[CAUT] Soundboard Heat Treatment? (LONG)

[Keith Roberts]

What's with what I heard about Strat's? That he soaked the wood in brine,
(no oxygen) then buried it in hot sand to bake out the water?

Keith Roberts


On 6/6/07, Scott E. Thile <scott.thile at murraystate.edu> wrote:
>
> Hello all,
>
> A friend is interested in some research he uncovered indicating the
> benefits
> of treating softwoods with heat or chemical means to increase sound
> transmission characteristics and stability. I think the thrust of the
> research focuses on using currently "inferior" woods in less expensive
> instruments, especially in light of shrinking supplies of top quality
> materials and an expanding demand to supply the Asian instrument makers.
>
> Some of this research seems to indicate treating already excellent
> materials
> could make them better still.
>
> Any of you designer/engineer/scientist types had any experience with this
> as
> it relates to pianos or done any research with it?
>
> My friend, John, relates the following:
> --------------
> "There is a bunch of literature on this, and the indications are that the
> treatment would improve several characteristics of the wood.  The best
> option seems to be heating the wood in the 200 deg C range for a period of
> 1/2 to 4 hours using a method that prevents oxygen from getting to the
> wood.
> (in the presence of oxygen the wood degrades pretty quickly when heated).
> one method is to heat the wood with steam, this removes the air and
> protects
> the wood from oxygen.  another is to do it in a pure nitrogen gas
> atmosphere
> or in a vacuum.  and there are other methods involving heating in an oil
> bath, etc.  the result is that it seems to do what aging naturally does
> over
> a period of decades, although the heat treatment only takes a few hours.
> among other things, the wood is 1) darker, 2) stiffer and more brittle, 3)
> has a higher modulus of elasticity, i.e. higher sound velocity and
> therefore
> better acoustic qualities, 4) better stability in response to changing
> humidity and less tendency to crack with changing humidity, 5) and best of
> all the moisture content is about 1/2 of that of untreated wood at any
> particular humidity level.  the one downside is that the wood is not as
> strong, i.e. it is stiffer and more brittle and will fracture at a lower
> bending force.  but this weakening of the wood is tolerable and is a
> function of the amount of heat treatment applied. seems like this might be
> great option for a piano soundboard and would lead to greater tuning
> stability, as long as the board was strong enuf to handle the downbearing
> force."
> ---------------
>
> Here's a link to a presentation from some research at the University of
> Dresden:
>
> http://campus.murraystate.edu/staff/scott.thile/07_59.pdf
>
> My initial reaction is that the best pianos I've heard are relatively new,
> or have relatively new soundboards, but older string instruments often
> have
> advantages over new ones. The difference no doubt has to do with the
> amount
> of tension, downbearing, and other forces at play. I think new, properly
> seasoned strong wood (weight to strength ratio) has a big advantage in
> pianos versus lower tension instruments. And conversely, lighter, older
> and
> more brittle wood has an advantage in lower tension instruments. So I
> would
> think the benefits of this extreme heat treatment would be more noticeable
> in lower tension instruments than it is in pianos.
>
> I just removed a perfectly good soundboard out of the Steinway 'O' I'm
> rebuilding this summer. I could not detect anything wrong with it at all.
> I
> just wanted to replace it with a new board because it has reacted to 40
> years of extreme humidity swings (it's not the original board--the piano
> is
> 65 years old). No cracks, good crown and me beating the thing out with a
> sledge hammer ;)). Even I had to cringe, but I'm convinced this is the
> best
> strategy here at MSU where we see 60% swings in humidity. Every rebuild
> gets
> a new board now!
>
> I LOVE the sound of the D I just finished rebuilding this January with a
> new
> Bolduc board--it's simply a fantastic board! No extreme heat
> treatment--just
> good wood that has been well constructed into a wonderful soundboard with
> more or less traditional techniques. Would it sound better if it had been
> extreme heat treated? Perhaps, but how would it age? Is the life span
> reduced as the tonality is increased with extreme heat treatment? My guess
> is it is. Perhaps like putting the thing in a time machine. Yes, it may
> sound better, but for how long? If the board needed to be "beefed up" in
> order to compensate for the reduced strength, does that negate the tonal
> effect? I bet it does....
>
> The most compelling thing mentioned in the research is that the treated
> wood
> takes on less moisture. Perhaps reducing the expansion and contraction due
> to humidity swings, which would help with the situation we have here at
> MSU
> (and many other locations), and that would add as much life as the loss of
> strength would reduce, and if it also contributed to better tonality and
> more stability, well that really would be interesting.
>
> Sorry this is so long, but I thought it was interesting.
>
> Any of you bright boys in back rooms have a take on this?
>
> Scott
>
> Scott E. Thile, RPT
> Piano/Instrument Technician
> ---------------------------
> Dept. of Music, Murray State University
> 504 Fine Arts Building, Murray, KY 42071
> Office Phone: 270-809-4396
> http://campus.murraystate.edu/staff/scott.thile/index.html
>
>
>
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