Ok. On to Terry's last post.
First let me begin by saying this: The foundation of scientific research is Peer Review, it has been since the early days of the Royal Society. You can't simply announce "I've made a room-temperature semiconductor! Hurrah for me!" or "I've cloned a human embryo using nothing but common kitchen utensils!" You have to present more than a claim, and more than just results. Your peers then analyse your methods, and attempt to replicate your findings. If they can, then Peer Review substantiates your claims. If they can't, they'll investigate why they can't when you said you could.
Now to the substance.
Terry et al, leaving aside my (perfectly legitimate and still unanswered) objections (Terry's given us nothing but results and no methodology, see above) the latest argument presented is based on an entirely false premise. Let's consider this:
Terry McGee wrote:My measurements indicate that a 30% drop in humidity produces a shrinkage in a blackwood head of around 0.4mm (on the worst axis) and 0.2mm on the opposing axis. Of course it's the worst axis that concerns us, so let's take the 0.4mm figure. Now that's on the outside of the head, let's recalculate it for the inside of the head. Assuming there is going to be a liner, we can take that as 20mm. That would suggest 0.3mm shrinkage will occur in the wood at the outside of the liner.
BFMW's expansion figure for a silver liner was 0.00002 mm/mm/degree C. The liner is 20mm diameter, so that becomes 0.0004mm degree C for the liner diameter. 750 degree rise would produce a 0.3mm diameter increase.
What's effectively being said here is this:
"
All blackwood headjoints will shrink by 0.4mm and suffer catastrophic failure if they are subject to a 30% reduction in RH. A metal liner would need to be heated to ridiculous temperatures to effect the same catastrophic result, so we can forget the liner and temperature increases."
Can you not see that this is entirely wrong, even on a common-sense level? Those folks who keep their blackwood flutes encased in a tupperware box along with a wet sponge will subject their flutes to much greater than a 30% RH humidity swing the moment they take it out of the box on any number of days. Without ill effect, and without massive shrinkage of the flute occurring. That's a simple observation made every day by people all over the world.
A metal liner doesn't have to expand by 0.3mm to cause cracking. Let me give you an analogy using a commonplace model most people will be familiar with:
Remember the 'old' water sprinkler systems used as 'automatic' fire protection? They worked like this: A small, sealed, glass bulb filled with alcohol (coloured with a red dye) sat in the sprinkler head. The bulb held shut a spring-loaded valve.
If a fire broke out, the alcohol in the bulb would begin to expand as temperatures rose. The glass bulb would shatter, the spring-loaded valve would pop open, and water would spray out (hopefully extinguishing the fire).
Alcohol expands significantly as temperature rises. It has a low boiling-point. So how much did the alcohol expand before the glass bulb broke? It didn't expand at all. The glass bulb contained the liquid, preventing its expansion. Pressure built up on the surface area of the inside of the glass bulb, until finally the bulb burst.
What's this got to do with lined wooden headjoints? A flute isn't a glass bulb, certainly. But here's another everyday commonplace model to consider:
The plastic rule. You've probably done this yourself, I know I have. Consciously or otherwise sat flexing a plastic rule(r). Bending it back and forth. At first you can bend it quite a lot. But *some time* later, you're sat there flexing it and suddenly it shatters, loudly and violently. Loads of kids have been startled out of a classroom daydream by that kind of thing.
The wooden flute with a metal liner. Well, subjecting that liner to a sudden 30 deg F increase in temperature (which is a certainly a commonplace event in my home, centrally-heated to 68 deg F) will make the liner expand. Granted, not by much. But bear in mind that the alcohol in the glass bulb did not expand at all when heated, it was constrained by the glass tube walls. Thus, even a miniscule amount of thermal expansion can produce a significant pressure along the entire length of the liner through the headjoint and barrel.
How much pressure? I don't know. This is why I mentioned Young's Modulus, a measure of the 'stiffness' of a material (or indeed it's flexibility, if you like). In the case of the glass bulb, the 'stiffness' of the glass prevents it expanding. Pressure increases until it ruptures.
In the case of a wooden flute, pressure builds up, trying to burst open the headjoint and barrel. But wood isn't glass, it's elastic modulus is entirely different. Like the plastic rule, it can flex. A little. But like the plastic rule, is it such a stretch to conclude that after a certain (currently unknown) number of cycles of pressure and release, the wood will crack? That's what stress fractures are.
This is basic physics.
Of course, no two pieces of wood are the same. No two makers are the same, and no maker of anything can make two things which are absolutely identical. The flute that splits the first time it's played (irrespective of local humidity) may well do so because the wood contains a flaw, or because it's been stressed sufficiently throughout its life to take it to that critical point.
For what it's worth, the improved tuning slide that Terry uses, with its cork lapping expansion joint, is a great idea. If the liner expands when warm, the cork will compress, relieving the pressure experienced by the headjoint.
Terry McGee wrote:Now, having discounted temperature, we do have to remember that an increase in temperature will reduce the relative humidity in the air, and that drop in relative humidity is what might crack your flute. To clarify that apparent contradiction - a short term change in temperature is not a problem. A long term change (eg running the central heating for weeks in winter) will be, as it reduces the humidity of the air for that long period, long enough for the flute to dry out, shrink and crack.
Discounting temperature is wrong. a short change in temperature *is* a problem. It builds pressure, then relieves it. Stress-fracture in the making.
And the statement that raising the temperature of air reduces its RH is completely wrong too.
One Litre of air at 20 deg C can hold more water vapour than one Litre of air at 10 deg C. Which means if you place a wet sponge in a 1L container at 10 dec C and wait, the RH might rise to as high as 80% and stay there. If you turn up the central heating to 20 dec C, the relative humidity of that 1L of air in the box will *rise*, because the warmer air is able to hold more water vapour.
And the statement "a drop in relative humidity is what might crack your flute" is an opinion, which later becomes a definitive statement of fact: "A long term change (eg running the central heating for weeks in winter) will be, as it reduces the humidity of the air for that long period, long enough for the flute to dry out, shrink and crack."
Again, that's an opinion which hasn't been tested yet. I have a G flute in mopane with tuning slide and silver rings I haven't played for a long time (too long a time actually) which I looked at last night, in my flat which has had central heating running since last October and RH hovering around the 30-35% mark. It hasn't dried out, shrunk, or cracked. Making statements which sound definitive, based on a proven faulty premise, isn't right.
For what it's worth, I
have started controlled experiments myself. Phase one is complete, and I expect there'll be more as time progresses. Could take a week or two, so if the thread dies out please forgive me for popping it up again later when my tests are done.
Cathy and others are quite right; this is important to all of us who own wooden flutes. It's also important not to deter prospective players from taking up the wooden flute by making unsubstantiated claims.
Looking forward to continuing the discussion.
"It might be a bit better to tune to one of my fiddle's open strings, like A, rather than asking me for an F#." - Martin Milner
