This shaping of the wood is known as "resonance plate tuning" (or "plate tuning"). It refers to a comprehensive tuning of the wood and bracing (its density, thickness, tension, sound-influence) to influence the acoustic properties. It does not refer to a tuning of the guitar-body to a single "default" frequency. Instead, it is a comprehensive way of shaping the wood and its response and resonance properties to improve the guitar's sound.
The "tuning" of the wood is also called "voicing" the instrument. The techniques used trace to previous centuries, especially in violin-making (example: attempt at understanding some of the tuning schemes of Italian violins: 1, 2). Some guitarmakers believe that the actual voicing of the wood, and working with and "shaping" the wood (during and even after construction) is more important than the outer construction itself (such as chosen bracing): "As my skill and experience have grown I have come to believe that what makes a good guitar good is firstly how well fine tuned and balanced it is rather than what type of strutting system it is built with. Different strutting systems can add different flavours to the sound but is never the main factor in the Good Guitar."
One of the important aspects that good luthiers need to understand, is that a single tone consists of the "fundamental and simultaneous overtones".[10] (Historically the scientific analysis of this discovery can be associated with Nicole Oresme, Marin Mersenne and Joseph Sauveur.) The ratio of the "intensity of fundamental" and the various overtones, defines the "colour" (Frequency spectrum) of the tone. Overtones are simply frequencies that are at a multiple of the base fundamental frequency. (Overtones defining colour, do not only occur in instruments, but also in the human voice. When singing a note, there are numerous overtones present.
Singers experienced in overtone singing are able to control their voice in such a way, that they can increase the intensity of any high overtone to such an extent, that it becomes clearly audible, whilst simultaneously singing the fundamental. In this way two pitches (fund Tonal colour is an important characteristic on a guitar. Usually the notes of the guitar's different registers (low bass, mid-range, high, etc.) have different colour-spectrums, i.e., differing relative intensities of fundamental to different overtones.
Various types of guitars have tone-differences in the various registers (also differences in response, action, etc.). Specific colour-spectrum characteristics of certain types of guitars can be said to form a specific "sound aesthetic"—this is like a "fingerprint" of the characteristic of that type of guitar. Other guitars have a different "sound aesthetic", i.e., a different colour-spectrum characteristic. Different historic instruments reflect various sound aesthetics.amental and high-intensity overtone) can be made clearly audible while singing.)