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Old 12-23-2012, 03:39 PM
Von Beerhofen Von Beerhofen is offline
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Default Different absorption levels for different woods?

I've been wondering wether some types of woods absorb more moisture then others. I guess this must be true due to differences in intermolecular spacing, i.e. softer/lighter woods absorb more and quicker then heavier/denser woods. I've come with this topic as I can not really determine wether my Koa top is curving because of string tension on the bridge or moisture. As far as I can tell the guitar had this curvature during the summer too, but I can't say if it had been properly humidified in the shop, which is advertised as an authorised dealer.
Some websites state that a bit of curvature from the bridge to the edges is normal and some guitars are even designed specifically to use this.
Is this true for Taylor Koa GA's too? The guitar has a gloss coating which should slightly influence moisture absorption positively, as opposed to satin finnishes. However my friend (a violin repair guy), states that curvature can also occur due to temperature changes to gloss finnishes as the wood expands differently then today's synthetic finnishes, which are very hard and durable.

Ludwig
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Old 12-23-2012, 03:55 PM
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patticake patticake is offline
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i've read widely that cedar is less sensitive to moisture, and i believe the same may be true of koa as when i've played koa guitars in very humid stores, they seem less affected.

there's no reason to believe that a gloss finished guitar would be less affected by humidity than a satin finish, and since the inside of the wood of most guitars is unfinished, that side is wide open to the humidity in the place the guitar is stored/played.
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Old 12-23-2012, 04:07 PM
Ed422 Ed422 is offline
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Different woods have different absorption rates. There are tables produced by lumber companies and trade groups which give baselines for various woods.

As stated, most acoustic guitars (like 99.5%) have no finish inside.

Satin finishes are as waterproof as gloss.

The wood bending because the finish is too strong sounds whacky to me.

I think some amount of curvature to a guitar top is normal.

Ed
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Old 12-23-2012, 06:59 PM
clintj clintj is offline
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While there is some minor difference in water absorption rates, by far the bigger difference is the rate at which different woods expand for given changes in moisture content. Wood reacts to rising moisture by growing tangential to the growth rings. IOW, as wood dries, the rings attempt to get shorter. If you look at a log in the woodpile, this is why there are splits in the ends. Lesser growth is seen from inside to out perpendicular to the rings. This is why quartersawn lumber is prized for furniture making. It changes shape less with moisture than flatsawn and is more stable. Virtually no growth is seen lengthwise, relatively speaking. Applied to a guitar top, the main X braces run across the top and do not get longer as RH rises. The soundboard will try to get wider as moisture rises, but is locked in place by the bracing. Since it can't go out, it must go up, creating or accentuating an arch across the top. At the other extreme, as the soundboard dries out and attempts to get narrower, the braces lock it in place until enough stress builds up to crack the top which relieves the tension.
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Old 12-23-2012, 10:48 PM
Von Beerhofen Von Beerhofen is offline
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Thx for the answers guys, apreciate it. However this leads to the next question, Taylor documentation shows the differences in dry and moist situations and draws the top absolutely flat in optimal conditions.
This guitar has had this curve right from the moment I bought it from the shop. Although not really pronounced it's clearly visible when the top reflects light and worse on the bass side. Is this normal for a GA?

Ludwig
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Old 12-24-2012, 12:10 AM
Catan Catan is offline
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Actually, Taylor shows you that a slight convex curve is normal; it's the bulge that means that there is too much humidity and dip that means too dry (by far the worse of the two scenarios)

http://www.youtube.com/watch?v=43sbE9n7zv4
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Old 12-24-2012, 01:15 AM
Von Beerhofen Von Beerhofen is offline
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Right on! I came across that series of videos after searching numerous pages in Google. In my opinion the Taylor vids were the best answer I found. Worst were all the other repair shops where one even stated that inspite of the string tension the top should remain flat (perhaps that's true for another brand though). Another one talked about strings hitting the fingerboard when too humid and high action when too dry, where in effect it's exactly the other way round, slip of the pen I guess.
Took me quite a while to take all my worries away, Thx Bob!
The guitar is still perfect, inspite of not being in a case in an unheated room, midwinter, at average temperatures of app. 15 Celsius and a lot of wetness outside. I'll keep monitoring it's behaviour and perhaps buy a hairdrier, which I think is a better investment in such a wet country as mine then a humidifier. It's even worse in the UK now, so beware over there! Thx for the input.

Ludwig
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Old 12-24-2012, 07:14 AM
Ed422 Ed422 is offline
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On the Taylor site there are Tech Sheets. They give a great overview of just about all things guitar.. from too dry to too wet... from truss rod adjust to tuner maintenance... from neck angle to saddle height... A worthwhile read IMO.

The is also www.frets.com . A great set of articles on everything guitar.

Ed
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Old 12-24-2012, 12:14 PM
Von Beerhofen Von Beerhofen is offline
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Thx Ed,

yes, I've been there and read everything. Great info there!

Ludwig
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Old 12-24-2012, 12:48 PM
DanPanther DanPanther is offline
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Seems to me the harder the wood, less likely to absorb moisture, in the exception of Cedar, I would guess the high oil content of the wood would account for that. Just a thought.
Dan
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Old 12-30-2012, 07:30 PM
Von Beerhofen Von Beerhofen is offline
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After more research on the web I found this:

http://www.esf.edu/scme/wus/document...mberFPL531.pdf

which might be of interest to some.

Additionally I found that it's commonly accepted that:
hardwoods are less influenced by moisture.
Quartersawn wood is less influenced then flat sawn.
Heartwood seems to be even less influenced.
Moisture intake is higher when it's warmer.
All woods have different saturation points.

Instrument care instructions from the Collings website:

http://www.collingsguitars.com/care.html

Ofcourse this doesn't cover all of it, you can find much more information on specific species of wood by searching the web for 'wood hygroscopicity'.

Ludwig
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Old 12-30-2012, 07:41 PM
Ed422 Ed422 is offline
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Quote:
Originally Posted by Von Beerhofen View Post
After more research on the web I found this:

http://www.esf.edu/scme/wus/document...mberFPL531.pdf

which might be of interest to some.

Ludwig
Nice! I only did a scan, but it only looked like domestic (North American) woods.

Ed
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