Originally Posted by BHBassman
I have my plywood basses in a dry room-notice that the string height does change acc. to the humidity/weather.
Also notice the resonance changes-sounded great last night & on a gig Sunday, but the G string buzzed last week. Raised the bridge & it helped eliminate the buzz.
Have used a Dampit in the past. Not sure of the effect.
Plywood basses do seem to change acc. to humidity level in & outdoors.
Spoke to a pro cellist that owns a $50,000 handmade cello that claims she does not have the issue,but think that plywood instruments seem to require repair- more sometimes than carved wood in her experience as a teacher.( student instruments...)
As for strings: EPs! Instantly improved the sound on my basses.
I've no idea why that 'cellist might have said that plywood requires more frequent repairs than carved wood. I've been repairing instruments of whatever size for over 20 years, and I see much more winter shrinkage-related cracking and seam failure even in violins than I see in plywood basses. Even the oldest Kay basses from the late 1930's are generally very stable in terms of extreme dryness. The worst problems I see in terms of plywood and humidity is when basses or ply 'cellos (not common around here, but there are a few Kay and Framus ply 'cellos) are left lying on basement floors for years at a time. I've seen a lot of rather severe de-lamination in those cases, and chasing down all the layers of veneer to adequately re-glue them is no small job, really takes a lot of sessions of careful gluing to get them into solid shape again. Wetness opens hide glue joints... duh. With most modern ply basses this isn't an issue since more stable synthetic glues have been used. The sound may degrade in lower humidity due to dimensional shrinkage and the resulting tightening of soundpost fit, and as stated previously the lowering of string heights (the belly arch is actually collapsing as it tries to get smaller when humidity leaves the wood), but this is much less likely to result in damage in a ply instrument.
Carved instruments are quite a different story. Of course they don't appreciate being left on a damp basement floor either, but most owners aren't as likely to leave such instruments in such conditions. So lower than healthy relative humidity is more often the cause of damage, displaying as splitting, especially in the spruce, and especially in the lower bouts where they're wider and the relative stresses are greater between ribs and belly. A tightly-fitted saddle is one of the worst culprits, as is a too-wide end block, both mistakes commonly made by instrument makers. A half-saddle, leaving the spruce intact for half the thickness of the lower edge, and fitting the ebony with a slight gap at each end almost eliminates shrinkage cracking there.
Seams will pop open if the humidity is too low and no preparation can prevent that, so using a humidifier is essential whenever humidity drops below about 35%. This applies to a lesser extent to laminated instruments, but I still see them opening due to dryness once in a while. It's still wood, and wood shrinks when it dries, across the grain not along the grain. Take almost any instrument of the violin family to Alberta in February where average un-corrected indoor humidity is often below 20%, and watch it crack somewhere within a week. I see a fair number of touring bassists. Before they're 30 they learn to fear the prairies in winter, as a tour's profits can erode quickly due to cracking. By their 30's they either rent local instruments, take their own plywood, or engage in various song and dance stuff involving motel shower steam and Dampits (up to 4 at a time).
I've seen a fair bit of damage to the lower ribs, lower back, and to the glued joints there because of Dampits. Mostly that's because there is almost no safe lower limit on water content with those things. You can wring out your Dampits (or other brand of the same thing) with a towel, swing them around for a while, wring them out again... but if there's gravity where you are, water still flows down to the bottom of the tube and can still drip out the bottom holes. If the sponge in the tube is so dried by these precautions that no dripping is possible, then so little evaporation is going to happen that any benefit to the instrument is lost. I've seen more than enough instruments with moisture stains in the lower bouts, making it abundantly clear that Dampits have been used.
What's the best solution? A cheap humidifier and a hygrometer to tell you when to use the humidifier. For $20 or less a very reliable digital hygrometer can be purchased. Make a habit of checking it at least once every day. When it drops to 35%, check it more often and consider filling a humidifier and turning it on. 45% is ideal, but 40% is sufficient for most instruments to be 'happy.' At 30% people start calling and emailing me, talking of cracks and open seems and wondering if maybe it's because it's so cold... Yes, dear bassists, the furnace (or baseboard heater, cube heater, steam system - at least those which don't vent frequently, even sub-floor heating systems) comes on when it gets cold outside. This heat drives away moisture unless there is a built-in compensation of some sort. The house gets dry, instruments crack, noses bleed, flus and colds are easier to acquire, plants need more frequent watering, etc.
Buy a $50 humidifier and use it, and save yourself hundreds to thousands of dollars in repair work and devaluation of your bass. Helps the sound too, when the post isn't being squeezed. I used a stock pot full of water on the stove or on a hot plate for years. Worked fine, if a bit hard to fine tune so the windows didn't drip with water. Then I used an impeller type Sunbeam humidifier for a few years. Worked great, but NOISY! Last week I bought an ultrasonic Sunbeam. Put that off for many years as the models I had heard were all painful to my ears, but I figured it was $50, worst case I'd have to give it to someone with less high frequency sensitivity. But either I've finally, at age 51, lost my high frequency hearing - YAY! - or this model (the SUL496-CN - a tall, tapering clear and white plastic tank atop a white base) is actually ultrasonic, as contrasted with the abundantly audible models I'd heard previously. Since I can still hear the school board's 'mosquito' teenager deterrent alarm when that's in use on the school next door, and it still gives me headaches, I think it's more likely Sunbeam got it right with this one. I have to fill the tank about every 36 hours when running it at 75% of maximum. It maintains my instrument room at 38% at that setting, so everyone's happy enough this winter, no new cracks are likely while basses and smaller fiddles reside at my place. At 100% it runs out of water every day and humidity goes to 45%, but that's overkill considering that it's better not to 'shock' instruments too greatly. Don't want to keep them too swollen here, only to have them go to places with sub-30% humidity and start cracking right away. A compromise.