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Sound or Acoustics

Sound is a form of energy that we receive with the help of our ears and feel a specific type of sensation in our brain. It originates from a mechanically vibrated body; the vibration of the body causes disturbances in its surrounding medium. The disturbance when reaches our ears, the ear drum is also set into similar vibration and we have a sensation of sound with our auditory organs.

Reflection of sound and Echo

Sound waves reflect from a surface obeying the laws of reflection of light waves.

A tiny mirror reflects light waves but not sound waves, because, very small wavelengths of light reflect from the tiny mirror but the spread of mirror cannot accommodate longer wave lengths of sound and hence reflection of sound does not occur.

Echo

In a large open space or in a valley, when a loud sound is produced, the sound repeats several times which are perceived clearly after the initial sound. This repetition of a sound, distinguishable from the original sound is called Echo. It is occurred as a transient sound; the minimum distance of the reflector from the source of sound is half of 33.2 m i.e. 16.6 m. At higher temperature velocity of sound increases, so this distance for the reflector also increases.

The different feelings and sensations created in our brain on reception of sound may be divided in two classes - musical sound and noise. If a sound creates a pleasing sensation it is a musical sound. If a sound is annoying and causes displeasure, it is called noise. In science, a sound is considered musical if it is generated from a source that vibrates continuously and periodically. Examples of Musical sound: sounds of musical instruments, sitar, sarod, violin, etc.

Noise is the sound emitted by a source vibrating in irregular, aperiodic and discontinuous manners. Examples: Sounds of shouting, thunder claps, gunfire, etc.

Characteristics of musical sound are: (a) Intensity, (b) Pitch, (c) Quality or Timbre.

Tone and Note

Sound of one frequency is Tone. Note is a sound mixed of different frequencies.