are especially victimized by
background noise).
• DECIBEL (dB): Sound level in decibels as a logarithmic ratio. Sound intensity described
in decibels. i.e.:
• Breathing – 5 dB
• Office Activity – 50 dB
• Jet Aircraft During Takeoff at 300′ Distance – 130 dB
• DEFLECTION: The distance an elastic body or spring moves when subjected to a static
or dynamic force. Typical units are inches or mm.

11. • DIFFUSION: The scattering or random reflection of a sound wave from a surface. The
directions of reflected sound is changed so that listeners may have a sensation of
sound coming from all directions at equal levels.
• EARLY DECAY TIME: This is derived from the reverberation time decay curve, typically
between 0 dB and 10 dB below the initial level. A good indicator of speech clarity is a
short EDT.
• EFFECTIVE LEVEL: Also known as the average level, it is the root mean square of the
instantaneous level over a given period of time.
• FREQUENCY: The number of oscillations or cycles per unit of time. Acoustical
frequency is usually expressed in units of Hertz (Hz) where one Hz is equal to one
cycle per second.
• FREQUENCY ANALYSIS: An analysis of sound to determine the character of the sound
by determining the amount of sounds at various frequencies that make up the overall
sound spectrum. i.e.: Higher Frequency Sound or Pitch vs. Low Frequency
• NOISE: Unwanted sound that is annoying or interferes with listening. Not all noise
needs to be excessively loud to represent an annoyance or interference.
• NOISE REDUCTION (NR): The amount of noise that is reduced through the
introduction of sound absorbing materials. The level (in decibels) of sound is reduced
on a logarithmic basis.

12. • REFLECTION: The amount of sound wave energy (sound) that is reflected off a
surface. Hard non-porous surfaces reflect more sound than soft-porous surfaces.
Some sound reflection can enhance the quality of signal of speech and music. (See
Echo).
• REVERBERATION TIME: Sound after it is ended at the source will continue to reflect
off surfaces until the sound wave loses energy by absorption to eventually die out.
• SABIN: A unit of sound absorption based on one square foot of material. Baffles are
frequently described as providing X number of sabins of absorption based on the size
of the panel tested, through the standard range of frequencies 125-4000 Hz. The
number of sabins developed by other acoustical materials are determined by the
amount of material used and its absorption coefficients.
• SOUND ABSORPTION: The property possessed by materials, objects and air to
convert sound energy into heat. Sound waves reflected by a surface causes a loss of
energy. That energy not reflected is called its absorption coefficient.
• SOUND PRESSURE LEVEL: The sound pressure level, in decibels, of a sound is 20 times
the logarithm to the base 10 of the ratio of the sound pressure to the reference
pressure. The reference pressure shall be explicitly stated and is defined by standards.
• SOUNDPROOFING: Building materials that make structures impervious to sound or
insulates against sound

13. Absorption: When sound waves hit the surface of an obstacle, some of its energy is
reflected while some are lost through its transfer to the molecules of the barrier.
Refraction : This is the bending of sound when it travels from one medium into another
medium
Diffraction: When the wavelength of a sound wave is smaller or equal to the size of the
obstacle
Transmission: In this phenomenon, sound wave is carried by molecules of the obstacle
through vibration and reemitted

14. SOUND IN CLOSED SPACES
• In case of concave shaped reflecting interior surface or domed ceiling or an enclosure,
depending upon the curvature of these surfaces, there is possibility of meeting the
sound rays at appoint called as sound foci and thus it creates the sound of large
intensity .
• This defect can be minimized by providing proper geometrical design.
• Shape of the interior faces including ceiling and also by providing absorbent materials
on focusing areas.
• On encountering barriers posed by the enclosure, sound waves are likely to behave in
the following ways:
• Reflection
• Absorption
• Refraction
• Diffusion
• Diffraction

16. SOUND IN OPEN SPACES
• Near field : The near field of a source is the region close to a source where the sound
pressure level may very significantly with a small change. In this region the sound field
does not decrease by 6 dB each time the distance from the source is increased (as it
does in the far field).
• Far field : The far field of a source begins where the near field ends and extends to
infinity. Note that the transition from near to far field is gradual in the transition
region. It is divided into two fields:
• Free field : The free field is a region in space where sound may propagate free from
any form of obstruction or reflecting surfaces.
• Reverberant field : The reverberant field of a source is defined as that part of the
sound field radiated by a source which has experienced at least one reflection from a
boundary of the room or enclosure containing the source.

17. ABSORPTION COEFFICIENT
• Sound absorbed by surface and transmitted through the surfaces are considered
together as being absorbed and are represented by A.C
a = Sound energy absorbed
Total energy per unit area
• If absorption coefficient of material is 0.5 then it shows that 50% of energy is
absorbed by it per unit area.
• The loss of sound energy is absorbed by the material . This is because of conversion
into heat due to frictional resistance inside the pores of material.
• The fibrous and porous nature of material contribute to their sound absorbing
capacity.
• The value of absorption coefficient depends upon the nature of material and the
frequency of sound.
• Greater the frequency ,larger is the value of the coefficient in the same material.

