1. Sound
• Sound, any disturbance that travels through
an elastic medium such as air, ground, or
water to be heard by the human ear.
• Sound is a vibration that propagates as a
mechanical wave of pressure and
displacement, through some medium (such as
air or water)
2. Sound waves are generated by any vibrating body.
For example, when a violin string vibrates upon being
pluck, its movement in one direction pushes the
molecules of the air before it, crowding them
together in its path.
When it moves back again past its original position
and on to the other side, it leaves behind it a nearly
empty space, i.e., a space with relatively few
molecules in it.
Generation of Sound Waves
3. In other words, the vibratory motion set up by the violin string
causes alternately in a given space a crowding together of the
molecules of air (a condensation) and a thinning out of the
molecules (a rarefaction).
Taken together a condensation and a rarefaction make up a
sound wave; such a wave is called longitudinal, or
compressional, because the vibratory motion is forward and
backward along the direction that the wave is following.
Because such a wave travels by disturbing the particles of a
material medium, sound waves cannot travel through a
vacuum.
Generation of Sound Waves
6. Propagation of sound
• Sound propagates through compressible media such as
air, water and solids as longitudinal waves and also as a
transverse waves in solids .
• The sound waves are generated by a sound source,
such as the vibrating diaphragm of a stereo speaker.
The sound source creates vibrations in the surrounding
medium. As the source continues to vibrate the
medium, the vibrations propagate away from the
source at the speed of sound, thus forming the sound
wave.
• During propagation, waves can be reflected, refracted,
or attenuated by the medium
7. Sound waves
• Sound is transmitted through gases, plasma, and
liquids as longitudinal waves, also called compression
waves.
• Through solids, however, it can be transmitted as both
longitudinal waves and transverse waves.
• Longitudinal sound waves are waves of alternating
pressure deviations from the equilibrium pressure,
causing local regions of compression and rarefaction,
• transverse waves (in solids) are waves of alternating
shear stress at right angle to the direction of
propagation.
13. Amplitude-
is the maximum distance
the particles in a wave
vibrate from their rest positions.
Frequency
- the number of waves
produced in a given time
14. Sounds are generally audible to the human ear if their
frequency (number of vibrations per second) lies between 20
and 20,000 vibrations per second (20 Hz-20 kHz), but the
range varies considerably with the individual.
Sound waves with frequencies less than those of audible
waves are called infrasonic;
those with frequencies above the audible range are called
ultrasonic
Characteristics of Sound Waves
15. The velocity of sound is not constant, however, for it varies in
different media and in the same medium at different
temperatures.
For example, in air at 0°C. it is approximately 1,089 ft per
second
but at 20°C it is increased to about 1,130 ft per second, or an
increase of about 2 ft per second for every centigrade degree
rise in temperature.
Characteristics of Sound Waves
16. Sound travels more slowly in gases than in liquids, and more
slowly in liquids than in solids.
Since the ability to conduct sound is dependent on the
density of the medium, solids are better conductors than
liquids, liquids are better conductors than gases.
Velocity of sound in some medium are;
A. Air 344 m/s
B. Water 1410 m/s
C. Muscles 1540 m/s
Characteristics of Sound Waves
17. Sound waves can be reflected, refracted (or bent), and
absorbed as light waves can be.
The reflection of sound waves can result in an echo
A sound wave can be reinforced with waves from a body
having the same frequency of vibration, but the combination
of waves of different frequencies of vibration may produce
“beats” or pulsations.
Characteristics of Sound Waves
18. Speed of Sound
• Velocity(v) of a wave= Frequency (f) times the
wavelength (l)
• V = fl
• The speed of propagation of sound in dry
air at a temperature of 0° C (32° F) is
331.6 m/sec (1088 ft/sec). If the
temperature is increased, the speed of
sound increases; thus, at 20° C (68° F),
the velocity of sound is 344 m/sec (1129
ft/sec)
19. Ultrasound
- sound waves with frequencies above the
normal human range of hearing.
