The mode animations in this section are extremely amplified depictions of the way the soundboard of the guitar vibrates at certain frequencies.
This information is important to the guitar maker as the frequency distribution of these modes of vibration over the range of notes on the fingerboard and beyond, dictate the overall image of the sound for any particular instrument. Only some of the lower order modes have been included here of which all are excited by notes of the frequencies found on the fingerboard.
The modes are just that, modes of vibration which occur at given frequencies according to the local stiffness of the soundboard. One of the guitar makers goals is to identify and learn how to control the frequency and width of the modes to be able to manipulate to some extent, the overall character and refinement of the guitar. Some makers have disputed that this is even achievable, but this is something that violin makers have been utilising for hundreds of years and also used routinely by Jeff in his construction in a slightly different way. This is perhaps best utilised to act as a visual guide or benchmark to help obtain consistency of sound.
There are several methods of exciting the modes including simply damping and tapping the soundboard in selected patterns to excite one mode while damping the others through to driving the soundboard with a function generator through a small voicecoil and driver. Modes can be either revealed with the application of some sawdust or glitter etc or by plotting the sound radiation picked up from a nearby microphone. There is also a method of photographing these modes by using ‘holographic interferometry’
This information is supplied to give a brief overview of the modes and what they mean to the guitar maker.