Sorry but theres too much nonsense in this post. If you study the physical phenomenon of "resonance" you understand that the snake oil thats trying to be sold here is that somehow the resonant frequency of a particular wood can match the resonance frequency of a guitar string (and in most cases 6 different guitar strings at 22-24 different fret positions). The problem is the while the resonant frequency of the wood remains constant, each string (and each string played on each individual fret) will have its own unique resonant frequency, which means that even if you achieve "in-time" resonant frequency ie. pushing someone on a swing at just the right point to maximize (or at the least, increase) amplitude or getting that perfect double-bounce on a trampoline, it would mean that it would work on that particular string's resonant frequency only. And as mentioned earlier, because the wood's resonant frequency is more-or-less constant, it would mean that an in-time RF on one string (or one note) could mean an off-time resonant frequency on another string/note. Thus, if wood and its resonant frequency really had a meaningful impact on sustain, it would be an absolute headache. Other factors such as string length (scale length) or length of the string when played on a certain fret for instance has a much greater impact on sustain. (Its why its hard to get a note to ring out on the 22nd fret as opposed to an open string). It would take a technological revelation in wood for it to be able to modify its resonant frequency to match the note being played so that all notes have increased sustain. Woods having an impact on "tone" is a much more nuanced debate but the argument for longer sustain is one that's cut and dry mythbusted for me.