Wind Harp Physics
When you pluck the string of a regular harp, the string sounds its fundamental
note. But when the wind blows across the string and you hear it, the note is
much higher - it is a harmonic of the fundamental note.
The ancient Greek mathematician Pythagorus is credited with the first historical
description of harmonics. He discovered that if a string was shortened to exactly
half of its original size, the resulting tone would be an octave above the
original note. If he took only half of the second string's length, the result
would be another octave higher. Other divisions of a string will result in
other interval relationships, like fifths and thirds. These related notes
above the fundamental note are harmonic overtones.
When a string is plucked, we hear mainly the fundamental note, but in addition,
the harmonic overtones are also present.
When the wind plays a string, it does not play the fundamental tone, but only
the series of overtones. That is why the sounds are so high-pitched and fairy-like.
On the giant wind harps, the sounds are lower and sound more mysterious than
fairy-like because the strings are so long, but the tones are still harmonics
of the fundamental pitch of the string.
Air and water are both considered fluids, and behave very similarly. (Of course,
it's a lot easier to see the effects in water.) Wind does not always blow
constantly or steadily. And when it bumps into objects, curls and eddies
are created, just like water in a stream when it runs over or against rocks.
When the wind blows past a string, little spirals of air move to either side
(the wind stream "sheds vortices"). These spirals or vortices form alternately and
create an oscillation. The number of oscillations in a given time (a second
is the amount of time generally used) is called the frequency.
When the wind is consistent over a long enough time and the vortex shedding
occurs in a regularly repeating pattern, the string will sound IF the
frequency of the oscillation matches the frequency of the string tuning.
This depends on the speed of the wind.
Aeolian Harps and Wind Harps
An Aeolian harp is usually constructed as a rectangular sound box (the size
of the box is determined by the width of the window in which it will be placed)
with several strings of equal length, tuned to the same note. This means
that only one wind speed will create vortices which match the frequency
of the strings. The chances of the wind having exactly the right speed and
coming from exactly the right direction to reach the window means that
the Aeolian harp may not play very often.
However, Ron's wind harps are built like regular harps, with strings of
varying lengths and notes, and the wind harps are placed outdoors in
unobstructed places, so there is a wider range of wind directions, wind
speeds and vortice frequencies that can cause strings to sound, and the
chances are greater that these harps will play.
Wind Harp Main Page
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Wind Harp Wish List
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Wind Harp Physics
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Copyright © 1984, 2001 by Ron Konzak
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