The sound holes can have different shapes: round in flat-top guitars, G-holes in instruments from the violin or viol families and in arched-top guitars, rosettes in lutes. Bowed Lyras have D-holes and Mandolins may have square or triangular holes. A round or oval hole is usually a triple one, under the strings. G-holes and D-holes are usually made in groups of three placed symmetrically on both sides of the strings.
Though the purpose of sound holes is to help acoustic instruments project their sound more efficiently, the sound does not emanate solely (nor even mostly) from the location of the sound hole. The majority of sound emanates from the surface area of both sounding boards, with sound holes playing a part by allowing the sounding boards to vibrate more freely, and by allowing some of the vibrations which have been set in motion inside the instrument to travel outside the instrument.
Some Ovation stringed instruments feature a unique soundhole design with multiple smaller soundholes that, being combined with a composite arch-top guitar body are said to produce a clear and bright sound.
Tacoma Guitars has developed a unique "paisley" soundhole placed on the left side of the upper bout of their "Wing Series" guitars. This is a relatively low-stress area that requires less bracing to support the hole.