As the sound from a guitar is mainly radiated from its vibrating surfaces, the variations in sound between different guitars and between different types of guitar are due primarily to the size, shape, amplitude and natural frequency of the various modes. To alter the sound of a guitar it is necessary to alter the size, shape, amplitude or natural frequency of a mode or modes. Because guitars have a generic tendency to vibrate in certain ways, it requires quite a significant change in the bracing structure to precipitate a change in the shape or amplitude of a mode. Changing a mode’s frequency is a little easier.
Learning how to manipulate the parameters of the modes and, in particular, understanding what the target frequencies should be has been the focus of my research and development efforts over the last 10 years.