Here's another vote for humidity changes as being the culprit here. I live in Delaware, in the the Mid-Atlantic region of the USA. According to my home weather station (ok, I admit it, I am a weather geek) the relative humidity in my house has ranged from 5% to 61% this year. That's a lot of moisture soaking into, and being sucked out of, the cells that make of the wood in my basses!
Roger, you mentioned that your house is centrally heated, which is great for human comfort and awful for basses. Forced air heat is particularly awful as the relative humidity of air will drop when it is heated (assuming that your heater, like most) is not designed to add moisture in the process). It is common for the relative humidity in a building with forced air heat to hover in range of 20% - 30%. Contrast that with average relative humidity in London, which ranges from the 70% -75% or more in the winter to 55-65% in the summer. The swing between indoor (central heat) humidity and outdoor (real) humidity is often most problematic in the spring, when we begin to open our windows and let the outside air inside. Your basses have been living in dry air (perhaps 25%-30% relative humidity all winter long, and all of a sudden the air becomes moist (55%-60% RH). That's why I call the spring truss rod time. Similar problems can crop up in the summer if you live in a part of the world that is influenced by maritime air (which is quite moist) and where central air conditioning is common (like the US East and Gulf coasts), especially if you keep you basses inside where it is cool and dry and sometimes gig outdoors where the relative humidity is quite high.
Are Alembics more susceptible to neck movement than some other basses as a consequence of seasonal changes in humidity? In my experience, the answer is yes, but to a very minor degree. Every season I need to tweak my truss rods by perhaps 1/4 to 1/2 a turn, but NEVER MORE THAN THAT. I have some other basses that don't seem to move at all. I have no idea why that is so, but to me it is a big so what because the process of tweaking the truss rod takes me maybe 5 mintues twice a year. Once I make the seasonal adjustments (at the beginning and end of the heating season) my Alembics are very, very stable throughout the year (unless I play an outside gig in the very humid summer months).
However, that's really not the issue here. I have found one is more likely to notice fret buzzes as a consequence of a little bit of neck movement due to seasonal humidity swings on an Alembic because they are so well built that it's possible to set them up with much lower action than other basses will tolerate, and that's what we often do.
If you set your basses up with a standard amount of relief (say, .015 as measured at the 9th fret) and medium action (say, 3/16 on the B or E string at the 24th fret) you may never notice the relatively small changes in neck relief due seasonal humidity swings. If you like lower action than that, or less neck relief (i.e. Entwistle action) you will notice the buzzes caused by humidity changes, but it's also true that most basses (other than Alembics) are not capable of action that low in the first place.
It's kind of a one of those good news/bad news dichotomies...the good news is that Alembics are capable of super-low action, and the bad news is that set-ups with super-low action are more likely to require regular maintenance as a result of seasonal changes in humidity. I'll bet that once you get the hang of the careful and incremental adjustments necessary to properly set up your bass, as explained above, your bass will be quite stable and only require tweaking in the spring and fall.
(Message edited by s_wood on May 28, 2006)
