A Catalog of Sounds (Week 3)

The loudest known sound, recorded in modern times, was the eruption in 1883 of the volcanic island of Krakatoa, located in the Dutch East Indies. The volcano erupted with such force that it could be heard in Australia, two thousand miles away. The explosions lasted for 36 hours, and blew off half the island. The final outburst had enough sound energy to circumnavigate the Earth 7 times before it eventually dissipated.

The softest sound which can be detected by the human ear occurs in the range of about 0 to 5 decibels, which is equivalent to the sound of air molecules moving inside the mouth of a drinking glass. By definition, the softest sound that can be detected by an acoustic sensor requires the minimum amount of energy which is necessary to produce a vibrating wave motion in a medium.

The highest sounds, known as hypersounds, are generated at frequencies which vibrate at billions of times per second. These microcycles include the oscillation of the tiniest known particles of matter.

The lowest sounds are produced by large objects, and are known as infrasounds. Infrasounds have very long wavelengths with a single vibration occurring within a period of millions of years. These include planetary, interplanetary, stellar, galactic, and intergalactic cycles. The very lowest sounds are generated in large intergalactic gas clouds caused by the galactic wind and stellar explosions.

Normal sounds propagate through the air at sea level at a speed of about 1100 feet per second, or 750 miles per hour. Sounds travel faster in liquids, faster still in solids, and fastest of all in hot gases known as plasmas. The fastest sounds propagate at supersonic speeds within a range of several thousand miles per second, to hypersonic speeds which approach the speed of light. The very fastest sounds are plasma waves which propagate in a low-density medium such as the upper atmosphere of a planet or the stellar wind, or high-density sounds which travel within the interior of stars, or are generated by chemical and nuclear reactions.

Slow sounds propagate at subsonic speeds, which range from several feet per second to several hundred feet per second. The slowest sounds form standing wave patterns in the place where they are generated. Standing waves do not travel through a medium like normal sound waves, but remain at or near their source, such as the wave patterns which are formed on the head of a drum. In a standing wave pattern, the frequency of the wave or waves is the same as its traveling speed. The frequency and the velocity of the wave are identical because the wave is traveling through space in a recurrent, orbital path. Global standing wave patterns include large-scale geological, ecological, biological, social and cultural cycles. The very slowest sounds include the spins, orbits, beats, and lifecycles of the largest astronomical bodies, such as galaxies, intergalactic gas clouds, galactic groups, clusters, and superclusters.

The shortest sounds are those which can generate enough energy from a sound source to form a wave pattern.

Sounds with the longest duration are known as solitons. Solitons form atypical waves such as a tidal bore, which may travel for miles down a narrow river or stream. Normally, sound waves spread-out then disperse very quickly as the distance from their source increases. However, when the dispersion of the wave is exactly balanced by the tendency of the wave to narrow, the sound will keep on going.

The most resonant sounds result from the perfectly regular rhythms of stars known as cepheid variables. Cepheid variables alternately expand and contract to as much as 30 percent of their normal size. These regular changes in size are accompanied by changes in brightness, temperature, and spectral type.

The most irregular rhythms belong to the complex sound waves which form so-called white noise. By definition, noise contains waves of different frequencies, any of which has no multiple or submultiple relationship to the others.

The most characteristic sounds are those which are uniquely expressive or familiar. Normally, an expressive musical pattern or phrase is underlined by psychological tensions which directly confront the emotions of the listener. The familiar childhood ridicule "Nah, Nah-Nah, Nah, Nah" or the most sublime melodies of Schubert or Mozart are extreme examples. Individual sounds with deep psychological associations will also create a strong impression, such as the sound of a crying baby, or the roar of a wild animal.

The least characteristic sounds are those which are void of emotional or intellectual tensions, or sounds that fail to engage our attention at all. These sounds may be physically soothing, such as the constant lapping of ocean waves on the beach, flat monotonic utterances of speech, or commercial ambient sounds.

The most intense sounds are shock waves. Shock waves travel at supersonic speeds and are produced by small disturbances such as the bursting of a balloon or small explosion, or by large disturbances such as a flash of lightning causing a thunderous sound, a foreign object such as an airship or meteorite traveling at supersonic speed, or by various chemical or nuclear explosions. The most intense sounds are standing shock waves, produced by the rotation of stars or galaxies, and by stellar explosions including supernovas.

The most reposed sounds are those which are least energetic. These may include slight ripples on a pond produced by a gentle breeze, the infinitesimal movement of molecules on a still day, or the slightest interaction of particles in a magnetic field.

The simplest sound is a pure tone, or so-called sine wave. Most sounds consist of many sound waves containing different vibrations, while a pure tone contains only a single vibration.

The greatest density of sound on Earth may occur in the tropical rain forest, where millions of sound-producing creatures are packed into a single listening environment. Although, rush-hour in any major city of the world will produce an impenetrable cacophony of sound.

Microacoustic waves are the smallest known sound waves. The smallest sounds on Earth are generated spontaneously by heat fluctuations of the trapped particles within a normal sound wave. In addition, microacoustic waves are generated by spontaneous vibrations within the bone structure of the middle ear, and in plasmas and superconductors.

The largest sounds are macroacoustic waves which are large-scale oscillations that are generated within, on, or near planetary bodies, stars, and galaxies, including large-scale disturbances of a planetary atmosphere, hydrosphere, or lithosphere. These oscillations include global weather patterns, ocean waves, and seismic waves, as well as solar waves, large-scale fluctuations of the solar wind and interstellar dust clouds, and galactic waves.

Imagine the very first sound on Earth. The first sounds used for the purpose of communication on Earth were probably made by insects.

Imagine the last sounds on Earth. Imagine the sounds of a collapsing solar system. Imagine the final sounds of an exploding or imploding universe.

J. H.