Information Booklet
Information Booklet

Sound Waves

Sound waves propagate in a variety of media, unaffected by the limits of human hearing, and range from tiny microacoustic waves in a plasma, to large-scale galactic waves in the interstellar medium. The presence of various sound waves in the surrounding media produces a continuum of interactive sound events which occur throughout the universe at various orders of magnitude and scale.

Sound waves occur in gas, liquids, organic and inorganic solids, in plasmas and superconductors, and in interplanetary, interstellar, and intergalactic media. Various sound waves are propagated in the Earth¹s atmosphere, hydrosphere, biosphere, and lithosphere, as well as on or near other planetary bodies and satellites, in the stellar wind, on the surface of stars, in interstellar dust clouds, in spiral galaxies, and in intergalactic clouds which occur in the regions between galaxies and clusters of galaxies.

Sound waves in the surrounding media oscillate at frequencies which range from billions of cycles per second, to a single cycle within a period of several days, months, or years. Sound waves propagate at speeds ranging from subsonic velocities of several feet per second, to hypersonic velocities which approach the speed of light.

The detectable range of sound extends from microacoustic waves produced by fluctuations of particles trapped within a sound field, to macroacoustic wave disturbances including weather patterns, ocean waves, seismic waves, global waves, solar waves, and galactic waves.

Sound Sources

Sound waves are generated by a variety of sound sources in which oscillations produced at the source are transmitted outward into the surrounding medium.

The physical dimensions, material substance, density, and elasticity of a sound source, and the actions and forces which cause the source to vibrate, determine the vibrational properties of the corresponding sound wave.

Normally an acoustic sound source vibrates at a frequency which is related to the length or diameter of the source, and depends upon its various dimensions, mass, density, and tension. The intensity of the action or force which causes a sound source to vibrate determines the amplitude of the corresponding sound wave.

Acoustic wave disturbances in the surrounding media are caused by stationary or moving sound sources which vibrate freely or by a forced agitation, by the angular rotation of solid bodies which are large compared to the particles in the medium in which they are contained, by the translation of objects or steady flow of wind or other substance through a medium, by compressional or magnetic lines of tension or stress, by interactions which occur at the boundary interface between different media or between different regions of the same medium, or by electromagnetic or electromechanical oscillation.

Wave Forms

Various generic wave forms are graphically represented by the symbols in the Acoustic Wave Spectrum. These waves propagate in a variety of media at different speeds, and have different vibrational characteristics depending on their source. They include traveling waves, standing waves, internal waves, surface waves, trapped waves, thermal waves, shock waves, and plasma waves.

Every sound wave propagates as a traveling wave or a standing wave. In addition sound waves may propagate in other forms sush as on the surface of a medium, as a shock wave, etc. Symbols for traveling and standing waves are graphically displayed to the left of each wave form on the chart. Symbols for the other wave forms are displayed to the right.

Traveling Wave

A traveling wave is a progressive wave which propagates in a linear direction within a medium, or within a confined region of a medium. A normal sound produced in air forms a typical traveling wave.

Standing Wave

A standing wave is a nonlinear traveling wave which is produced within a confined medium or region of a medium.

Standing waves travel in a cyclical path within the region of a medium in which the wave is confined. Standing waves propagate by continuous or partial reflection, by dispersion, as radial waves which travel a short distance from the source, or as periodic formations which evolve over time. Internal Wave

An internal wave is a sound disturbance caused by spontaneous fluctuations within a medium. Internal waves are normally produced by interaction at the boundaries between the various layers of a medium, or by turbulence or heat sources. Internal waves propagate as global and local thermal cycles in crystalline solids, including seismic waves caused by earthquakes and underground nuclear explosions.

Internal waves are also spontaneously generated in organic substances such as bone tissue and trees, in plasmas, and in electrically conductive solids, including various metals, semiconductors, and superconductors.

Surface Wave

A surface wave propagates on the free surface of a liquid or solid. In liquids, surface waves describe a forward rolling motion, such as ocean waves, in which crests and troughs are generated in the free space just above the surface. Surface waves in liquids also propagate as ring-shaped waves which travel outward as an expanding series of concentric circles.

In solids, waves are dispersed on the surface of a sound source forming standing waves which travel in a nonlinear path along the surface boundary, or along tensional nodes associated with various areas of the surface. In addition there are small-scale stress waves which travel along the surface of crystalline solids, sand and snow waves, and seismic waves which propagate along the surface of a planetary body.

Trapped Wave

A trapped wave is a deflected wave which is continuously reflected or trapped within an enclosed boundary. Trapped waves occur between layers of the atmosphere of the Earth or other planets, within the Earth's liquid core, as microthermal waves trapped within normal sound waves in air, liquids, and organic substances, and within the interior of the Sun or other hot stars.

Thermal Wave

A thermal wave is a sound disturbance caused by periodic fluctuations in the temperature or velocity of the particles in a confined medium, as opposed to normal sound waves which are distinguished by pressure disturbances.

Microthermal waves are infinitesimal fluctuations in the velocity of the trapped particles which accompany normal sound waves in air, electron waves in a plasma, small-scale stress waves in a superconductive solids, and so-called second sound waves in supercooled liquid helium. Macrothermal waves are large-scale fluctuations of the atmo-sphere or hydrosphere of the Earth or other planetary bodies.

Shock Wave

A shock wave is caused by a violent disturbance of the particles in a medium.

When a vibrating force causes a sound disturbance of sufficient strength that the amplitude of the disturbance is nearly unrestricted, the rapid acceleration caused by the strength of the initial disturbance piles up a density of particles in front of the wave which rapidly steepens, producing a sudden discontinuity in the path of travel. The discontinuity in a shock wave creates an irregular vibration of the wave which travels outward in all directions at supersonic speed without further disruption.

Shocked sound waves are produced by small disturbances such as the bursting of a balloon or a small explosion, or by large disturbances such as a flash of lightning causing a thunderous sound, the motion of a foreign object such as an airship or meteorite traveling at supersonic speed, or by various chemical or nuclear explosions.

In addition, large-scale radial waves, or so-called standing shock waves, are produced by the rotation of stars or galaxies, and by stellar explosions including supernovas.

Plasma Wave

A plasma wave is produced by a local disturbance caused by instabilities of the motions in a plasma medium.

A plasma is a medium of gaseous matter which differs from other gas by its high temperatures, electrical and thermal conductivity, by complex particle and wave interactions, and by the emission of electromagnetic radiation.

Plasma media include stars, the solar and galactic wind, the upper atmospheres of various planetary bodies, flames, chemical and nuclear explosions, electrical discharges, and certain metals including copper, silver, and gold.

A plasma medium may contain electromagnetic waves, as well as sound waves of various kinds.

When sound waves and electromagnetic waves interact in a plasma medium, they produce normal, electroacoustic, and magnetoacoustic waves which travel at or near the speed of sound, or at hypersonic speeds.