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. Sound also travels through plasma.
Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. During propagation, waves can be reflected, refracted, or attenuated by the medium.
Sounds is a mechanical wave that is an oscillation of pressure transmitted through some medium (like air or water), composed of frequencies within the range of hearing.
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, Sounds, ultraSounds and infraSounds. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustical engineering may be called an acoustic or audio engineer. The application of acoustics can be seen in almost all aspects of modern society, subdisciplines include: Aeroacoustics, Audio signal processing, Architectural acoustics, Bioacoustics, Electroacoustics, Environmental noise, Musical acoustics, Noise control, Psychoacoustics, Speech, UltraSounds, Underwater acoustics and vibration.
Propagation of Sounds
Sounds is a sequence of waves of pressure that propagates through compressible media such as air or water. (Sounds can propagate through solids as well, but there are additional modes of propagation). Sounds that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of Sounds waves range from 17 m to 17 mm. During propagation, waves can be reflected, refracted, or attenuated by the medium.
The behavior of Sounds propagation is generally affected by three things:
A relationship between density and pressure. This relationship, affected by temperature, determines the speed of Sounds within the medium.
The propagation is also affected by the motion of the medium itself. For example, Sounds moving through wind. Independent of the motion of Sounds through the medium, if the medium is moving, the Sounds is further transported.
The viscosity of the medium also affects the motion of Sounds waves. It determines the rate at which Sounds is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.
When Sounds is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).
Spherical compression waves
The mechanical vibrations that can be interpreted as Sounds are able to travel through all forms of matter: gases, liquids, solids, and plasmas. The matter that supports the Sounds is called the medium. Sounds cannot travel through a vacuum.
Longitudinal and transverse waves
Sounds is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. Through solids, however, it can be transmitted as both longitudinal waves and transverse waves. Longitudinal Sounds waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation.
Matter in the medium is periodically displaced by a Sounds wave, and thus oscillates. The energy carried by the Sounds wave converts back and forth between the potential energy of the extra compression (in case of longitudinal waves) or lateral displacement strain (in case of transverse waves) of the matter and the kinetic energy of the oscillations of the medium.
Sounds wave properties and characteristics
Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal axis represents time.
Sounds waves are often simplified to a description in terms of sinusoidal plane waves, which are characterized by these generic properties:
Frequency, or its inverse, the period
Speed of Sounds
Sometimes speed and direction are combined as a velocity vector; wavenumber and direction are combined as a wave vector.
Transverse waves, also known as shear waves, have the additional property, polarization, and are not a characteristic of Sounds waves.
Speed of Sounds
U.S. Navy F/A-18 approaching the Sounds barrier. The white halo is formed by condensed water droplets thought to result from a drop in air pressure around the aircraft (see Prandtl-Glauert Singularity).
Main article: Speed of Sounds
The speed of Sounds depends on the medium the waves pass through, and is a fundamental property of the material. In general, the speed of Sounds is proportional to the square root of the ratio of the elastic modulus (stiffness) of the medium to its density. Those physical properties and the speed of Sounds change with ambient conditions. For example, the speed of Sounds in gases depends on temperature. In 20 °C (68 °F) air at sea level, the speed of Sounds is approximately 343 m/s (1,230 km/h; 767 mph) using the formula “v = (331 + 0.6 T) m/s”. In fresh water, also at 20 °C, the speed of Sounds is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of Sounds is about 5,960 m/s (21,460 km/h; 13,330 mph). The speed of Sounds is also slightly sensitive (a second-order anharmonic effect) to the Sounds amplitude, which means that there are nonlinear propagation effects, such as the production of harmonics and mixed tones not present in the original Sounds (see parametric array).
Perception of Sounds:
The perception of Sounds in any organism is limited to a certain range of frequencies. For humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz), 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, but are deaf to anything below 40 Hz. As a signal perceived by one of the major senses, Sounds 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 Soundss. Many species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce Sounds. 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 Sounds. The scientific study of human Sounds perception is known as psychoacoustics.