Guitars come in many sizes and shapes but over the last century they have become somewhat standardized and the shape of a guitar is instantly recognizable and iconic. A guitar could be built that looks like a triangle, square, watermelon or whatever, but we would not expect it to have the sound we have become accustomed to as a guitar sound. A banjo works on the same principal as a guitar, but it doesn’t sound anything like one. So shape and size do matter, but if it is generally close to the accepted guitar shape and material, the difference is somewhat subtle. We can make some generalizations about size and shape, but they can all be undone by other aspects of the guitar such as hole size or bracing or top stiffness or a lot of other factors.
From the smallest guitar to the largest jumbo guitar, they do not vary more than about 3” across at the lower bout and the great majority of guitars fall within an inch either side of 15” across the lower bout. The length of the body is similarly within a fairly narrow range, usually within an inch either side of 19” in length. Guitar depths are wedge shaped to prevent standing waves. Customarily being deepest in the tail of the guitar. They generally are between 4” – 5” in depth with the majority around 4 1/2”.
Martin Dreadnought Gibson Slope Shoulder 00 OM Cutaway
Intuitively we might believe that a larger body might be louder or have more bass response. That is partially true if one compares the extremes of the guitars from the smallest to the largest. The differences between guitars hovering around the average size are much more subtle. In my experience, the dreadnought size tends to have a little more bass response and the medium body sizes tend to have a more balanced response. I’ve also found that the medium sizes can be just as loud as the dreadnought sizes.
In some cases, body shapes are chosen more for historical reasons. Most flatpickers tend to favor a dreadnought style and most finger style or folk players tend to favor a medium body size. There are always exceptions of course, I believe that some of the early James Taylor finger style playing was on a large body Gibson J45 and Eric Clapton has an Orchestra Model (medium body size) named after him.
Those who like to play above the 12th or 14th fret may consider adding a cutaway. Since the upper bout of the guitar is rather heavily braced to support the neck loading it does not greatly contribute to the guitar’s sound. I have not detected a discernible difference to tone by adding a cutaway although they do require additional building time and fitting.
It appears to me that everything about a guitar affects the other aspects of the guitar. Body size and shape is just one of the factors. Other factors such as scale length, number of frets clear of the body and wood choices are equally important.
The bottom line is pick a body shape that fits your body size, is comfortable to play and is aesthetically pleasing to you. Your luthier should be able to help you with some of the other decisions to get the most out of it.
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