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1. Definition of Sound.- There are various definitions of sound. Therefore at the start it is well to have an understanding as to the definition of the word as used in this and in the succeeding chapters of this book.

Sound can be considered as a series of vibrations of the air of such frequency, or pitch, that it is audible to the human ear.

Sound is sometimes defined as an audio sensation in the ear. Such a definition requires a person to be located in the vibrating air before sound can exist, and is therefore inconvenient in a discussion of sound reproduction.


2. Production of Sound.- Sound is produced when air is set into vibration by any means whatsoever, provided that the frequency of vibration is such that it is audible, but sound is usually produced by some vibrating object which is in contact with the air. If we take a string, such as used on a banjo or similar instrument, stretch it taut between two fairly solid supports a few feet apart and pluck it, sound is produced which dies down in a fairly short time. When the string is plucked it springs back into position, but, due to its weight and speed, it goes be­yond its normal position, oscillates back and forth through its normal position, and gradually comes to rest. As the string moves forward it pushes air before it and com­presses it, also air rushes in to fill the space left behind the moving string. In this way the air is set into vibration. Since air is an elastic medium, the disturbed portion transmits its motion to the surrounding air so that the disturbance is propagated in all directions from the source of disturbance.

If the string is connected in some way to a diaphragm such as the stretched drum-head of a banjo, the motion is transmitted to the drum. The drum, having a large area exposed to the air, sets a greater volume of air in motion, and a much louder sound is produced.


Chapter One Pages
[1] [2] [3] [4] [5] [6] [7] [8] [9]

[1] [2] [3] [4] [5] [6] [7] [8] [9]
[10] [11] [12] [13] [14] [15]

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