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  3. The range in frequencies of musical sounds is approximately 20-20,000 cycles per second (cy/sec). Some people can hear higher fr

The range in frequencies of musical sounds is approximately 20-20,000 cycles per second (cy/sec). Some people can hear higher fr

admin2011-04-26  62
问题     The range in frequencies of musical sounds is approximately 20-20,000 cycles per second (cy/sec). Some people can hear higher frequencies khan others. Longitudinal waves whose frequencies are higher than those within the audible range are called ultrasonic frequencies. Ultrasonic frequencies are used in sonar for such purposes as submarine detection and depth finding. Ultrasonic frequencies are also being tried for sterilizing food since these frequencies kill some bacteria. Sound waves of all frequencies in the audible range travel at the same speed in the same medium. In the audible range, the higher the frequency of the sound the higher is the pitch. The term supersonic refers to speed greater than sound. An airplane traveling at supersonic speed is moving at a speed greater than the speed of sound in air at that temperature. Mach 1 means a speed equal to that of sound. Mach 2 means a speed equal to twice that of sound, etc.
    Musical sounds have three basic characteristics: pitch, loudness, and quality or timbre. As was indicated above, pitch is determined largely by the frequency of the wave reaching the ear. The higher the frequency the higher is the pitch. Loudness depends on the amplitude of the wave reaching the ear. For a given frequency, the greater the amplitude of the wave the louder the sound. To discuss quality of sound we need to clarify the concept of overtones. Sounds are produced by vibrating objects. If these objects are given a gentle push, they usually vibrate at one definite frequency producing a pure tone. This is the way a tuning fork is usually used. When objects vibrate freely after a force is momentarily applied, they are said to produce their natural frequency. Some objects, like strings and air columns, can vibrate naturally at more than one frequency at a time. The lowest frequency which an object can produce when vibrating freely is known as the object’s fundamental frequency. Other frequencies that the object can produce are known as its overtones. The quality of a sound depends on the number and relative amplitude of the overtones present in the wave reaching the ear.
A soprano would probably have a frequency of ______.
选项 A、200 cy/see
B、5,000 cy/sec
C、10,000 cy/sec
D、20,000 cy/sec
答案C
解析 女高音的频率很可能是10 000周/秒。作者在第一段开头说，音乐的频率范围大约在20～20 000周/秒之间，女高音的频率不可能是200周/秒，不可能是500周/秒，也不可能是20 000周/秒，因此可猜测10 000周/秒。
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