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The efficiency of sound radiation
at low frequencies in musical instruments is improved by use of a sound
hole. The sound hole enhances the radiation of sound by vibrating the volume
of air in and near its opening. A common example is an empty bottle: the
air inside vibrates when you blow across the top, and enhances the radiated
sound. This phenomenon, called the
Helmholtz resonance, is utilized in musical instruments to enhance the
radiation of sound at low frequencies.
An important characteristic of
the sound-hole is the frequency at which the radiated sound is enhanced
most. This frequency, called the resonance frequency, can easily be obtained
for holes with simple geometries such as the circular hole in guitar (see
The Theory of Sound, vol. 2 by Lord Rayleigh). For the sound holes with
complicated shapes such as f-holes or
lute rosettes (See below), finding the resonance characteristics is much
more challenging.
We analyzed the resonance
characteristics of different lute rosettes.
In collaboration with
VRFL group, we have developed a method to analyze the resonance
characteristics of complicated sound holes such as the ones shown above.
Using our method, we have provided answers to questions involved in the
effect of shape, orientation and location of sound holes in different
musical instruments.
The developed method has been
verified by measuring the resonance and bandwidth of different openings on a
standard resonance box (see Fig below)
Killian Court (MIT)
October 18th 2008, 2:00 am!
 
The velocity profiles.
Using the
method developed, we have investigated the characteristics of f-hole for all
the instruments in violin family. Thanks to
Johnson String Instrument we had the chance to verify our results
experimentally.
Running the test on a double bass
at
Johnson String Instruments.
Running the test on
Andreas Berr lute,
a 17th Century
Lute at the
Museum of Fine Arts (Boston)
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