I am a layman when it comes to physics, but here goes it as I understand it: Body resonance plays a huge part in sustain as well. Resonant frequency can be manipulated by changing stiffness (neck woods, etcetera) and changing mass (heavy body, bridge block). At the resonant frequency, or one of it's harmonics, the energy of the string is absorbed (by moving the body or neck) very quickly and efficiently. Try playing the 7th fret on nearly any bass (even most Alembics) and you'll hear a faster decay than on the notes above and below. Now clamp a C-clamp on the headstock (not of your Alembic though) and you'll find that the dead spot moves and maybe disappears altogether. It's an old trick to get rid of dead spots on Fenders when recording. I also seem to recall a company marketing brass plates that went on the back of the head under the tuners in lieu of the unfashionable C-clamp. With a stiff neck alone, the energy will be quickly used to vibrate the neck because of the neck's low inertia (it is easier to put into motion because it's relatively light). The big body of the Alembic has a lot of inertia and doesn't soak up the string's energy as quickly. String tension makes a big difference on resonance, with 35 and 36 inch scales (all other things being equal) having better fundamental sustain. They make the neck behave as though it's stiffer because of the increased tautness of the string for a given pitch. It's a lot more critical as the mass of the string increases as well. I believe the deal with very light basses achieving good sustain is that the resonant frequency has been moved outside of the fundamental range in the other direction. Resonance is why bolt-ons and set-necks are more mid-rangy than neck throughs, and why we (the royal we, that is) wish we had purpleheart and ebony neck-throughs like Rami...
John
