Could EMC be an answer for a tuning problem?

Bo Legg · Posted 21 Jan 2010 6:44 pm

EMC equilibrium moisture content

The temperature affects the tuning of the PSG due to the expansion of the wood as it is affected by the heat.

Because of its hygroscopicity, wood tends also to shrink and expand depending on the moisture content.

The outer surfaces of the PSG cabinet are sealed with some sort of paint which decreases the moisture change.
The underside of the cabinet is also painted on most PSG and this decreases the moisture change.

Unsealed wood will loose moisture and shrink when heat is applied.

Why not leave the underside of the cabinet unpainted so that the cabinet could take on or give off moisture as the temperature changes?

As the temperature rises the wood expands, the moisture content decreases and the wood shrinks, offsetting the effect of the temperature change and therefore less affect on the tuning.

Kevin Hatton · From: Buffalo, N.Y.

Hardly a factor.

Bo Legg · Posted 22 Jan 2010 2:02 am

Kevin, I assume when you say "Hardly a factor" you mean something more than "Not a factor".
We're dealing with very small numbers of cents in tuning affected by an even smaller number in percentage of expansion here.
What would be the benchmark for “Hardly a factor” in cents?
I would think results of as little as 4 cents in tuning would be noticeable.

Georg Sørtun · From: Mandal, Agder, Norway

4 cents in overall detuning is more than enough to notice.

I think you'll have problems getting a stable canceling effect in something as non-uniform as wood, any wood, though.

1: The wood will take up heat at a much faster rate than it will let off moisture, so it'll expand quickly and shrink slowly, thus skewing the effects.

2: Moisture gets drawn out of wood under cold air conditions too - depending on actual moisture-content in the air (think about freeze-drying as an extreme example), so the "balancing act" will be highly unpredictable.

I think the wood should be left well sealed, or materials that are more predictable than wood in this respect should be used.

J D Sauser · From: Wellington, Florida

Moisture and temperature fluctuation mostly the wood fiber's size (width) and only to a much, much lesser extent (hardly noticeable) the length.
So, hardly a factor when causing tuning caused instability by "length variations" of the guitar.
It may affect a poorly designed guitar where the variations in width have not been taken in account at the time of development: Vital parts like the key head and the changer may become unstably positioned or even loose. I would not know of a modern day PSG where that would be the case however.

... J-D.

Kevin Hatton · From: Buffalo, N.Y.

Metal expansion and contraction is more of a factor. Also, as JD said, loose parts, and a poorly designed guitars. Playing in direct blazing sunlight on your strings will have a much bigger effect. You can throw an Emmons push pull down in 35-40 degree weather and the tuning won't move. I've done it.

Chris Johnson · From: USA

......... Then there was that one time I saw a Push Pull Emmons flying outside my plane window Laughing

Just for laughs

chris ivey · From: california (deceased)

hygroscopicity is one of the main reasons i don't tune precisely. then my imprecise playing combines with this, and hysteresis , cabinet drop and not keeping my bar perfectly parallel when moving up or down while the air conditioning in the club goes on and off, not to mention the drums, bass and noodling guitar which drown me out totally, to present a perfect blend of precise harmonic beauty.

edited to correct splelnig

Bo Legg · Posted 23 Jan 2010 8:04 am

After reading all the very informative replies here, I can see that my lack of knowledge regarding this subject caused me to come to an unpractical conclusion.
However this bring me to another question regarding moisture and wood.
http://bb.steelguitarforum.com/viewtopic.php?t=176075

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