1. Sound is defined physically as fluctuations in pressure in an elastic medium like air, while subjectively it is the auditory sensation these fluctuations produce. 2. Sound waves are created by outwardly traveling layers of compression and rarefaction of air particles, causing pressure fluctuations without changing the particles' positions. 3. A sound wave's amplitude is the distance a particle moves from its rest position during one full displacement cycle, while its frequency is the number of cycles per second. The speed of sound is about 1130 feet per second at room temperature.

1. Aoustics
Pankaj Kumar

2. Origin and propagation of sound. Speed of sound
The word "SOUND” has two definitions:
 Physically speaking it is a fluctuation in pressure, a particle
displacement in an elastic medium, like air; this is objective sound;
 Physiologically it is an auditory sensation evoked by the fluctuation
described before; this is subjective sound.
Sound wave motion is created by outwardly traveling layers of
compression and rarefaction of the air particles, i.e. by pressure
fluctuations.
The air particles that transmit sound waves do not change their normal
positions.
They vibrate about their equilibrium positions only.

3. Sound Waves:
amplitude & frequency (cycles)

4. A single, full displacement "activity" of the particle is called a Cycle. The
distance the particle moves from its rest position is called Amplitude.
The speed of the sound wave motion at68°F (200°C)room temperature is
about 1130 ft per sec (344 m per sec).
Frequency, Pitch, Wavelength
 The number of displacements (vibrations) that the particles undergo in
one second is called Frequency, usually stated in cycles per second
(abbreviated cps or r/s)
 e.g., if a string undergoes 261 oscillations in one second(261 cps),it will
produce in the eardrum of an observer the subjective tone of middle
"C".
 Frequency is an objective physical phenomenon which can be measured
by instruments.
Frequency

5.  The attribute of an auditory sensation which enables us to order sounds
on a scale extending from low to high is called Pitch.
 It is the subjective physiological equivalent of frequency. The pitch
depends primarily ,upon the frequency of the sound stimulus.
 A sound sensation having pitch is called Tone. Pure tone (or simple tone)
is a sound sensation of a single frequency characterized by its singleness
of pitch. It can be produced by striking a tuning fork.
Pitch
Wavelength