Nov 25, 2010


Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.

Perception of sound
For humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz)[2], although these limits are not definite. The upper limit generally decreases with age. Other species have a different range of hearing. For example, dogs can perceive vibrations higher than 20 kHz. As a signal perceived by one of the major senses, sound is used by many species for detecting danger, navigation, predation, and communication. Earth's atmosphere, water, and virtually any physical phenomenon, such as fire, rain, wind, surf, or earthquake, produces (and is characterized by) its unique sounds. Many species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce sound. In some species, these produce song and speech. Furthermore, humans have developed culture and technology (such as music, telephone and radio) that allows them to generate, record, transmit, and broadcast sound.

Physical of sound
The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter: gases, liquids, solids, and plasmas. The matter that supports the sound is called the medium. Sound cannot travel through a vacuum.

Noise is a term often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal.

Effect of Noise on Man
All sounds that are distracting, annoying, or harmful to everyday activities such as work, rest, entertainment, study and so forth are regarded as noises. In fact, any sound judged by the recipient as undesirable can be considered as a noise.
Whether or not a sound is undesired by a person will depend on a number of factors, e.g.
(a) Loudness.
(b) Frequency.
(c) Continuity.
(d) Variation with time.
(e) Time of occurrence.
(f) Information content.
(g) Origin of the sound.
(h) Recipient's state of mind and temperament.
(i) Background noise level.

In general, the effects of noises are:
(a) Hearing Loss
Exposure to high noise levels causes hearing loss. This loss of hearing may be temporary, permanent, or a combination of both. Temporary hearing loss, also called Temporary Threshold Shift (TTS), results from exposure to short-term loud noises. As time passes, temporary hearing loss will disappear. However, if the human ear is not given the opportunity to recover, permanent hearing loss or Permanent Threshold Shift (PTS) will result because of the destruction of parts of the ear. Permanent hearing losses cannot be treated.