Round sound holes centered near the waist of acoustic guitars have been the standard since before Torres. The main alternative we’re all familiar with are the f holes of archtop guitars, borrowed by Gibson from the design of orchestral stringed instruments. But why have holes at all? Do we need them for the sound to get out? Not exactly. Most of the sound comes from the top of the guitar. If you block the sound hole, there is only a slight change in the sound.
The answer is complex and involves physics. Physics is not my area of expertise but my layman’s understanding is essentially that the air movement inside the guitar can either deaden or reinforce the vibrations of the top. The size, shape and placement of the sound hold can thus effect wolf tones, clarity and balance. Larger sized holes can increase mid tones. But perhaps the most important things to remember is this is a complex topic; luthiers experiment more by instinct or trial and error than by physics; and in the end the results are subjective. Do you like the sound?
I think the physics of guitars is interesting but for the most part, I’m going to just review some of the variations in sound hole design that are being used today. A good review of sound hole alternatives was published in Acoustic Guitar in 1999 is reproduced at that authors website.
Standard round holes
The size and shape and location of the guitar sound hole has been fairly constant for hundreds of years. The classical guitar shown here is typical of classical and steel string acoustic guitars.
Larger than standard sized holes
Enlarging the sound hole can reduce the wolf tones and make for a better recording guitar Tony Rice is one of the artists who endorses this concept. Martin has made a “D” sized guitar with this feature. It’s designation is the HD-16R LSH. The “LSH” stands for “Large Sound Hole”.
Gibson invented the archtop guitar and soon after that added f holes to that design. You can still buy archtop hollow body guitars with f holes but if you want a purely acoustic instrument there are fewer choices. Godin, The Loar and others make affordable, non-cutaway f hole guitars but all acoustic f hole models (no pick ups) are rarer now days. The image below is the Gibson ES-150 also known as the Charlie Christian model.
There are two popular variations of the guitars favored for Gypsy jazz guitar. Among the most noticeable differences are the shape of the sound hole. The guitar pictured below has a small length-wise oriented oval sound hole. This is referred to as the Petite Bouche or “small mouth”. This design was originally made by the Selmer company and made famous as the guitar played by Django Reinhardt.
I remember Pete Segar played a guitar with an odd, almost triangular sound hole. Gretsch has made several acoustic guitars with a similar sound hole. Below is one of their Rancher models which is still available.
Ovation was one of the first guitar makers to experiment with offset sound holes. These originally appeared in their Adamas carbon fiber topped line. Ovation (now owned by Fender) still has guitars and mandolins with epaulets over multiple sound holes.
Sound holes in the side of the guitar instead of, or more likely in addition to holes in the top are another feature that is gaining popularity. Luthier Alan Curruth has experimented with side ports. It is unclear if the sound heard by an audience is improved or not with side ports, but the clear advantage of side ports in acoustic instruments is they serve as a personal monitor allowing the instrument player to better hear what they play.
I couldn’t find any big online retailers selling acoustic guitars with side ports but these are also seen on ukuleles from Riptide (and other more expensive makes). Riptide is made by Boulder Creek who also makes guitars with side ports – too bad the online merchants don’t carry their guitars.
More Examples of Sound Hole and Port Design can be found on my Pinterest Board “Sound Holes and Ports“.