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Named after the Greek god of wind, Aeolus, aeolian harps are designed to produce sounds as the wind flows across them. Traditional aeolian harps consisted of a few integral components, such as a wooden box, two bridges, and a set of strings that stretch over the bridges along the length of the harp. Aeolian harp strings can be made out of different materials in varying thicknesses to achieve desired pitches.
A popular Romantic Era household instrument, the aeolian harp can still be found in modern homes across the globe. While many aeolian harps are handcrafted by skilled artisans, others are mass-produced by industrial machines. They are available in a range of sizes and can be constructed out of materials including steel and aluminum. Nearly any species of wood can be used in the construction of one of these harps.
Smaller versions of these harps are usually placed in open windows where gusts of wind can blow over their strings, producing sounds. Large aeolian harps can be constructed out of hard steel or a durable wood species such as oak and permanently placed atop a building or windy hilltop. Many monuments and public art displays are centered around large aeolian harps.
Aeolian harps operate by harnessing an effect known as a "vortex street," a phenomenon that results in the creation of spiral eddies of fluid or air known as von Karman vortices. Von Karman vortices, which travel in linear chains, are relatively common occurrences in the oceans and the atmosphere. The vortex motion that activates an aeolian harp is the same motion that causes a flag to ripple left and right in the presence of wind. Wind streaming across an aeolian harp's strings causes the strings to vibrate, creating sound.
Aeolian harps can be constructed to produce a wide range of sounds from low, almost inaudible hums to very loud tones. The strength of a wind gust can greatly affect the tone of an aeolian harp. No matter how heavy the wind, though, an aeolian harp's strings will only produce the tones or frequencies at which each string naturally resonates; the wind can only augment a string's natural tone.
In general, lightweight, tight, shorter aeolian harp strings offer higher tones, while heavy, loose, longer strings produce lower tones. Aeolian harp strings with smaller diameters also tend to make higher tones and strings with larger diameters make lower tones. The right string combination can produce a particular chord in the right wind conditions.