> The questions that have been proposed are intriguing, indeed: 1) does
> a small change in RH (e.g., +/-5%) at 30%RH produce a different rate
> of MC change than at 60%RH (i.e., how long does it take to come to an
> equilibrium), and 2) do these small changes happen equally in both
> directions, and at both levels? This would be interesting information
> to know concretely, in the case of the piano. Piano technicians
> should know this information, so these tests should be done. These
> tests don't require expensive equipment; it is a pretty straight
> forward data collection that piano technician should be able to
> handle.
Unfortunately, no. Not even close. This isn't a new thing. Concerning
tuning stability, a piano is a very complex system, the details of which
no two techs will agree on. Data in the form of tuning changes
accumulated by techs will be useless to answer these questions as has
been the case for as long as these questions have been asked. All of the
final effects we see in the tuning are the result of interactions among
a number of different reactions, none of which have been quantified in
isolation. Testing wood samples directly will answer the questions
directly without the obfuscatory complication of unqualified opinion.
This takes a modest lab setup capable of maintaining very close control
of temperature and humidity over long periods of time, and someone
capable of adhering to scientific method without guessing and editing as
they go to fit their personal preconceptions. It's not a group project.
It's a job for a real research lab.
We can't interpolate these wood reactions from periodic very poorly
detailed reports on the tuning, but if we can accurately quantify wood
reactions from answers to these basic questions we can better understand
what the heck it is we're seeing in those tuning changes, and the time
scales involved.
I know I'll catch hell for "poorly detailed tuning reports", but they
don't include nearly enough information to account for scaling effects
and what the climate did between measurements. This data is a snapshot
in time of a continually moving target that doesn't give us anything
like a point of departure for analysis. So for this purpose, it's useless.
We really need some real fundamental information on how wood reacts, and
at what rate, both absorbing and releasing moisture through different
ranges of temperature and humidity. Every wood study that has ever been
done has had this information go past right in front of them as they
went for other specific data. I find it incredible that it isn't
compiled somewhere in a usable format.
I've avoided it for years, but I'd just as well give it a shot. I'll
write to the Forest Products Lab in Wisconsin and see what comes of it.
I haven't thus far, because I fully expect to be asked for the name and
file number of the appropriate publication rather than to reach a
helpful person. I guess we'll see. Discussion among piano techs still
produces nothing, so I'll try this.
Ron N
Original Message------
I'm not sure what UK site that would, but I will be on the look-out for it--if I find anything, I will post my findings.
The questions that have been proposed are intriguing, indeed: 1) does a small change in RH (e.g., +/-5%) at 30%RH produce a different rate of MC change than at 60%RH (i.e., how long does it take to come to an equilibrium), and 2) do these small changes happen equally in both directions, and at both levels? This would be interesting information to know concretely, in the case of the piano. Piano technicians should know this information, so these tests should be done. These tests don't require expensive equipment; it is a pretty straight forward data collection that piano technician should be able to handle.
However, that information doesn't, necessarily, have a direct correlation with tuning instability. For example: when the piano is exposed to a prolonged and significant change in temperature, the plate will produce a change in the tuning that shows up in the 4 notes on either side of the strut; I have not observed this effect, at all, with moderate changes in temperature. Likewise, changes in the MC of the wood may also have a certain threshold before it begins to effect the tuning. <----the aforementioned tests won't directly show that kind of correlation.
I haven't tuned at 30%RH for a prolonged period of time--in an environment that I had enough control over--so I can't say for sure that it functions exactly the same. What I can say: at the 60%RH level, by tuning at the same temperature (i.e., tuning only after a scheduled events--so that the hall and piano was pre-warmed--then using the faders to set and adjust the specific temperature), none of the intermittent swings in RH manifested themselves in the stability of the tuning. We could maintain the entire tuning to well within 0.5 cents for weeks (i.e., most of the time, the strings were not moved more than c.0.2 cents).