Banjos were a popular instrument in the 1920’s because they were loud. Guitars were replacing banjos in popular music and some banjo players were switching to guitar. If you were a banjo player you were used to having all frets clear from the body. Guitars at the time, still based on classical and Martin designs, all had the neck join the body at the 12th fret or half the scale length. This gave a full octave playable on each string before the neck reached the body.
Perry Bechtel, a banjo player, came to Martin and asked that they make a guitar where the neck joined the body at the 15th fret. This would make it more familiar and appealing to banjo players. Martin compromised and made a guitar where the neck joined the body at the 14th fret. They named the new model the Orchestra Model.
So how did they accomplish this. They modified two design features to add the two extra frets. First, they made the body length a bit shorter. You can see this in the following table (note the table is from current specifications on the Martin website and not the dimensions of 1929 guitars). Then they moved the location of the bridge (and thus the neck) so it was farther from the end pin. Ta Da! A 14 fret guitar.
|12 Fret Body Length
|14 Fret Body Length
|OOO or OM
I own a Martin OM-28, the direct descendant of this innovation. This changed spread quickly and within a few years almost all guitar manufacturers 1 were making guitars with 14 fret neck joins – often eliminating the 12-fret models.
Was it a good change? Certainly the 14 fret join is the most popular style of steel string acoustic guitar. But a few finger style players believe that the bridge is no longer in the “sweet spot” of the guitar body and thus doesn’t sound as good. Also, the smaller body reduces the volume of air and affects the sound. This is part of the reason why 12 fret models as well as 13 fret compromise guitars have become popular among many finger style players.
One of the promoters of the 12-fret OM design is. He has designed guitars for Martin, designs and sells his own guitars and collaborated with others. currently has a Schoenberg model.
Martin 000 12-Fret (left) and Martin 14-Fret OM-21 (right). Notice how the body shape is flatter on the 14-fret guitar (right) near the neck where the length has been shortened compared to the 12-fret guitar on the left.