WHAT IS ACOUSTICS? what is sound? AMPLITUDE AND VOLUME, FREQUENCY AND PITCH LOUDNESS OR INTENSITY LOUDNESS OR INTENSITY LOUDNESS OR INTENSITY, TIMBRE VELOCITY OF SOUND AMPLITUDE REFLECTION

1. INTRODUCTION
WHAT IS ACOUSTICS ?
•Acoustics is a branch of physics that study the sound.
•Acoustics concerned with the production , control ,transmission and
effect of sound.
•The study of acoustics has been fundamental to many developments
in the arts, science,technology,music,biology etc.

2. •Sound can be described as a disturbance or turbulance which passes through a
physical medium in the form of longitudinal waves from a source to a receiver
causing a sensation of hearing.
•This medium will be solid , fluid or gas.
•The speed of sound through these different media differs due to their molecular
composition.
IN SIMPLE DEFINITION
•A Sound is any vibration (wave) travelling through the air or other medium which
can be heard when it reaches a persons ear .
WHAT IS SOUND

3. AMPLITUDE AND VOLUME
• The amplitude of a wave determines a sounds volume.
– Volume tells how loud or soft a sound is :-
• Determined by how much energy a wave carries.
– Amplitude describes how much energy a wave is carrying :
• more energy = greater amplitude = louder sound.
• greater amplitude = taller wave or more intense compressions.

4. DECIBELS & SOUND VOLUME
Audible sound energy is measured in decibels (dB)
– Only measures within the limits of human hearing
• 0 is just barely audible
• 120+ causes pain/damage
Hearing damage depends on:
– sound amplitude (loudness) .
– frequency (pitch) of the sound .
– duration of exposure to the sound .

5. FREQUENCY AND PITCH
• PITCH-highness or lowness of a sound.
• FREQUENCY-number of sound waves that passes through a point in a
certain amount of time such as one second.
• The greater the frequency the higher the pitch.
• All sound waves are travelling at about the same speed .So waves with
a shorter wavelength arrive (at your ear, for example) more often
(frequently) than longer waves.
• Hertz (Hz)- unit to measure frequency and pitch.
• Spoken words have frequency band of 170 Hz to 4000 Hz.
• Natural musical instruments have frequency band of 50 Hz to 8500 Hz.

6. LOUDNESS OR INTENSITY
• Description of how high or low the sound seems to a Loudness is a
psychoacoustic property of sound, in that it represents our human perception
of how “loud” or “soft” sounds of various intensities are.
• Units of measurement include the phon and sone .
• Intensity is an acoustic property of sound that can be physically measured .
• Unit of measure is the decibel (dB)
TIMBRE
• Timbre is composed of the whole spectrum of sound— not just the pitch.
• It is what differentiates musical instruments.
• A trumpet, a piano, and a flute each produce a pitch of
• On the musical scale; however, each sounds differently due to its timbre.

7. • In other words, if a flute plays a note, and then a violin plays the same
note, for the same length of time, at the same loudness, we can still easily
distinguish between the two sounds.
• This difference is in the timbre of the sounds. This is due to the variation in
the spectral characteristics of the sound.
VELOCITY OF SOUND
This is the rate at which a sound wave travels from a source through a
medium to the receiver. The unit is m/s.
AMPLITUDE
This is the distance between a crest (the highest point) and a valley (the
lowest point)

8. BEHAVIOUR OF SOUND ENCLOSURES :
An enclosed space is a room or area bounded on every of its sides.
The materials for enclosure may be classified into two:
Those that allow sound rays to pass through and
Those that do not allow sound rays to pass through. On encountering barriers posed
by the enclosure, sound waves are likely to behave in the following ways:
•Reflection
•Absorption
• Refraction
• Diffusion
• Diffraction
• Transmission

9. REFLECTION
•This occurs when the wavelength of a sound wave is smaller than the surface of an
obstacle. In the case of an enclosed space, the sound waves hit every side of the
enclosure continuously until the sound energy reduces to zero.
•The amount of waves reflected depends on the smoothness, size, and softness of
the materials of enclosure. The angle of incidence of sound rays is equal to that of
the reflected rays only if the surface of the reflector is flat. But when it is curved,
the angles are different.

