Concert, or Model “O”
“They are slightly larger in size than the parlor, and are also suited well for fingerpicking.
Grand Concert, or Model “OO”
The Grand Concert was derived from the shape of the classical guitar, after it was standardized by the work of Antonio Torres. Its one of the quietest model of acoustic guitar. It has a solid mid-range register, so that it is a great all-around guitar. Gives you better access to the higher frets.
Orchestra Model, Grand Auditorium, or Model “OM” or “GA”
This model is also sometimes called an Auditorium or “OOO”. It is a mid-size guitar, with great balance, volume, and projection.More treble on the tonal side.