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Here are some hypotheses about the physical nature of some effects observed with djembes exposed to heat, cold, humidity, dryness, desperate tuning and other physical factors :-)

Jairo Fonseca wrote in response to jerry z:

> My Friends,
>
> Do not forget the temperature, the heat makes everything bigger and bigger ... If >we place our drums near a bonfire it will tight up, the same happens if we put our >drums inside a closed car in a hot sunny day.
>
> So, be careful to tune the drum up when it is cold, if the temperature goes up the >drum probably will pop.

Temperature and humidity are two main factors that affect the skin's physical properties.

Humidity absorbed by the skin doesn't actually make it DILATE. It only makes it MORE STRETCHABLE. It means that less stretching force is required to achieve the same dilation. Theoretically it can have two opposite effects for us, depending on whether the skin is stuck to the bearing edge or can slide over it.

1. The skin is stuck to the bearing edge.

In this case, the pitch will go down. It's obvious by intuition to most people, but to some it's not, so I'll explain it just in case. Imagine two strings of the same weight and length, each stretched by the same force (for example, by same weights hung on
them). The only difference between them is that one is made from the cord you use to lace your djembe, and the other is made from gum. Which one would produce lower tone? The gum of course, because it is more dilatable. The same works with membranes as well. Dry membrane works like tuning cord, and humid membrane works like gum.

2. The skin is not stuck and can slide freely over the bearing edge.

A piece of reminder here - let's not forget one of Newton's principles (I forgot its ordinal number): The Mutuality Principle. Not only the tuning system stretches the skin, but also the skin stretches the tuning system. If we loosen the tuning system by taking off some diamonds, the skin will stretch the tuning system and shrink itself. OTOH, if we loosen the skin by exposing it to humidity, then the tuning system should stretch the skin and shrink itself too! That's why a drum's pitch can be humidity proof to some extent if these two conditions are satisfied:
1. The skin can freely slide over the bearing edge.
2. The tuning system is capable of shrinking when allowed by skin's looseness.

There is something to know about Remo(R)-like tuning systems:
they are absolutely incapable of shrinking. This is not a big problem with Remo(R) djembes though, for Fiberskyn (TM) is absolutely incapable of loosening when wet.

I also suppose that long straight sections of cord are the best accumulators of the dilation from which the tuning system can shrink. That's why djembes with very tightly pulled verticals, and with only one row of diamonds, tend to have stable pitch.

Jairo notices that "heat makes things bigger and bigger". It is thermal dilation. But then why our drums tighten up instead of loosening down when played next to a bonfire? Because they become dry. When you play towards a bonfire, the drum head absorbs thermal radiation and becomes much hotter than the air, so it
evaporates its humidity and shrinks. But thermal dilation still occurs and REDUCES the tuning-up effect! A simple experiment proves it: play towards a bonfire for a while until the drum sings very high, and then turn around and play on. You will hear the drum quickly tuning even higher up! It happens because the skin radiates it's heat out faster than it can absorb humidity back from the air. This effect has killed one of my heads. I left the drum in the sun for half an hour, then a cloud came and covered the sun, the skin rapidly cooled down and POP! I had to perform on a broken drum.

Regards,

DJ_Embe
Szczepan Holyszewski
rulatir@free.polbox.pl

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TUNING DJEMBE