10. 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.
•The lost sound energy is said to have been absorbed by
the barrier.
•The thickness and nature of the material as regards its
softness and hardness influences the amount of sound
energy absorbed.

11. REFRACTION
• This is the bending of sound when it travels from one
medium into another medium.
• The difference in the composition of the two different
media bends the sound
• i.e. the angle of incidence changes into an angle of
refraction as it travels into the new medium.

12. DIFFUSION
• This is the scattering of waves from a surface.
• It occurs as a result of the texture and hardness of the obstacle is
comparable to the wavelength of the sound.
• The direction of the incident ray changes when it strikes the
surface of the obstacle.
• Satisfaction is achieved when sound is heard in all direction at
equal level.

13. DIFFRACTION
When the wavelength of a sound wave is smaller or equal to the
size of the obstacle, the sound rays tend to bend round the edge of
the obstacle thereby turning the edge to a sound source.

14. TRANSMISSION
In this phenomenon, sound wave is carried by molecules of the
obstacle through vibration and re-emitted at the other side
irrespective of the medium. It can be structure borne, air borne or
impact sound.

15. COMMON ACOUSTICAL DEFECTS
Acoustical conditions in a big room, hall or auditorium etc`. Are
achieved when there is clarity of sound in every part of occupied
space.
For this, the sound should rise to suitable intensity everywhere
with no echoes or near echoes or distortion of the original sound ;
with correct reverberation time.
COMMON DEFECTS :
(1) Reverberation
(2) Formation of echoes
(3) Sound foci
(4) Dead spots
(5) Insufficient loudness
(6) External noise

16. REVERBERATION
• Reverberation is the persistence of sound in the enclosed space , after
the source of sound has stopped.
• Reverberant sound is the reflected sound , as a result of improper
absorption.
• Reverberation may results in confusion with the sound created next.
• However some reverberation is essential for improving quality
sound.
• The time during which the sound persists is called the reverberation
time of sound in the hall.
As per Prof. W .C. Sabins reverberation time ‘t’ is given by formula
t= 0.16 V /A where V=volume of room in cubic meters
A= total absorbing power of all the
surfaces of room/ hall.

17. REMEDIES
• The reverberation time can be controlled by the suitable choice of
building materials and furnishing materials.
• Since open windows allow the sound energy to flow out of the hall,
there should be a limited number of windows. They may be opened or
closed to obtain optimum reverberation time.
ECHO'S
• Not all sound that hits matter is absorbed. Some of it is
reflected. That means sound bounces off the solid matter
the way a tennis ball bounces off a wall. Sound reflected
back to its source is an echo.
• An echo is produced when the reflected sound wave
reaches the ear just when the original sound from the
same source has been already heard.
• Thus there is repetition of sound.
• The sensation of sound persists for 1/10th of a second after
the source has ceased.
• Thus an echo must reach after 1/10th second of the direct
sound

18. • Multiple echoes may be heard when a sound is reflected from a number of
reflecting surfaces placed suitably.
• This defect can be removed by selecting proper shape of the hall .
• And by providing rough and porous interior surfaces to disperse the energy of
echoes.
REMEDIES
• This defect is avoided by selecting proper shape for the auditorium. Use
of splayed side walls instead of parallel walls greatly reduces the
problem and enhance the acoustical quality of the hall.
• Echoes may be avoided by covering the opposite walls and high ceiling
with absorptive material.

