Yes, great topic - I also stumbled onto the same Tobias article Sunday afternoon. I was concerned about this enough a few months ago that for a while I considered not having any accent laminates in the body, and maybe not even a back laminate (though I decided to have both).
I have a hard time believing the glue joint itself is really an issue, unless maybe you get way too many of them. Unless you're using something like rubber cement, a properly executed glue joint (no gaps, minimal glue, lots of clamping pressure, etc.) should mostly just bond the pieces of wood, and not be thick enough to have much in the way of its own characteristics. Besides, you're usually stuck with a bunch of these anyway: multi-piece necks, fretboard glued to neck, body wings to through-neck, etc., and no one seems to be too worried about that.
It seems to me the issue with set necks and bolt-ons is a bit different, not so much a matter of the glue itself but rather the fact that you have a joint there at all, and it just isn't going to be as rigid and consistent as a continuous piece(s) of wood, plus in most cases it's joining different types of woods with different resonant characteristics.
Certainly Alembic works hard to keep the energy in the strings, which is generally good because these things are definitely not acoustic instruments. The thing I'm most curious about is how much vibration manages to make its way from the strings, through the bridge/bridge block into the body, and then back again into the strings. I'm convinced the answer is some, but it may not be very much (at least with the Alembic approach).
Suppose you took this to an extreme, and built a one piece neck/bridge/nut sculpted out of a piece of polished granite or something similar - extremely massive, almost entirely non-resonant. This would pretty much keep as much energy as possible in the strings, but I have a feeling it wouldn't sound right. It would probably need some extra flavor, from the body wood either emphasizing, or hiding, some combination of frequencies.
So, let's assume for a moment that some energy goes through the bridge and gets soaked up by the body wood (not returned to the strings at all). It seems that the biggest factor here is the mass/density of the wood - really heavy stuff like ebony isn't going to absorb the lows like a lightweight piece of ash, for example. There may be some subtle differences between tone woods of similar weights, possibly due to grain structure or something, but most descriptions I've heard or read generally track pretty well with the density (remember, we're talking about solid bodies here - grain structure is very important in acoustic instruments, but that's a different problem).
An advantage of sandwiching different woods could be that it helps to spread out the absorption characteristics, or equivalently, the resonances of the body - if the body resonates strongly at frequency X, then it saps that frequency from the string (unless it manages to put it back into the string, which I'm ignoring for the moment). Assuming you want a full, even mix of frequencies, or at least no major gaps, then a variety of woods might be good.
Does the ordering of the layers matter? For the sake of argument, let's assume the bridge block is anchored in the core wood, and that you have fairly thick front and back laminates such that together they add up to the core thickness. My guess is that an ebony core with ash laminates would sound different than an ash core covered in ebony - even though in this model the total mass of the body would be equivalent. (I really don't know, this is just what my gut tells me.)
In other words, I can imagine that each layer of wood would act as a filter for certain frequencies, and might thereby negate the benefits you would expect from some subsequent layer; the more layers you have, the more difficult it would be to predict the outcome (although maybe a bunch of very thin layers would matter less than a few thick ones).
Finally, suppose that some of the body vibrations actually do get returned to the strings. Even on an Alembic, you can feel the body vibrating, and I believe I can distinguish the frequencies (to a limited degree) I feel in the wood when playing different open strings. It seems like some of this is going to continue to affect what the strings are actually doing. If so, then energy at some frequency has to find its way from the string, through the bridge/block, into the core, out through the various laminates, and then all the way through the reverse path to get back to the strings. This is when I would be more worried about the complications of multiple layers, but perhaps this effect is negligible. I sure wish I knew...
I forget which month it was, but as I recall Wayne had a featured custom in which he used coco bolo for accent laminates, just to make sure some of that wood was in the mix - so does it matter in which order you add the ingredients, or is it just the total recipe that counts?
When I eventually get my bass, one of the things I plan to do is experiment with bridge blocks made of a few different types of wood, in addition to the big chunk of brass. Won't really address the hippie sandwich question, and certainly will be a bit of a nuisance, but I expect it to be quite interesting - does anyone else have experience with this?
-Bob
