1. By
Dr. S.V. Kshirsagar

2. SOUND is the result of changing air pressure over time
SOUND is the result of changing air pressure over time. A more technical definition:
Sound is mechanical energy in the form of pressure variances in an elastic medium. These pressure variances propagate as waves from a vibrating source.
Changes in air pressure (air being a propagating medium) can be represented by a WAVEFORM, which is a graphic representation of a sound. In reality, sound waves propagate through the air in LONGITITUDAL WAVES (and not TRANSVERSE WAVES):

3. Nature of Sound Waves
Sound is one kind of longitudinal wave, in which the particles oscillate to and fro in the same direction of wave propagation. Sound waves cannot be transmitted through vacuum. The transmission of sound requires at least a medium, which can be solid, liquid, or gas.
 condensation
rarefaction

4. Characteristics of Sound
A sound can be characterized by the following three quantities:
Pitch.
(ii) Quality.
(iii) Loudness.

5. Figure 2 shows the frequencies of same common sounds.
Pitch is the frequency of a sound as perceived (supposed) by human ear. A high frequency gives rise to a high pitch note and a low frequency produces a low pitch note.
Figure 2 shows the frequencies of same common sounds.

6. humming of mosquito
Buzzing bees

7. roaring of lion

8. A pure tone is the sound of only one frequency, such as that given by a tuning fork or electronic signal generator.
The fundamental note has the greatest amplitude and is heard predominantly because it has a larger intensity. The other frequencies such as 2fo, 3fo, 4fo, are called overtones or harmonics and they determine the quality of the sound.
Loudness is a physiological sensation. It depends mainly on sound pressure but also on the spectrum of the harmonics and the physical duration.

11. The Intensity of Sound The intensity of sound, at a given distance, depends upon the amplitude of the waves.
Thus, a tuning fork gives out more energy in the form of sound when struck hard than when struck gently. You should remember that when a tuning fork is struck, the sound is omnidirectional (heard in all directions), because the sound waves spread out in all directions. As the distance between the waves and the sound source increases, the energy in each wave spreads over a greater area; hence, the intensity of the sound decreases. Therefore, the sound is heard almost at its original intensity at the opposite end of the speaking tube. The unidirectional megaphone and the directional loudspeaker also prevent sound waves from spreading in all directions.

12. * With the proper combination of these characteristics, the tone is pleasant to the ear.
* With the wrong combination, the sound quality turns into noise.

15. When a sound wave travels outward in all directions and come across an obstacle such as a wall, floor or ceiling surface the direction of the sound will be changed or reflected, The direction of travel of the reflected sound will be at the same angle as the original sound striking the surface as shown in (FIGURE 10) The immediate effect of multiple reflections is an increase in the sound intensity caused by the reflections. A listener will hear the direct sound arriving at the ear along with all of the multiple reflections. Thus the combined loudness of the direct sound and the reflected sound will be greater than the direct sound alone.

16. Thanks