Guitars, like other musical instruments, display several distinct resonances that are important determinants in the sound of the instrument. These resonances occur at different frequencies and, interestingly, have unique shapes that usually appear in a predictable pattern as one progresses from low to high frequencies (or low to high notes, to use musical terminology). The behavior of the resonances is complex and is not especially well understood by physicists, particularly in regard to the question of what makes a great guitar. Nevertheless, I have found resonances to be a very useful tool for improving and giving consistency to my instruments. Dealing with wolf notes, dead notes, and issues such as balance, power, and timbre, plus many others, are all made much easier with a knowledge of...