This document provides an overview of acoustics and related topics. It defines acoustics as the science of sound, including its generation, transmission, and reception. Acoustics is related to various fields such as engineering, arts, life sciences, and earth sciences. The document discusses sound waves, factors that affect the speed of sound, types of waves, units used to measure sound such as decibels, interference and standing waves, and the Doppler effect. The course will cover additional topics such as sound intensity, environmental acoustics, electro-acoustics, and underwater acoustics.

1. ACOUSTICS
EC522
Dr. Mohamed Ismail
Lecture (1)

2. Acoustics
 It is known as the science of sound including three
process:
(I) Generation (Production).
(II) Transmission
(III) Reception.
Acoustics is related to different branches as follows:
[1] Engineering: (i) Mechanical Engineering (vibration – noise).
(ii) Electrical Engineering: Electro-acoustics.
(iii) Material Engineering.
[2] Arts: (i) Architecture, such as theater.
(ii) Music Instruments.
[3] Life Science: (i) Medicine (i.e. UI=Ultrasonic Imaging).
Note: In biology, this science is called
Bioacoustics.

3. (ii) Psychology: Leading to reduction of concentration
and an aggressive behavior.
(iii) Physiology: Affecting upon some of human's body
systems (i.e. Cardiac system and hearing system).
[4] Earth Science: (i) Underwater acoustics.
(ii) Forecasting (acoustic antenna).
(iii) Seismic acoustics.
Acoustics (Cont.)

4. Course Contents
Introduction of acoustics, acoustic wave
equation and its solution.
Chapter One
Sound intensity, power, energy, density
level and loudness.
Chapter Two
Environmental acoustics.
Chapter Three
Electro-acoustics
Chapter Four
Underwater acoustics
Chapter Five

5.  What is the definition of sound?
Sound is generated by the mechanical disturbance of the
medium’s particles. It is found that the particles near the
source of sound vibrate back and forth and due to the
elastic collision between particles, the sound propagates.
 Factors affecting speed of sound
Temperature: Sound moves through hot air faster than
cold air due to the increased speed of the particles.
Type of medium or medium characteristic: Sound
moves well through dense material and material that
returns quickly to its original position. Thus, sound moves
fastest in a solid and slowest in a gas.
Chapter One

6. Reason
 Sound travels more quickly through solids and liquids
because the individual molecules are closer together than the
molecules in gas.
 Sound waves CANNOT move through a vacuum – they
need a medium!
Notes:
1. Sound wave is independent on the motion of sound source
(such as car siren) but depends on the propagation of waves.
2. For the waves propagating through a rope, its velocity
depends on the rope characteristics (tension and rope
elasticity).
3. Sound waves travel as compression waves.

7.  What are the types of waves?
- When the wave particles vibrate back and forth along the
path that the wave travels. It is known as longitudinal
waves.
-When the wave particles vibrate in an up-and-down
motion. It is called transverse waves.

8. Decibels
 The decibel (dB) is the unit utilized to measure sound
intensity or loudness.
 Loudness corresponds to the amplitude of a wave and
can be measured by instruments such as an oscilloscope.
 Sounds greater than 120 dB can cause pain in human
ears.
 Sounds with an amplitude between 0 and 120 dB are
called audible. While, anything below 0 dB is considered
sub-audible.
 Humans can hear frequencies in range between 20 Hz
and 20 kHz.
 It is known that frequencies above 20 kHz are called
ultrasonic. While, frequencies below 20 Hz are called
infrasonic

9. Decibels (Cont.)
Source of Sound Level (dB)
Normal Breathing 10
Close Whisper 20
Library 40
Normal Speech 60
Busy Street Traffic 70
Subway Train 100
Loud Rock Music 115
Threshold of Pain 120
Jet Engine 140

10.  It occurred when, more than one wave can exist in the
same place at the same time and it is found that resulting
wave may be increased, decreased, or cancelled.
 Types of interference
1. Constructive Interference: Crest of one wave
overlaps the crest of another results in increased
amplitude as shown in the figure.
Interference

11. 2. Destructive Interference: Crest of one wave overlaps
the trough of another results in cancellation of amplitude
as shown in the figure.
Interference (Cont.)

12. - A receiver may hear two sound waves at the same
time:
 In phase: Compressions and rarefactions overlap
each other
 Out of phase: Compressions and rarefactions of
each wave are offset.
 If the crest of one wave overlaps the trough of
another, they will cancel.
Interference (Cont.)

13. Interference and Beats
(Cont.)

14. Standing Waves
 Created when a wave reflects on itself.
 Nodes: Parts of a standing wave which remain stationary.
 Antinodes: Positions on a standing wave with the largest
amplitudes.
Node
Antinodes

15. Standing Waves (Cont.)
Harmonics
To determine the harmonic of a standing wave, count the
antinodes.

16.  Is the apparent change in the
frequency of a sound caused
by the motion of either the
listener or the source of
the sound.
 If the source is moving as
fast or faster than the speed
of sound, the sound waves
pile up into a shock wave
called a sonic boom. A
sonic boom sounds very
much like the pressure wave
from an explosion.
Doppler Effect

17. {To Be Continued}
Good Luck