While the back and side woods of an instrument do vibrate, their major role is as the reflecting surface for the sound waves transmitted by the top. Mahogany tends to be softer than rosewoods and produce a very clean crisp tone. Rosewoods contain more natural oils and are bassier, boomier and more robust than mahogany. I often liken mahogany sound to a tart lemony flavor, and rosewoods to a good dark chocolate. Koa and walnut will fall somewhere in between the two. However, there is so much variation from piece to piece even within the same species or even the same tree that it is very difficult to generalize. We have had many pickers at Maple Leaf who walk in the door swearing they will only play a rosewood guitar and then walk out with a Huss & Dalton or Froggy Bottom mahogany.
The very best plan of action when deciding which back and side woods are best for you is to play lots of guitars, both new and used.
Here are our pages describing the most commonly used back and sides woods: