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

Minor point about banjos: Saying they "have the sound-hole at the back" is missing quite a lot. Decent modern banjos usually are not open in the back. They have a resonator, a kind of rounded wooden shell covering the back. There are sound holes all around the outside rim of the resonator, facing forwards. But the main thing about a banjo, with regards to its sonic archictecture, is that the bridge is held tight against a drum head by the strings. The vibration of the strings is transmitted directly to the head of a drum. This is quite a lot different than just having a sound hole, and is what gives the banjo its characteristic sound, a rapid attack and very very swift decay with very little sustain for a plucked stringed instrument.

The other thing I've wondered is just exactly what sound holes are for. The name "sound hole" I believe is misleading. It's not necessary to have a hole to "let the sound out" as it were. After all, the bridge transmits the vibrations of the strings to the thin wood surface of the violin body or the guitar top or a banjo's drum head, or whatever. The point is, the vibrations are transmitted to some kind of "tympanic membrane" that can move some air. I think the "soundholes" are more along the lines of the ports in bass reflex speakers. Well, maybe in simple terms, the ports in bass reflex speakers are there to "let the sound out." But in this last paragraph, I'm just speculating.

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