Sound

Sound is what can be professed by a living organism through its sense of hearing. Physically, sound is vibrational reflex energy that propagates through matter as a wave.

For humans, hearing is limited to frequencies between about 20 Hz and 20000 Hz, with the upper limit generally decreasing with age. Other species may have a different range of hearing. As a signal perceived by one of the major senses, sound is used by many species for detecting danger, navigation, predation, and statement. In Earth's atmosphere, water, and soil practically 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 worldly mammals, have also developed special organs to produce sound. In some species these became highly evolved to fabricate song and (in humans) speech. Furthermore, humans have developed culture and technology (such as music, telephony and radio) that allows them to generate, record, transmit, and broadcast sounds.

The mechanical vibrations that can be interpreted as sound can travel during all forms of matter: gases, liquids, solids, and plasmas. However, sound cannot circulate through space. The matter that supports the sound is called the medium. Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called density waves. Through solids, however, it can be transmitted as both longitudinal and oblique waves. Sound is further characterized by the generic properties of waves, which are frequency, wavelength, period, amplitude, intensity, speed, and direction (sometimes speed and direction are combined as a velocity vector, or wavelength and direction are combined as a wave vector). Transverse waves, also known as shear waves, have an additional property of divergence. Sound characteristics can depend on the type of sound waves (longitudinal versus transverse) as well as on the physical properties of the transmission medium.