A Brief History Of Noisy Tubes
Submitted by colink on 06/30/2008 05:21 PM
- Category: Philosophy
- Words: 1100
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A Brief History Of Noisy Tubes
A history of noisy tubes
From mans earliest times, it seems, he has always wanted to make a "noise" be it by banging things together or blowing down hollow tubes, of various materials. Naturally occurring things like animal horns and hollow tree branches were used initially and later manufactured pipes were introduced. What is happening in the pipe to create this "noise"? It all has to do with vibration. In a simple instrument like panpipes, which are hollow tubes of various lengths each of which give a single note. When the player blows across the top of the tube the air in the pipe starts to vibrate. At a certain frequency the tube is said to resonate and a sound is heard. The frequency or pitch of this note is dependent on the length of the pipe. A note can only be heard when the pipe resonates. Another demonstration of the phenomenon can be seen, or heard, by blowing across the top of a narrow necked bottle the pitch of the sound will vary dependent on the level of the liquid in the bottle. When a tube is resonating there is a "standing sound wave" developed in the tube with the maximum amplitude at the end of the pipe. This joint between the air in the pipe and the surrounding air is called the "reflection point". The vibration of the player's lips causes the vibration of the air in a brass instrument. The lips must match the frequency of the desired note as closely as possible. So how can we get more than one note out of a tube? To try to explain the physics of this in simple terms we turn to a man called August Kundt (1839-94) who developed an apparatus to measure the speed of sound in various fluids. The apparatus consists of a glass tube closed at one end into which a dry powder has been sprinkled. If a source of sound is placed at the open end of the tube, for example a small loudspeaker attached to an oscillator, sound waves generated by the loudspeaker enter the tube. If the frequency of the oscillator is varied until...
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