Why the sound holes on violins and
arch-top guitars are "f" shaped, and the sound
holes on flat-top guitars are round.
The main considerations when looking at the
sound-holes in guitars and violins are their
shape, size and position. Guitars with round
sound-holes are different instruments from those
with "f"-shaped sound-holes.
The fundamental problem with guitars is that the
stresses of the strings distort the instrument by
both bending and twisting it. Flat-topped
guitars--typically Spanish (or classical),
flamenco and folk guitars--have round
sound-holes. They are lightly built and usually
have gut or nylon strings. Distortion of the body
is prevented by bracing structures around the
inside of the soundhole. In these guitars, a round
sound-hole offers the best structural solution
while giving the best projection and volume.
Most flat-topped guitars are based on the designs
of Antonio de Torres Jurado, a famous
19th-century guitar maker. However, there is an
alternative to this type of guitar. The Ovation
guitar has 11 small holes at each side near the
neck rather than one central round sound-hole.
These holes eliminate feedback if the guitar has
an acoustic microphone.
The arch-top guitars with "f" holes use metal
strings, are of heavier build, and do not have the
tonal qualities or projection of flat-top guitars.
This is because in the past, these guitars were
mainly rhythm instruments that were thumped
rather than played. The "f"-shaped sound-holes
allow a solid strut to extend the length of the
guitar body, giving it the necessary strength.
However, this changed when electric guitars took
over from standard acoustic ones. Electric guitars
have electronic sound pickups instead of
sound-holes. The body of an electric guitar must
be rigid, because vibration will distort the sound.
When a guitar is played electrically sound-holes
serve no useful purpose.
Some players, typically jazz musicians, prefer the
semi-acoustic guitar, which has both pickups and
"f" holes. These can be practised on acoustically
yet performances can be amplified electronically.
These guitars obviously still require the
sound-hole. However, the overall trend is
towards solid guitars which have no holes.
Violins do not have the option of a round
sound-hole, as the pressure the musician places
on the bridge while holding the instrument would
be likely to distort the body if it had a central
hole. The violin also requires internal bracing
that is better offered by the "f"-hole design.
Some string instruments like the banjo have the
sound-hole at the back. The one-string fiddle
has no body, but uses a horn and diaphragm.
As for the appearance of the "f"-shaped design,
this is probably related to the musical character
for fortissimo, rather than any acoustic benefit.
Source: The NewScientist - LastWord