The material and mass distribution of a guitar's body drastically shape its tone. In this section I reference the fundamental and harmonic frequencies. The former is the perceived pitch that is heard when a note is played. In actuality, there are many more harmonic frequencies related to the fundamental that are sounded simultaneously. They are what give a sound its timbre. If all a guitar would produce was the fundamental frequency, it would sound like a sine wave, and that's not a very good guitar tone. The various materials, parts and methods of construction used on a guitar push and pull on each other and produce a unique set of harmonic frequencies that are part of its tone. This is known as timbre, but is popularly refered to as "tone" by guitar nuts like myself.

The popular title "tone woods" is given to those that are commonly used to make instruments. Whether or not these contribute to "good tone" are up to their interaction with the rest of a guitar's components as well as your own taste. The following is a list of some of the most popular tone woods and their tonal qualities.

Mahogany is a very pretty, dark to light golden-brown wood used for bodies and, less often, necks. There are many different types of mahogany, but they all have a uniform density, open grain and large pores. It accentuates bass and low-mid frequencies, and cuts high-mids a bit resulting in what some call a "nasal" sound. In my experience, this wood produces a fat sound with nice harmonic overtones. Gibson Les Pauls are often made of mahogany.

This is the classic Stratocaster tone wood. It has inconsistent density between its rings with soft pockets scattered throughout, giving it an even frequency response with scattered drops in the mid frequencies. Different cuts of Swamp Ash are likely to sound different from each other due to the varying abundance of soft spots. Cuts that are from further up on the tree have a more uniform density and generally get the same mid frequency dips. This creates the perception of less exciting harmonics and bass. Usually, heavier pieces of swamp ash sound dull, and lighter pieces sound more alive.

This wood is soft and has tight pores, which make it very economical to build guitars with. It has a very pronounced mid range, which is good for cutting through a mix. If you want a complex timbre, however, basswood is terrible. It has muted highs and barely any bass.

Similer to basswood, but retains more highs and lows, so its sound is a little more complex.

This is a very hard wood and makes for pronounced upper-mids and highs. The low end isn't left behind, though. Using other components that accentuate the bass frequencies produces a very tight bass sound.

There is a great sonic difference between guitar bodies that are solid and those that have hollowed out cavities within them. It is hard to find the right words to describe the difference other than saying that a hollow body simply sounds hollow. Solid bodies resonate in a very controlled way that is more conducive to high gain amplifiers. Hollow body electrics may feed back when amplified to very high levels and usually sound brittle through a high gain amp.

It is my theory that the shape of a guitar affects its tone based on its total amount of mass and its distribution in space. Obviously the wood at the center of the body between (and surrounding) the neck and the bridge are the most important, because that is where the strings are transfering their energy into the body. However, vibrations spread throughout the entire body and "bounce around" between all of it's extremities.

This concept is illustrated if you take a plate, cover it with a thin layer of sand and then use a violin bow on the plate to set it vibrating. The grains of sand will be bounced onto the nodes (points at which there is no vibration), showing how those sonic vibrations move through the plate. Different shaped plates produce different vibrations and different patterns in the sand.