Advice and questions on keeping your instruments in top form
#44459
So you may already know that if a skin gets dry, it gets tight, and if it dries out too much, when it's fully tuned up, it can pop. Like if you leave it in the car in the sun. Even a sunny window can do it. (I got a shell that way, from someone who stored their djembe in the front window and the skin bust)

What I didn't know, is that the opposite can also cause the skin to burst.

We had an extra rainy winter, and a small (10") Iroko Kambala djembe (from Cote D'Voire) which was tuned up high, popped. So that's weird right? Usually the skin gets slack when it gets moist. So the best explaiation I can come up with, is that the wood actually swelled with the extra moisture, and the shell/rim got thicker, and that expansion had more effect than the skin loosening from moisture. Also I did treat the skin with shea butter, so perhaps it was less affected by the humidity than usual, and stayed tight.

Also of note, the rim is a bit thicker than would be proportional for a drum of that diameter. Probably due to it being Iroko, and also the limits of hand-carving a thin rim. So effectively there is more wood to swell, per inch of diameter and skin. So I imagine this is less of a factor in a larger drum, or a thinner shell. Also oily wood, such as Lenke is probably more immune to this happening.

It may come down to the fact that it was tuned up too high, and I was unrealistic about how tight a small 10" djembe can get, but it held up fine for weeks or months until the heavy rain season.
#44494
I appreciate that Dr Tom, thanks, and I agree it seems unlikely to be the moisture. I was so confused.

What I know is that it was fine before the rain arrived, and then we had an inordinate amount of rain, (phenomena sometimes called "vertical rivers"), and that was when the skin popped, all on it's own, without being touched, and without heating or drying the house (we don't heat the house, just bedrooms).

I suppose it could have developed a small tear during or soon after tuning (it was tuned rather high at my request, probably too high). And then maybe the humidity made the skin softer, so it was able to grow and expand (It's about 7 or 8 inches long, running just above the flesh ring).

My theory was based on the fact that plant/wood fibers (made of cellulose) get wider/shorter when full of moisture and narrower/longer when dry. Same reason shells can split in dry weather. I doubt it could have swollen by much, but if the skin was at it's breaking point, it might be possible 'that was the straw that broke the camel's back'. It is a rather thin and soft skin, which is appropriate for a 10" head. So along with the high tuning, and the extreme (and sudden) amount of rain, it may have been an usual confluence of circumstances that did it in, which could explain why it's 'unheard of' for humidity to pop a skin, if it is in fact possible.
#44498
batadunbata wrote:
Mon Feb 10, 2020 3:47 am
My theory was based on the fact that plant/wood fibers (made of cellulose) get wider/shorter when full of moisture and narrower/longer when dry.
I actually did some quick research on how much wood can expand before responding, hoping an obvious proof or refutation would immediately emerge. Alas, though plenty of authoritative information is readily available, it would take more time than I'm ready to invest in order to formulate a convincing refutation (or confirmation) of your theory.

So I just trusted my intuition. What gnaws at me is my experience and understanding of how the world works, especially in relation to djembes, which does not jive with your theory.

It wouldn't surprise me if you were to take the time to plunge into all that readily available information so as to support your hypothesis. I'll keep an open mind.
#44505
Yeah in no way would i consider a skin breaking due to the wood expanding due to moisture. If there is that much moisture the skin would absorb it anyways and the skin is weaker when wet. Plus the drum does not absorb moisture perpendicular to the grain so simply doesn't make sense how the moisture would get in there. Like if you throw a few knots in the verts its gonna be way more increase of tension than a minimal diameter change in the shell! Still I reckon my theory of drum standing upright and popping the skin is the most plausible reason for this scenario! Of course I'm right! :ubergeek: Its all about the coefficient of thermal expansion m'kay...
#44512
I suspect you're right Dr Tom, that it wouldn't expand that much from moisture in the air, though I know Guitars do improve their sound rather rapidly when the air is moderately humid, vs when it's too dry. So I can imagine thicker wood taking longer, but having a similar ability to rehydrate to some extent.

Hey The Kid, well it was stored upright, I'm not sure how that would affect it? From my experience with wood, it always swells perpendicular to the grain when humid. As far as I understand, the water goes in through the pores , which are openings to the capillaries that run vertically, and it gets wicked along the capillaries (how trees transport water up from roots). Then the cellulose absorbs it from the capillaries, and the wood swells sideways, not vertically, because cellulose fiber expands laterally when moist.


I've seen the base of a ukulele neck expand so much that it made the top and back bulge. But that was from overdoing humidification through the soundhole, not absorbing it from the air. It shrank back down after a while at lower humidity.
#44513
I simply found drums pop easier when standing up. I though more about it before and may have had theories but nothing too concrete. It was doubted by some yet it keeps coming up that a skin pops while standing up after change in weather or whatever. I was thinking it can be due to temperature\air pressure inside shell being different to outside the shell. Like the air inside is trapped and then then the atmosphere changes and the skin is in some internal flux or tension due to say hot high pressure inside and cold low pressure outside.
#44533
Ah, that is an interesting thought.