Sounds in the range from 20-100kHz
Infrasound
- sounds with frequencies below the
normal human range of hearing.
Sounds in the 20-200 Hz range
20. Sound interference
• When two or more sound waves from
different sources are present at the same
time, they interact with each other to produce
a new wave. The new wave is the sum of all
the different waves. Wave interaction is called
interference..
22. Constructive interference
• If the compressions and the rarefactions of
the two waves line up, they strengthen each
other and create a wave with a higher
intensity. This type of interference is known as
constructive
23. Destructive interference
• When the compressions and rarefactions are out of
phase, their interaction creates a wave with a
dampened or lower intensity. This is destructive
interference. When waves are interfering with each
other destructively, the sound is louder in some
places and softer in others. As a result, we hear
pulses or beats in the sound.
24. • Dead spots
Waves can interfere so destructively with one
another that they produce dead spots, or places
where no sound at all can be heard. Dead spots
occur when the compressions of one wave line
up with the rarefactions from another wave and
cancel each other
25. Refraction of sound waves
• sound travels faster in some materials than others.
• Sound waves travel outward in straight lines from their
source until something interferes with their path.
• When sound changes mediums (enters a different material)
at an angle other that 90 degrees, it is bent from its original
direction. This change in angle of direction is called
refraction.
• Because of the angle, part of the wave enters the new
medium first and changes speed. The difference in speeds
causes the wave to bend.
• The velocity of sound in each material is determined by the
material properties (elastic modulus and density) for that
material.
26. • when the wave encounters the interface between
these two materials, the portion of the wave in the
second material is moving faster than the portion of
the wave in the first material. It can be seen that this
causes the wave to bend.
27. • The angle of refraction depends on the angle that the waves has when it
enters the new medium and the velocities of the waves in the two
materials. Snell's Law describes the relationship between the angles and
the velocities of the waves. Snell's law equates the ratio of material
velocities V1 and V2 to the ratio of the sine's of incident (Q1) and
refracted (Q2) angles, as shown in the following equation
28. Reflection of sound waves
• When sound travels in a given medium, it strikes the surface
of another medium and bounces back in some other
direction, this phenomenon is called the reflection of sound.
• The waves are called the incident and reflected sound waves.
29. • The sound waves that travel towards the
reflecting surface are called the incident
sound waves. The sound waves bouncing back
from the reflecting surface are called reflected
sound waves.
• Law of Reflection: The angle of incidence is
equal to the angle of reflection.
30. Intensity of sound
• Rate of energy flow or power carried by sound
per unit area.
• Unit watt/m2
Decibel is the unit of sound. Its symbol is ‘dB’.
We can define decibel as
A unit of measurement used to express the
ratio of one value of a power or field quantity to
another on a logarithmic scale, the logarithmic
quantity being called the power level or field
level, respectively
31. Decibel formula
• Formulas to Calculate Decibel
• The calculation of decibel can be done when power is
given as well as when current and voltage are given.
• When power is given:
• The most basic form for decibel calculations is given
below:
• NdB=10log10(P2/P1)
32. Noise Level Chart (Decibel Chart)
Decibel Sound Source
10 Almost inaudible Normal breathing
20 Audible Rustling leaves, Mosquitoes
30 Very quiet Whisper
40 Quiet
Stream, Refrigerator
humming
50 Limited Sound Quiet office
55 Normal Sound Filtering Coffee maker
60 Fairly Quiet Normal conversation
70 Irritating Vacuum cleaner, Hairdryer
75 Constant Sound Dishwasher
80 Unpleasant City traffic noise
33. • Some common sounds and their intensity in decibels are as follows:
• Near complete silence: 0 dB
• Normal conversation: 60 dB
• Whisper: 15 dB
• Library: 45 dB
• Heavy city traffic: 85 dB
• Baby crying: 110 dB
• MP3 player at maximum volume: 105 dB
• Toilet flushing: 75-85 dB
• Balloon popping: 157 dB
• Noisy restaurant: 90 dB
• Concerts: 120 dB
• Jet engine: 120 dB
