Hey,
I've got a couple questions, just out of curiousity, for those who know about the construction of acoustic guitars. I'm getting an older acoustic shipped to me and have been reading up on care/maintenance and a few things have jumped out at me:
1) Humidity - what's so magical about this 45%-55% relative humidity range? Does the wood actually sound better or does it just happen to be an average number? I live in Alberta, Canada and the RH is probably mid 20's this time of year, and only getting worse as winter progresses. I understand that if the wood on a guitar dries out it shrinks and can crack, but why doesn't any manufacturer season the wood to low values such as 20% RH before they build the guitar. Then in places where it's dry they wouldn't need to worry about shrinkage or cracking - the wood would essentially be 'pre-shrunk'. Is there any technical reason they don't or would it just be too much work to build some for 'dry' places and some for 'humid' places?
2) Finishes - As a woodworker, finishes have 2 purposes - looks and to protect the piece, but the more I read about guitar finishes the more fragile they seem. Lacquer can check & crack if exposed to different temps, it seems to react with almost everything from leather guitar straps to foam padding on a guitar stand, etc..., it can get cloudy with age and the list seems to go on and on. I've also heard that the finish needs to be very thin so it doesn't ruin the sound. Then I saw some guitars advertised with 'satin' finishes or 'semi gloss' that they claim allows the wood to 'breathe' more and therefore sound better. So my question is if lacquer finishes are seemingly more fragile than the wood itself, and all they do is impede the sound quality what's the point of them anyway? Why not just build a guitar with no finish? Is all this trouble just for looks? Usually the finish is just clear anyway, so why not leave the wood alone.
Anyway, these were just a couple things that popped in my mind, so if anyone knows some answers I'd really like to hear them.
Thanks,
the unfinished wood inside an acoustic guitar will continue to be susceptible to humidity changes regardless
http://www.maurysmusic.com/humidity___acoustic_guitars
"How does relative humidity affect guitars?
Wood will try to equalize to it's surrounding air, in temperature and humidity. If wood becomes too moist it will swell; on the other hand, if wood gives up it's moisture, it will shrink. All are physical characteristics of wood."
#4491....
cracks in the finish occur through gentle time. but cracks also appear prematurely in finishes from extremes in humidity and temperature. a friends three year old tele has hundreds of fine surface cracks due to his gigging then a long cold drive home; often leaving the instrument in the trunk overnite. my guitar, of the same age, has no cracks. it does not have the regime as his.
tone is affected by moisture levels in the wood too. our ears probably cannot sense it.
above fifty percent humidity and a warm temps (70's and up) mold can form.
gentle temp and humidity swings are the ticket to longevity.
I also think that the wood structure itself has more to do with tone than a finish.
of course, a thick finish will hamper tone.
Finish on an acoustic guitar is just there to make it look prettier. The effect of finishes on tone has been greatly overstated IMO. Shellac is the original stuff. Nitrocellulose lacquer is a cheap synthetic substitute for shellac that's come to be regarded as a premium finish because a lot of guitars that used it have become classics with passing time. Both are good finishes because they're easy to apply and easy to touch up, not because they're resistant to wear and damage. Polyurethane's about as durable as it comes, but try to refinish a spot. As for "breatheable" finishes, the wood's quite thin and it's bare on the inside surface, so the wood "breathes" in every case. Not to mention that "satin" finishes are normally just lacquer or varnish with ground quartz in it to dull the shine, not any more permeable than shiny varnishes.
If you built guitars in a dry environment and then they went to a humid one, the wood swelling would cause the top to bulge, the action to rise, and the sound would become dull. That's what happens already with the ones that are built in ~50% humidity. And if one's way overhumidified now, as when a humidifier's left in the case year round, the swelling wood will crack and shed the finish and the top, back and ribs are likely to separate. Drying the wood further would only increase the problems with that sort of thing. The builders have hit on a happy medium that works well enough in most situations. They've thought about this a lot, and had a lot of experience with the results.
"A cheerful heart is good medicine."
