An Aeolian harp (æolian harp or wind harp) is a musical instrument that is played by the wind. It is named after Aeolus, the ancient Greek god of the wind. The traditional Aeolian harp is essentially a wooden box including a sounding board, with strings stretched lengthwise across two bridges. It is placed in a slightly opened window where the wind can blow across the strings to produce sounds. The strings can be made of different materials (or thicknesses) and all be tuned to the same pitch, or identical strings can be tuned to different pitches. Besides being the only strung instrument played solely by the wind, the Aeolian harp is the only stringed instrument that plays solely harmonic frequencies.
The Aeolian harp - already known in the ancient world – was first described by Athanasius Kircher (1602–1680) in his book Phonurgia nova (1673). It became popular as a household instrument during the Romantic Era, and Aeolian harps are still hand-crafted today. Some are now made in the form of monumental metal sound sculptures located on the roof of a building or a windy hilltop.
The quality of sound depends on many factors, including the lengths, gauges, and types of strings, the character of the wind, and the material of the resonating body. Metal-framed instruments with no sound board produce a music very different from that produced by wind harps with wooden sound boxes and sound boards. There is no percussive aspect to the sound like that produced by a wind chime; rather crescendos and decrescendos of harmonic frequencies are played in rhythm to the winds. Their vibrant timbres produce an ethereal, almost mystical, music that many people find alludes to higher realms.
The harp is driven by the von Kármán vortex street effect. The motion of the wind across a string causes periodic vortices downstream, and this alternating vortex causes the string to vibrate. Lord Rayleigh first solved the mystery of the aeolian harp in a paper published in the Philosophy Magazine. The effect can sometimes be observed in overhead utility lines, fast enough to be heard or slow enough to be seen. A stiff rod will perform; a non-telescoping automobile radio antenna can be a dramatic exhibitor. And of course the effect can happen in other media; in the anchor line of a ship in a river, for example.
Aeolian harps in literature and music
Aeolian harps are featured in at least two Romantic-era poems, "The Eolian Harp" and "Dejection, an Ode", both by Samuel Taylor Coleridge. In William Heinesen's novel The Lost Musicians set in Tórshavn, Kornelius Isaksen takes his three sons to a little church where, in the tower, they sit listening to the 'capriciously varying sounds of an Aeolian harp', which leads the boys into a lifelong passion for music. A lyre is mentioned in Percy Bysshe Shelley's "Ode to the West Wind" which is another name for an Aeolian Harp. The Aeolian harp is also mentioned in Shelley poem "Mutability."
El arpa eólica (The Aeolian Harp) is an alternate history novelette written by Óscar Esquivias. It was originally published in 2011 by Fábulas de Albión. The novelette depicts the life of Berlioz as a young student in Paris.
Henry Cowell's Aeolian Harp (1923) was one of the first piano pieces to feature extended techniques on the piano that included plucking and sweeping the pianist's hands directly across the strings of the piano. The Etude in A flat major Op. 25 No. 1 for piano (1836) by Frédéric Chopin is sometimes called the "Aeolian Harp" etude, a nickname given it by Robert Schumann. The piece features a delicate, tender, and flowing melody in the fifth finger of the pianist's right hand, over a background of rapid pedaled arpeggios. One of Sergei Lyapunov's 12 études d'exécution transcendante, Op. 11 No. 9, is named by the author "Harpes éoliennes" (aeolian harps). In this virtuoso piece, written between 1897 and 1905, the tremolo accompaniment seems to imitate the sounding of the instrument. In classical harp repertoire, an example of such imitation (mostly employing glissandi and arpeggios) is “La harpe éolienne”  by Félix Godefroid.
In 1972, Chuck Hancock and Harry Bee recorded a giant 30-foot-tall (9.1 m) Aeolian harp designed and built by 22-year-old Thomas Ward McCain on a hilltop in Chelsea, Vermont. United released their double LP titled The Wind Harp - Song From The Hill. (An excerpt of this recording appears in the movie The Exorcist.) In the spirit of this, in 2003 an Aeolian harp was constructed at the Burning Man festival. Australian artist, composer and sound sculptor Alan Lamb has created and recorded several very large scale aeolian harps.
Builders of pipe organs have included stops intended to imitate the sound and timbre of the aeolian harp. German builders were the first to include such a stop from the 1820s. The Aeolian Harp stop is not a harp—it is simply a rank of pipes using a low wind pressure and voiced to imitate the sound of the real instrument. It is, therefore, classified as a "string" stop. These stops are amongst the softest found on pipe organs.
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