`stĭks) [Gr.,=the facts about hearing], the science of sound sound, any disturbance that travels through an elastic medium such as air, ground, or water to be heard by the human ear. When a body vibrates, or moves back and forth (see vibration ), the oscillation causes a periodic disturbance of the surrounding air or other..... Click the link for more information. , including its production, propagation, and effects. Various branches of acoustics that deal with different aspects of sound and hearing include bioacoustics, physical acoustics, ultrasonics ultrasonics, study and application of the energy of sound waves vibrating at frequencies greater than 20,000 cycles per second, i.e., beyond the range of human hearing.
..... Click the link for more information. , and architectural acoustics. Unlike electromagnetic radiation electromagnetic radiation, energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if the motion is changing (accelerated), then the magnetic field varies and in turn produces an
..... Click the link for more information. , which can travel in the vacuum of free space, sound Waves Waves (Women Appointed for Voluntary Emergency Service), U.S. navy organization, created (1942) in World War II to release male naval personnel for sea duty. The organization was commanded until 1946 by Mildred Helen McAfee.
..... Click the link for more information. require a medium (solid, liquid, or gas) in which to travel. Another important difference is that sound travels much slower than electromagnetic radiation; the speed of sound in air at sea level is approximately 1000 ft/sec (300 m/sec), which is roughly a millionth the speed of light in air. Sound waves are longitudinal, which means that the material particles transmitting the waves oscillate in the direction of propagation. Important factors to be considered in working with sound include reverberation and interference interferometer. When the wavelength of the light is known, the interferometer indicates the thickness of the film by the interference patterns it forms. The reverse process, i.e., the measurement of the length of an unknown light wave, can also be carried out by the interferometer.
..... Click the link for more information. . Reverberation is the persistence of sound in an enclosed space caused by repeated reflections. Reflection of sound sometimes causes an echo echo, reflection of a sound wave back to its source in sufficient strength and with a sufficient time lag to be separately distinguished. If a sound wave returns within 1-10 sec, the human ear is incapable of distinguishing it from the orginal one.
..... Click the link for more information. . Depending on the location of the listener and the frequency of the sound, varying degrees of interference between the primary sound and its reflections will be produced. Reflection can be reduced by the use of sound-absorbent materials, which are usually soft and porous, such as draperies, upholstery, carpets, acoustic tile, or plaster. In a room, reflection is decreased by the presence of people and open windows and doors.
Bibliography
See J. Backus, The Acoustical Foundations of Music (1969); R. B. Lindsay, Acoustics (1973); A. D. Pierce, Acoustics (1981, repr. 1989).
acoustics
Science of production, control, transmission, reception, and effects of sound. Its principal branches are architectural, environmental, musical, and engineering acoustics, and ultrasonics. Environmental acoustics focuses on controlling noise produced by aircraft engines, factories, construction machinery, and general traffic. Musical acoustics deals with the design and use of musical instruments and how musical sounds affect listeners. Engineering acoustics concerns sound recording and reproduction systems. Ultrasonics deals with ultrasonic waves, which have frequencies above the audible range, and their applications in industry and medicine.
acoustics
acoustics [ə′küs·tiks]
Acoustics
The science of sound, which in its most general form endeavors to describe and interpret the phenomena associated with motional disturbances from equilibrium of elastic media. An elastic medium is one such that if any part of it is displaced from its original position with respect to the rest, as for example by an impact, it will return to its original state when the disturbing influence is removed. Acoustics was originally limited to the human experience produced by the stimulation of the human ear by sound incident from the surrounding air. Modern acoustics, however, deals with all sorts of sounds which have no relation to the human ear, for example, seismological disturbances and ultrasonics.
Basic acoustics may be divided into three branches, namely, production, transmission, and detection of sound. Any change of stress or pressure producing a local change in density or a local displacement from equilibrium in an elastic medium can serve as a source of sound. Transmission of sound takes place through an elastic medium by means of wave motion. The most important sound waves are harmonic waves, defined as waves for which the propagated disturbance at any point in its path varies sinusoidally with time with a definite frequency or number of complete cycles per second (the unit being the hertz). Acoustics deals with waves of all frequencies, but not all frequencies are audible by human beings, for whom the average range of audibility extends from 20 to 20,000 Hz. Sound below 20 Hz is referred to as infrasonic, and that above 20,000 Hz is called ultrasonic.
The detection of sound is made possible by the incidence of transmitted sound energy on an appropriate acoustic transducer, such as the ear. For modern applied acoustics, transducers such as the microphone, based on the piezoelectric effect, are widely used. Generally speaking, any transducer used as a source of sound is also available as a detector, though the sensitivity varies considerably with the type.
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