English is not my native, but i'll try adding my pinch of vodoo partial interpretation of physics.
Of course, energy can be absorbed, dissipated, or resonating, partially gived back. The point is in the last part. How can a structure give back some of his energy. Low frequency content is barely hearable since humain earing is not so much sensitive in low frequency range. So a low energy content, will (mostly) be restored in some faster energy content/higher pitch, when a solid resonate. A complex energy frequency content will add some intermodulation content. What the hell do i am talking ? It's all about harmonics. Harmonic of low frequency content allow us/human to reconize the original frequency. There's lot of talk about "the missing fundamental". Harmonic content is that shaging stuff that make a triode amp sound so warm. Some prefer triode sound, some penthode....etc...there some more or less typical signatures. It's all as with photos, saturating some colors/changing exposure, contrast, luminosity, adding blur effect... It's always the same photo, but there's lot of small parameters that will affect our subtil satisfaction.
About wood. maple is not the same as another maple. Depending of where/how the wood has grown, it parameter chimical and physical varies. Stradivarius took is wood in a forest where wood took lot of silice => less aborption, a bit more weight.
Back to subject, carbon, for exemple, has very low absorption coefficient, and high stifness (Aluminium has more/less same stiffness, but higher absorption, and is denser) So it will give back lot of energy. But here, we don't have yet talk about constraint put to a neck. To simplify a looooot, the more flexion constraint we add a structure, the less it can generate higher order harmonic. Again, what the hell ??
If string tension of a instrument is maintained by external structure, there is less harmonics generated by the instrument, AND more absorption. Why more absorption ? The more a structure is stressed, the more it become rigid.
So is there so many difference between a very rigid neck, or a soft wood neck compensated more by the truss rod ? Loose car supension does no more absorb energy, it give it back..
Weight. Weight add another parameter. depending of it weight, dimension, a structure has it own resonnance frequency. It will resonate more or less depending of the frequency.
Same rigidity can lead to different energy absorption. It's just how structurally "movement" is converted in heat. There's lot of papers about it. Kevlar, for is rigidity, absorb a lot energy. Balsa is funny depending the axe of fibers, does not absorb a lot in compression, but a lot perpendicular to fiber. That funny seeing wrong orientation of double top guitar with balsa wood with fibers of balsa oriented in the same side of tables leading...
Then we read a normal speaker frequency curve, we read in reality the level of sound generated for each frequency sent to the speaker. For exemple we can get 110 db at a frequency of 50hz generated by agenerator. But in reality a fft analyser will telle use we in fact got only 106db produced at 50hz, plus lot of harmonics. The speaker in itsef generate lot of hamonics.
And the worst since is that we mostly ear at environnement resonnances...I won't get into, but there's a lot to say too...
There's lot of thesis and paper about all of that, and some go far in instrument construction. A lot of stuff can be found looking at speaker science. But lacking of true mathematical basis, all i managed, is to convert it to this poopy vodoo ideas.
