1. BASIC THEORY OF SOUND
Sound is a vibration in an elastic medium such as air, water, building
materials and earth. Sound energy progresses in atmospheric pressure
and travel a great distance. Sound is the physical phenomenon that
encourages the sense of hearing. It is generated by vibrated bodies in the
form of waves of compression and rarefaction in the air. A full circuit by a
displaced particle is called a cycles. The time required for one complete
cycle is called period and the number of complete cycles per second is the
frequency of vibration.
Wavelength of Sound: It is the distance a sound wave traveling during one
cycle of vibration or wavelength is the distance between adjacent regions where
identical conditions of particle displacement occur.

3. To fine the wavelength of sound in air at a specific frequency by the following
equation;
λ=
Where λ = wavelength in Feet
F = frequency in Hz
1130 = speed of sound feet per second
Velocity of Sound: The speed at which the sound travels is called as velocity of
sound. Velocity of sound primarily depends on the elasticity and density of the
medium. In air, at normal temperature and atmospheric pressure the velocity of
sound is approximately 1130 feet per second. Sound may travel at 16,000 ft/s along
steel pipes and duct walls. Speed of sound in concrete is about 12,000 ft/s. Some of
the important points in sound velocity as follows;
 These sound waves can travel from source of origin by air in different directions
and these sound waves set the ear drum to vibrate then the vibrating ear drum
translates by the brain in to sound sensation of hearing.

4.  In humans, hearing takes place whenever vibrations of frequencies from 15 hertz
to about 20,000 hertz reach the inner ear. The hertz (Hz) is a unit of frequency
equaling one vibration or cycle per second. Sound has the following characters
 When the sound waves are periodic, regular and long continued, they produce
pleasing effect of sound and this sound is also called audible sound.
 When the sound waves are non-periodic, irregular and very short duration, it
produces displeasing effect of sound and this sound is also called audible noise.
 Sound waves are longitudinal waves and they can move backward and forward
along a line in the direction of in which sound is traveling.
 The velocity of sound depends upon nature and temperature of medium through
which it travels. The velocity of sound can be measured by meter per second.
See the velocity of sound through different medium given bellow.

5. Name of the medium Velocity of sound at 200C in m/s
Atmospheric air 343
Hydrogen 1305
Nitrogen 338
Pure water 1450
Brick 4300
Concrete 4000
Granite 6400
Glass 5000-6000
Aluminum 5100
Iron 4700-5100
Copper 3900
Brass 3500
Silver 2600
Cork 450-530
Rubber 40-150

6. Propagation of Sound: 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. 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.

7. Diffraction of Sound: The bending of sound waves due to obstacles called
as diffraction of sound. Sound diffraction causes decreasing of frequency,
loudness, pitch ate. Example if you brought a concert ticket without looking
seating arrangement chart. When you enter inside the concert hall your seat
will be behind a huge pillar. After starting the film you cannot hear a clear
voice due to the obstacle in between you and the music source and because
of this the sound wave can bent around the pillar before reaching you.
Hearing Sensitivity: The ability of understanding or listening of sound is called as
sensitivity of hearing. The hearing of sound depends up on person eardrum, intensity of
sound, type of sound tone, distance between the source and the listener, climatic
conditions. A healthy young person is capable of hearing sound form about 20Hz to
20,000 Hz. The extent of hearing sensitivity for an individual depends on many factors like
age, sex, ethnicity (character of person), previous exposure to high noise level etc.

8. Physical Character of Sound: The physical characters sound as follows;
Frequency
Loudness or intensity
Quality or timbre.
Frequency or Pitch: It is the number of cycle or pressure vibrations produced by a
body in unit of time. The greater the number of cycles or vibrations, the higher will be
the pitch. The grater the frequency higher the pitch and the lesser the frequency the
lower the pitch. Frequency of sound is the measure of the quality of sound. Frequency
of sound can be measured in cycles per second or hertz (Hz). A healthy young person
is capable for hearing sound energy from about 20 to 20000 Hz.

9. Loudness or Intensity: It is the flow of wave energy crossing per unit
time through unit area. Sound intensities are measured in decibels (dB).
For example, the intensity at the threshold of hearing is 0 dB, the
intensity of whispering is typically about 10 dB. Sound intensities are
arranged on a logarithmic scale due to a wide range of variations of the
intensity of sound. Intensity of sound can be calculated by the following
equation;
I=
Where I = sound intensity (w/m2
W = sound power (Watt)
d = distance form sound source (m)

10. Quality or timber: It is the quality of musical note. It is one of the important
characters of the sound that allows the ear to differentiate between tones produced
by different instruments when the sound waves are identical in aptitude and
frequency. Example if a person played a violin, second person played piano and
third person a tuning fork, all at the same volume, the tones are identical in
frequency and amplitude, but different in quality. From these three sources, the
simplest tone is produced by the tuning fork; the sound
Because of the acoustical properties of the ear and the resonance properties of the
ear's vibrating membrane, however, it is doubtful that a pure tone reaches the inner
hearing mechanism in an unmodified form. The principal component of the note
produced by the piano or violin also has a frequency of 440 Hz, but these notes
also contain components with frequencies that are exact multiples of 440, called
overtones, at 880, 1320, and 1760 Hz, for example. The exact intensity of these
other components, which are called harmonics, determines the quality, or timbre, of
the note.

11. Amplitude or Volume: Amplitude is the characteristic of sound waves that
humans perceive as volume. The amplitude corresponds to the distance that air
molecules move back and forth as a sound wave passes through them. As the
amount of motion in the molecules is increased, they strike the ear drum with
progressively greater force. This causes the ear to perceive a louder sound. This
comparison of samples at low, medium, and high amplitudes demonstrates the
change in sound caused by altering amplitude. These three waves have the same
frequency, and so should sound the same except for a perceptible volume
difference.
Measurement of sound: Generally sound can measure in terms of pressure level
or decibel (dB) and it is used as convent unit to measure the magnitude of sound.
By measuring the sound, we can achieve following objects;
Sound measurement can helps us to improving of building acoustics and loud speakers and thus
improve our enjoyment of music both in concert hall and home;
Sound measurement can indicates when sound may causes hearing damage and it helps in taking
corrective measures to be avoiding damage;

12.  It permits evaluation of the hearing sensitivity of individuals;
 It permits the improvement of quality of our daily lives.