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Aged Tone wood stability, tone.

Posted: Sat Mar 14, 2020 8:59 pm
by Daniel Oates
Aged tone-wood appears to be highly desirable in instrument building. How much of this is for the development of the tone and how much for the stability?

Re: Aged Tone wood stability, tone.

Posted: Sun Mar 15, 2020 11:26 am
by Alan Carruth
More for stability than tone,I expect.

As it ages and undergoes moisture cycling the hemicellulose in wood breaks down. This is a sort of 'filler' in the lignin 'glue' that holds everything together, and it's the part of the wood that actually absorbs moisture from the air. As it goes away the wood can't hold as much moisture, so it shrinks a bit ('shrinkage hysteresis') and become more stable. The loss is slow, but it's probably the main difference between new wood that is simply 'dry' and older 'seasoned' wood.

As the hemicellulose breaks down the wood becomes a bit less dense, and also loses a little stiffness, but the density drops off faster, so the stiffness to density ratio goes up. That should make the instruments louder all else equal, but we're talking really small percentages here: on the order of 1%.decade.

It also seems as though the bond between cells is a bit weaker; it's more prone to splitting. That's not too surprising, since there's now air where there used to be hemicellulose. Old spruce becomes progressively more opaque due to the air spaces, sort of the way a snow bank made of transparent ice won't let light through.

If instruments do 'warm up' or 'play in' (which is plausible but not established) it could well be that older wood would do so more quickly. Since we don't know whether this happens, or what the mechanism might be if it does (lots of guesses but no proof so far) that's just conjecture.

I have made instruments using old wood: on the order of 100-150 years and some a bit more. They sound 'new' when they're finished; there doesn't seem to be any difference attributable to age once you've taken the stiffness and density into account. Again, there is a bit more of a tendency for things to split along the grain,so you have to be careful carving.

Re: Aged Tone wood stability, tone.

Posted: Sun Mar 15, 2020 10:13 pm
by Daniel Oates
Thanks Alan, that’s a good explanation.

Re: Aged Tone wood stability, tone.

Posted: Mon Mar 16, 2020 11:30 am
by Clay Schaeffer
I would agree with Alan that the principal advantage of building with well aged tonewood is stability. Another advantage is that the stiffness and density are less apt to change much over time.
Most of the soundboards I use are at least 10 years old and have spent much of that time in an environmentally "open" attic, undergoing seasonal changes of temperature and humidity.
Some people have been drying out their soundboards in a 200 degree (F) oven to "Preshrink" them and make them less reactive to humidity changes. I have done that and it doesn't seem to hurt and may help.
And then there is Torrefaction - wood "seasoning on steroids". And as with steroids, there are some gains and losses with it's use, and the long term effects are unknown.
My advice would be to buy a couple dozen soundboards, sticker them, and put them some place where they will under go the seasonal changes but be out of the elements. Until they are a few years old, heat treating them in an oven before use may not be a bad idea. If you buy "A" or "AA"grade stock you may get a dozen sets for the price of one "Mastergrade" soundboard. And although they won't match it cosmetically, the physical properties are often as good (sometimes better) than the higher priced stock. I build a number of smaller instruments and can often cut around the cosmetic defects and "upgrade" the cosmetics.