19. SOUND FOCI
• This defect is the out come of formation of sound foci.
• Because of high concentration of reflected sound at sound foci , there is deficiency
of related sound at some other points.
• These spots are known as dead spots where sound intensity is so low that it is
insufficient for hearing.
REMEDIES
• This defect can be removed by suitably placing diffusers and reflectors.
• Right proportions of internal spaces.
• Geometrical shape of roof helps in proper distribution of sound

20. EXTERNAL NOISE
• External noises from vehicles , traffic engines , factories , machines etc. may enter
the hall either through the openings or even through walls and other structural
elements having improper sound insulation.
REMEDIES
• This defect can be removed by proper planning of the hall with respect to its
surroundings and by proper sound insulation of external walls.
SOUND SHADOWS
• An acoustic shadow or sound shadow is an area through which sound waves fail to
propagate, due to topographical obstructions or disruption of the waves via
phenomena such as wind currents, buildings, or sound barriers.
RESONANCE
• Resonance occurs due to the matching of frequency. if the window panels and
sections of wooden portions have not been tightly fitted, they may start vibrating,
thereby creating an extra sound in addition to the sound produced in the hall or
room.

21. REMEDY
• The resonance may be avoided by fixing the window panels
properly. any other vibrating object which may produce
resonance ban be placed over a suitable sound absorbing
material.
LOUDNESS
• The unifirm distribution of loudness in a hall or a room is an important
factor for satisfactory hearing. sometimes, the loudness may get reduced
due to excess of sound- absorbing materials in a hall or a room.
REMEDIES
If the loudness of sound is not adequate, the loudness can be increased by
adopting the following methods.
• by using suitable absorbants at place where noise is high. as a result, the
distribution of loudness may become uniform.
• by constructing low ceiling for the reflection of sound towards the listener.
• by using large sounding boards behind the speaker and facing the audience.
• by using public adress system like loudspeakers.

22. NOISE
• Noise is unwanted sound which masks the satisfactory hearing of
speech and music.
• There are mainly three types of noises that are to be minimized.
• They are (i) air-borne noise,
(ii) structure-borne noise and
(iii) internal noise.
AIR BORNE NOISE
• The noise that comes into building through air from distant sources is
called air-borne noise.
• A part of it directly enters the hall through the open windows, doors or
other openings while another part enters by transmission through walls
and floors.
REMEDIES
• The building may be located on quite sites away from heavy traffic, market
places, railway stations, airports etc.
• They may be shaded from noise by interposing a buffer zone of trees, gardens
etc.

23. STRUCTURE-BORNE NOISE
• The noise which comes from impact sources on the structural extents
of the building is known- as the structure-borne noise. It is directly
transmitted to the building by vibrations in the structure. The common
sources of this type of noise are foot-steps, moving of furniture,
operating machinery etc.
REMEDIES
• The problem due to machinery and domestic appliances can be
overcome by placing vibration isolators between machines and their
supports.
• Cavity walls, compound walls may be used to increase the noise
transmission loss.

24. INTERNAL NOISE
• Internal noise is the noise produced in the hall or office etc.
• They are produced by air conditioners, movement of people etc.
REMEDIES
• The walls, floors and ceilings may be provided with enough
sound absorbing materials.
• The gadgets or machinery should be placed on sound absorbent
material.
SOURCES OF INDOOR AND OUTDOOR NOISES

25. When designing a home, locate noise-sensitive rooms such as studies and
bedrooms away from noisy activity spaces such as the laundry and garage,
and away from sources of external noise such as roads. The least noise-
sensitive space such as the garage and laundry can be located closer to
source of noise where they will also provide a buffer zone. Internal wall may
also be constructed using a proprietary acoustic wall construction system
utilising double studs, resilient channels, multiple layers of linings and sound
absorbing insulation.
Zoning in most easily achieved with new houses, but it may be possible to
re-allocate rooms or make suitable alterations in existing houses. When
you’re considering zoning for noise, you must also consider orientation for
sun, views and wind.

26. Acoustical Site Planning
Many site planning techniques can be employed to shield a residential development
from noise. These can include:
• Increasing the distance between the noise source and the receiver;
• placing nonresidential land uses such as parking lots, maintenance facilities, and
utility areas between the source and the receiver;
• locating barrier-type buildings parallel to the noise source or the highway; and
• orienting the residences away from the noise.