Acoustic guitar body styles and sounds
Martin D series. This is the ubiquitous acoustic guitar. Used in the 60s folk boom and in bluegrass. Full low end and clear high mids. Takes some digging in to activate the strings, but easier to play aggressively. Great for strumming and flat-picking.
Martin OOO and OM. The names auditorium and orchestra are sometimes used interchangeably. Tend to have a midrange scoop, especially Taylors. The orchestra is a little bigger, has a little more midrange, and was used famously by Eric Clapton in his unplugged sessions. These are tonally between a dreadnought and a concert. Lots of versatility and great for strumming.
Martin OO. Woody Guthrie and Bob Dylan played concert guitars. Narrower than a dreadnought and more comfortable to play seated. Less midrange and well-suited for singer-songwriters. Quieter and ideally suited for finger-picking and melodic playing.
Smaller than a Martin O size (though some Martin Os are called parlor guitars). They produce more volume when played lightly than what a dreadnought would produce. Less bass and more mid and high range. Quiet and ideal for finger-picking. Used prominently by folk and blues artists.^[ 7 Acoustic Guitar Body Shapes, Their Differences and Sounds | Reverb]