Webster in a rare moment of poetry describes the Aeolian Harp as "a
box-shaped musical instrument having stretched strings usually tuned
in unison on which the wind produces varying harmonics over the same
fundamental tone." Ah ha! Telephone poles don't count unless you tune
the wires and add a resonant sound box. The following information,
largely purloined from the New Grove Encyclopedia of Musical
Instruments isn't particularly informative, but probably is sufficient
to try to build an Aeolian harp.
Considerable scientific investigation has been done on the Aeolian
harp and yet the mechanism through which tones are generated is not
completely understood. (In fact, I would suggest, hardly understood
at all.) In 1650 Kircher noticed that several notes were heard from
one string and suggested that the string acted to the wind as a prism
does to light, breaking the whole into its components. His
contemporary Bartoli "poured scorn on this theory in Del suono de'
tremori e dell'udito (Rome 1679). Since then no theory has been
propounded."
Abbot Gattoni of Milan in 1783 and H.C.Koch in 1801 experimented with
various string metals and examined the conditions which produced
Aeolian tones. Pellisov quantified the findings of Gattoni and Koch
in 1822. V. Stouhal of urzburg (no date given) empirically proved
that the frequency of any one Aeolian tone was not dependent on the
material or length of the string, but was equal to the product of the
airstream speed a distance from the string and a constant (normally
0.185, known as the Strouhal number) divided by the string diameter.
Strouhal's theory depends on the string vibrating in the same place in
the airstream.
Rayleigh, using a telescope to examine a string stretched under his
chimney, claimed the string vibrated across the airstream. Further
researches by E. G. Richards on and more recently by Etkin and others
in America have only feebly penetrated the problem. (Note: When the
phrase 'feebly penetrated' is used, it is desireable to be designated
as an 'other'.) Present theory suggests that eddies create a vortex
pattern behind the string to make the Aeolian tone. When these eddies
are the same pitch as the string's natural frequency, they cause the
string to vibrate. An exact solution of the creation of these
vortices and their resultant pattern, termed 'Karman Street' (after
von Karman 1912) appears to be beyond the capability of present
mathematical techniques.
How to build the bloody thing. Aeolian harps have traditionally been
boxes with equal length strings parallel to the soundbox. This, the
^C}ko-here seems no reason why other configurations shouldn't work as
well or better. Can results be achieved using strings which are not
parallel to the soundboard? Are the traditional dimensions necessary?
How can you keep rain out of the soundhole?
Modrn materials should work better than the conventional thin wooden
structure with brass or gut strings, at least with regard to
durability. Kastner in 1856 commented that "Harps that maintain
themselves in a decent state in teh garden have long been sought
after." The rapid deterioration of Aeolian harps made of traditional
materials is the main cause of their disappearance for the scene. An
Aeolian harp which lasts a generation could become as common a garden
fixture as the gazing globe. Maybe plastic is the future after all!
Sheet metal! Formica! Graphite! Kevlar!
Aeolian harps traditionally have 4 to 12 strings of catgut or brass of
equal length and unequal thickness, but they have been made with 24
and 48 strings. These strings stretched over two hardwood bridges of
triangular cross-section, mounted on a thin pine, maple or mahogany
box of variable size and shape, ranging from 75-200 centimeters long
(normally 85-110 centimeters), 11-35 centimeters wide (normally 12-26
centimeters), and 5-17 centimeters (normally 5-9 centimeters) deep.
The strings were parallel to the surface of the soundbox. The ends of
the soundbox may be hardwood for inserting iron hitch-pins or wooden
tuning-pegs. Most instrument have some device (wings, vanes) for
concentrating the wind on the strings.
Historically tehere were six basic forms of Aeolian Harp.
1) The simplest. A rectangualr soundbox with a single horizontal row
of strings.
2) Similar to1 but designed for use in a sash window. Heere the
strings are mounted on an inclined fingerboard with a lid which
fullenls the air over the strings.
3) A vertically strung soundbox with wind funnelling 'wings' or vanes.
Developed by Kicher in Rome in 1650.
4)The same as 3 except that there is a bank of string on each of the
two sides of the instrument with the vanes funnelling the wind past
both sets of strings. In this model, the strings are always in the
plane of the wind direction.
5) In this type, strings are set in a semi-circular soundbox so that
at least one or two strings will always present themselves at the
correct angle regardless of wind direction. This description is not
entirely clear to me and Grove provides no illustration. This is an
ideal situation for someone trying to develop a new concept. :-)
6) In this, a variant of 5, a semi-circular model consisting of a
triangular soundbox mounted with strings on two or three faces.
That's all there is. Get out there and build. What an opportunity to
make something that will annoy your neighbors more than windchimes!
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I've been trying to send this for a couple of weeks but Gremlins keep
attacking my net server.
Ed Margerum
emargerum@mecn.mass.edu