2. What is Sound?
A sound is any vibration (wave) traveling through the air or other
medium which can be heard when it reaches a persons ear.
• Sounds waves are:
• Longitudinal - oscillations parallel to propagation
• Mechanical - require a medium to travel through
3. How Sound is Created ?
• When an object vibrates, it creates sound – loud, deep and long, short and
high-pitched – pure, gravely, distorted, sweet, soft, piercing, buzz
• Any sound your ear can hear is created by the mechanical back-and-forth
motion of an object
4. Sound as a form of energy
• Sound energy is a form of energy associated with the
vibration of matter.
• The SI unit of sound energy is the joule (J).
• Sound is a mechanical wave and as such consists physically
in oscillatory elastic compression and in oscillatory
displacement of a fluid.
• Therefore, the medium acts as storage for both potential
and kinetic energy as well.
• Sound is the movement of energy through substances in
longitudinal (compression/rarefaction) waves. Sound is
produced when a force causes an object or substance to
vibrate — the energy is transferred through the substance
in a wave.Typically, the energy in sound is far less than
other forms of energy.
5. Compression
A compression is a region in a longitudinal wave where the
particles are closest together.
Rarefaction
A rarefaction is a region in a longitudinal wave where the
particles are furthest apart.
6. Velocity of sound
Def :The speed at which the sound waves travel or pass through any
medium is termed as as the sound velocity and it depends on the nature
and temperature of medium through which the sound travels
• The important facts to be remembered in connection with the
velocity of sound are as follows :
• The time required by sound waves to travel from one place to
another is quite appreciable
• The velocity of sound in air is affected by the amount of moisture in
the air the temperature of the air and the intensity of wind
• The velocity of sound is independent of the frequency or pitch of
sound
• It can be seen from table that sound travels much faster in solids and
liquids than it does in air
7. • Hearing range describes the range of frequencies
that can be heard by humans or other animals,
though it can also refer to the range of levels.
• The human range is commonly given as 20 to 20,000
Hz, though there is considerable variation between
individuals,
• especially at high frequencies, and a gradual loss of
sensitivity to higher frequencies with age is
considered normal.
• Sensitivity also varies with frequency,
Hearing range
8. • Echo is a reflection of sound that arrives at the
listener with a delay after the direct sound.
• The delay is proportional to the distance of the
reflecting surface from the source and the
listener.
• Typical examples are the echo produced by the
bottom of a well, by a building, or by the walls of
an enclosed room and an empty room.
• A true echo is a single reflection of the sound
source
EchoDecibles
• In acoustics to relate the intensity of sound to an intensity
level corresponding to the human hearing experience , the
“bell’’ unit named in honor of alexander graham bell was
introduced so that
• IL =log I/I0 (in bel)
• IL = 10 log I/Io( in decibles)
• Where IL= sound intensity level, decibles
• I= sound intensity watt per square centimeter
• Io = 1o raise to -16 watt / square cm
9. Amplitude & 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
Higher Amplitude Loud Lower Amplitude
Quiet Higher Amplitude Lower Amplitude Loud Quiet
10. Frequency and pitch
Pitch tells how high or low a sound is
– a higher pitch will have greater frequency (more
waves crammed into each second of time)
• higher frequencies have smaller wavelengths
Frequency – This is the number of oscillations per second.
This is represented with ‘f’ and measured in Hertz (Hz)
11. Wavelength of sound
This the distance between two pressure peaks or
valleys, measured in metres (m) and represented with
the Greek alphabet ‘l’ (lambda)
Period – This is the time taken for on complete oscillation.
This is measured in seconds(s) and represented with the
letter ‘T’.
Period
12. • 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.
Reflection
13. 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.
Absorption
14. 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.
Refraction
15. 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.
Diffusion
16. 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.
Diffraction
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.
Transmission
17. See some of the sound propagation principles given bellow;
The propagation of sound energy through a media via sound waves i.e. compression and rarefaction of
sound waves.
The propagation of sound depends up on the frequency of sound source and the capacity of listener ear
drum.
The propagation of sound depends up on the weather conditions like air temperature, presence of
moisture, air velocity etc.
The propagation of sound depends up on the topographical features like ground cover, hills and obstacles
between the source and receivers, type of space like open or closed.
When sound is generated in a place, it can move or spread in
all direction by air is called as propagation of sound. Sound can
propagate for origin to in all directions like a person blowing up
a balloon with his moth.
Propagation of Sound:
