Acoustics - Vibrations Of A String, Vibrations Of An Air Column, Sound Production In General, Transmission Of Sound - Production of sound
body material medium human
Acoustics is the science that deals with the production, transmission, and reception of sound. Sound may be produced when a material body vibrates; it is transmitted only when there is some material body, called the medium, that can carry the vibrations away from the producing body; it is received when a third material body, attached to some indicating device, is set into vibratory motion by that intervening medium. However, the only vibrations that are considered sound (or sonic vibrations) are those in which the medium vibrates in the same direction as the sound travels, and for which the vibrations are very small. When the rate of vibration is below the range of human hearing, the sound is termed infrasonic; when it is above that range, it is called ultrasonic. The term supersonic refers to bodies moving at speeds greater than the speed of sound, and is not normally involved in the study of acoustics.
There are many examples of vibrating bodies producing sounds. Some are as simple as a string in a violin or piano, or a column of air in an organ pipe or in a clarinet; some are as complex as the vocal chords of a human. Sound may also be caused by a large disturbance which causes parts of a body to vibrate, such as sounds caused by a falling tree.
Additional Topics
To understand some of the fundamentals of sound production and propagation it is instructive to first consider the small vibrations of a stretched string held at both ends under tension. While these vibrations are not an example of sound, they do illustrate many of the properties of importance in acoustics as well as in the production of sound. The string may vibrate in a variety of different ways…
When air is blown across the entrance to an organ pipe, it causes the air in the pipe to vibrate, so that there are alternate small increases and decreases of the density of the air (condensations and rarefactions). These alternate in space, with the distance between successive condensations (or rarefactions) being the wavelength; they alternate in time, with the frequency of the vibration. One ma…
Thus, the production of sound depends upon the vibration of a material body, with the vibration being transmitted to the medium that carries the sound away from the sound producer. The vibrating violin string, for example, causes the body of the violin to vibrate; the "back-and-forth" motion of the parts of the body of the violin causes the air in contact with it to vibrate. That is,…
In order for sound to travel between the source and the receiver there must be some material between them that can vibrate in the direction of travel (called the propagation direction). (The fact that sound can only be transmitted by a material medium means that an explosion outside a spaceship would not be heard by its occupants!) The motion of the sound-producing body causes density variations i…
Physiological acoustics is the study of the transmission of sound and how it is heard by the human ear. Sound travels in waves, vibrations that cause compression and rarefaction of molecules in the air. The organ of hearing, the ear, has three basic parts that collect and transmit these vibrations: the outer, middle and inner ear. The outer ear is made of the pinna, the external part of the ear th…
The applications of acoustical devices are far too numerous to describe; one only has to look around our homes to see some of them: telephones, radios and television sets, compact disc players and tape recorders; even clocks that "speak" the time. Probably one of the most important from the human point of view is the hearing aid, a miniature microphone-amplifier-loudspeaker that is d…
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