18. BEHAVIOR OF SOUND
Sound intensity level:
The sound intensity is given as,Where, P is the sound power,
A is the area , To measure Sound intensity level we compare the given sound intensity
with the standard intensity.
I=P/A
Sound Intensity Level Formula is given by,
Where I = sound intensity and
Io = reference intensity It is expressed in decibels (dB).
Sound Intensity Formula is used to determine the intensity of sound waves. The S.I unit of
sound intensity is Watt per meter square (W/m2)
• A sound intensity level, LI , may be defined as follows:
• LI =10 log10 (sound intensity)
(ref. sound intensity)

19. INVERSE SQUARE LAW
• The Inverse Square Law teaches us that for every doubling of the distance from the
sound source in a free field situation, the sound intensity will diminish by 6 decibels.
• As a sound wave propagates spherically, the sound energy is distributed over the
ever-increasing surface diameter of the wave front surface.
• Under ideal conditions a free field could be represented by a sound signal being
generated from a mountain peak. In real life situations however, rooms bounded by
walls, floors and ceilings will interrupt the inverse square law at a distance in tan
average 30′ square room at approximately 10-12 feet from the sound source.
• Nevertheless it is important to accept the notion that sound will diminish in intensity
with distance. For example, in a typical classroom with a teachers voice signal of 65
decibels at a three-foot distance from the teacher; at 6 feet away the sound intensity
will be 61 decibels and at twelve feet it will diminish down to 54 decibels. (This is
important to remember as we discuss the Signal to Noise Ratio S/NR later on)

20. INVERSE SQUARE LAW

21. DOPPLER EFFECT
• So far, we have only considered stationary sources of sound and stationary listeners
(or observers). However, if either the source or the observer is moving, things change.
This is called the Doppler effect.
• Objects of interest may be the speed of a car on the highway, the motion of blood
flowing through an artery
• One of the most common examples is that of the pitch of a siren on an ambulance or
a fire engine. You may have noticed that as a fast moving siren passes by you, the
pitch of the siren abruptly drops in pitch. At first, the siren is coming towards you,
when the pitch is higher. After passing you, the siren is going away from you and the
pitch is lower. This is a manifestation of the Doppler effect

22. DOPPLER EFFECT
• You hear the high pitch of the siren of the approaching ambulance, and notice that its
pitch drops suddenly as the ambulance passes you. That is called the Doppler effect

23. DOPPLER EFFECT

24. REQUIREMENT AND CONDITIONS FOR GOOD ACOUSTIC
• The initial sound should of adequate intensity such that it can be heard throughout
the hall.
• The sound produced should be evenly distributed over the entire area covered by the
audience.
• In the hall used for speech, the initial sound should be clear and distinct.
• In the hall used for music and dance the initial sound should reach the audience with
the same frequency and intensity .
• All noises whether originating from inside or outside of the hall should be reduced to
such an extent that they don’t interfere with the normal hearing of music.

25. ACOUSTIC MATERIALS
Sound diffusers
• Quadra pyramid diffusers
• Pyramid diffuser
• Quadratic diffuser
• Double duty diffuser
Noise barriers
• Vibration control
• Composite
Sound
reflectors/
isolators
Sound absorbers
• Wall panels
• Ceiling clouds
• Ceiling tiles
• Ceiling baffle
• Broadband baffle
• absorbers
ACOUSTIC MATERIALS

26. SOUND ABSORBERS
• These materials eliminate sound reflections and are
generally porous, with many pathways that redirect sound
and cause it to lose energy.
• Typical sound absorbing materials are fiberglass, rock wool,
open cell polyurethane foam, cellular melamine foam,
heavy curtain blankets and thick fabric wall coverings.
• Absorber materials do not substantially block sound, but
absorption can enhance isolation by stopping air
movement that would otherwise allow sound and noise to
travel.
SOUND DIFFUSERS. (ALT. DIFFUSORS.)
• These devices reduce the intensity of sound by scattering it
over an expanded area, rather than eliminating the sound
reflections as an absorber would.
• Traditional spatial diffusers, such as the polycylindrical
(barrel) shapes also double as low frequency traps.
SOUND DIFFUSERS
SOUND ABSORBERS

27. NOISE BARRIERS
• These materials are heavy, dense and massive to prevent sound
penetration.
• A common material is drywall (gypsum, sheetrock). Thin
materials with high sound blocking characteristics are lead foil
and mass loaded vinyl.
• A sandwich of dissimilar materials such as five-eighths inch
gypsum, one- eighth inch vinyl barrier, and a half- inch finish
layer of drywall will block more effectively than an equivalent
thickness of drywall alone.
• More energy is lost as sound must change its speed for each
different material
SOUND ISOLATORS.
• These devices are resilient and prevent sound transmission
through the structural steel or concrete of a building as well as
its plumbing and air handling systems.
• Typical devices are resilient channel for drywall, isolation pads
for floors, and special adhesives for walls to avoid the hard
connections of nails and screws that often provide a sound path
through otherwise effective sound insulation materials.
SOUND ISOLATORS.
NOISE BARRIERS

28. STUDY OF VARIOUS ABSORBING MATERIALS
• All materials should absorb sound but some to a lesser extent.
• Sound wave strikes porous surface and dissipate heat channels.
• Efficiency of sound energy depends upon the porosity of material.
• Absorption coefficient is used to express the amount of incident sound that can be
absorbed .
THE NEED FOR ABSORBING MATERIALS
• To ensure Privacy
• Noise control
• To improve Environment for efficient working.