Well of course they tend to be standing up, but presumably the Kid has experience with ones stored on their side, which is more space efficient since they can be stacked, or placed on a high shelf. But I had the same thought, having never done that myself, like 'of course it was standing up, it's a djembe!'.

As for the difference inside the drum when standing to the air outside, that actually makes some sense.
Not so much the air pressure, as I think even a tiny air gap around the foot would allow the interior to adjust, not to mention that air pressure is much less than a drumstrike. But the moisture and cool temperature would be significantly sheltered inside for longer on a hot day than the outside. Less air flow means less heat exchange and drying.

There is a parallel in guitar luthery, when making the top of the guitar. One luthier on the classical guitar forum observed that in the morning, the top, sitting on a table surface, would be flat. Then, as the day heated up, and the air dried, the top would eventually start to curl upwards. His thought was that the side faced down was protected from drying out as much, as it had less air flow, and the exposed side dried with the heat and lower humidity. He noticed it would be flat again the next morning, and the whole process would happen over again. Day after day.

I imagine the interior air of a djembe would be similarly different from the outside, though the skin might be a bit more breathable than wood, since it's so thin, it's still a whole lot less airflow. So on a hot day, it would be cooler and moister inside, and outside would be drying. So there would be a tighter side and a looser side of the skin, essentially. Which could cause internal forces in the material, and perhaps shearing, especially in areas under the most strain? It's an interesting thought. A drumhat would probably be helpful in such a situation. Even a showercap or something.
In my case, the inside would have been dryer, and the outside would have been moister, but it is still a difference between the two. I wonder if that's what did it. It does seem more likely than the rim of a djembe swelling by a significant amount.
#44535
batadunbata wrote: As for the difference inside the drum when standing to the air outside, that actually makes some sense.
Not so much the air pressure, as I think even a tiny air gap around the foot would allow the interior to adjust, not to mention that air pressure is much less than a drumstrike. But the moisture and cool temperature would be significantly sheltered inside for longer on a hot day than the outside. Less air flow means less heat exchange and drying.
That's seems like good reasoning. The interior is probably insulated to at least some extent and perhaps to a significant extent.

Still not convinced this is responsible for the skin popping.
batadunbata wrote:There is a parallel in guitar luthery, when making the top of the guitar. One luthier on the classical guitar forum observed that in the morning, the top, sitting on a table surface, would be flat. Then, as the day heated up, and the air dried, the top would eventually start to curl upwards. His thought was that the side faced down was protected from drying out as much, as it had less air flow, and the exposed side dried with the heat and lower humidity.
What a great observation by the luthier! The top of the top (exposed to the drying air) looses moisture, while the bottom of the top (not exposed to the drying air) does not. So the top of the top shrinks but the bottom of the top does not, resulting in the top curling topwards.

Off the top my head, though, still don't see this popping that top.

batadunbata wrote:I imagine the interior air of a djembe would be similarly different from the outside, though the skin might be a bit more breathable than wood, since it's so thin, it's still a whole lot less airflow. So on a hot day, it would be cooler and moister inside, and outside would be drying. So there would be a tighter side and a looser side of the skin, essentially. Which could cause internal forces in the material, and perhaps shearing, especially in areas under the most strain? It's an interesting thought. A drumhat would probably be helpful in such a situation. Even a showercap or something.
In my case, the inside would have been dryer, and the outside would have been moister, but it is still a difference between the two. I wonder if that's what did it. It does seem more likely than the rim of a djembe swelling by a significant amount.
Well thank you for that BDB. Now I'm going to be fretting over which side of my skins is tighter!

batadunbata wrote:Which could cause internal forces in the material, and perhaps shearing, especially in areas under the most strain? It's an interesting thought.
R e a c h i n g ?
batadunbata wrote:In my case, the inside would have been dryer, and the outside would have been moister, but it is still a difference between the two.
That's true and a keen observation.
batadunbata wrote:I wonder if that's what did it.
We may never know.

What we do know is that all drumheads must be replaced periodically. It's their nature.

This is especially true for djembes. Given the incredible force required to get djembes tuned, it's amazing that they hold out as long as they do. Standing, sitting, squatting or laying down.
#44536
Reaching for sure. I just don't like not understanding, so I seek to find the answer.

But your point about skins needing replacing, and how they hold up surprisingly well considering the tension and beating they take is spot on. When I learned the amount of tension on a drumhead (as I recall it was Michi who said it can be in the range of 500-800Kg - but maybe that's once I converted it into pounds, I can't remember) I was astonished that such a thin material could take that. The fact that it can warp a shell out of shape (egging due to the the spine line) means it's some tough stuff.

This was a particularly supple fibrous skin, so it probably wasn't as strong as one that feels more dense and stiff.

But that still doesn't explain why it popped when it rained a whole bunch. It wasn't being played much, it had sat basically unused for months. Oh well, it's a mystery, I'll have to live with that.