Why are so many shells oval, not round?

[atam]

Does anybody know, why are so many shells made quite far from round (I mean when watching a drum from the top)? Is it for the wood structure of particular logs? Or just imperfection of the manufacturers? (I seen many of them measuring the shells during production..) Or other reasons?

[michi]

Most shells are carved when the wood is still green and hasn't fully dried out. Two reasons for that:

• It's an awful lot easier to carve when the wood has some residual moisture in it because it is much softer then.
• It is difficult to find a log that is fully dried out but doesn't have a split. Often, when you let a solid log dry, you end up with radial splits through the log (from the perimeter towards the centre) because the wood contracts at different rates depending on the distance from the heart.

Because the wood is still green when the shell is carved, the shell can end up out of round even if it was perfectly round to start with because the wood may not contract evenly as it dries.

The skill of the carver has something to do with it too. Carving a perfectly round shell isn't that easy and, depending on how much care is taken, the shell may be slightly out of round to begin with.

Cheers,

Michi.

[e2c]

AFAIK, this (round or out of round) is also dependent on:

- the fact that "perfectly round" isn't how tree trunks tend to grow (in general)

- taking care to allow a new shell sufficient time to cure before heading it for the 1st time (should save many shells from going out of round)

of course, I don't build drums, so there's probably stuff that's not occurring to me - beyond michi's list of reasons, that is.

[atam]

Because the wood is still green when the shell is carved, the shell can end up out of round even if it was perfectly round to start with because the wood may not contract evenly as it dries.

Thanx for this explanation Michi - it sounds very reasonably - and never come to my mind alone ! I was all the time meditating on what influence it can have on the sound...(whether they don´t do this oval shape intentionally..) and why even some expensive shells from flawless wood are just quite oval.

In general, I like round shells much more, but it is only for my perfectionistic taste. In general I did not find many sound advantages of the perfectly round ones. But I just hate to see, when someone puts the skin with the backbone mark on the shell regardless of its oval shape - I just like symmetry here and hate to have different angles under left and right hand. This can optically make the drum even much more asymmetric than it really is. But many people just dont care obviously.

[e2c]

I have seen a good shell - really good one - go out of round because it was headed a bit too soon. (Wasn't dried enough, or "cured," as michi mentioned above.) The rope, rings and skin exert tremendous pressure on the shell, and if the wood is not sufficiently dry when the shell is headed, it can - and will - warp.

My sangban is just a tad oval, but that's entirely due to the shape of the log it came from.

[atam]

The rope, rings and skin exert tremendous pressure on the shell, and if the wood is not sufficiently dry when the shell is headed, it can - and will - warp.

This also sounds reasonable, and I find it interesting that the wood can be so "flexible" in shape without finally breaking..

None of the shells I headed ever did this, but probably none of them was so fresh..

[michi]

I was all the time meditating on what influence it can have on the sound...(whether they don´t do this oval shape intentionally..) and why even some expensive shells from flawless wood are just quite oval.

The slightly oval shape doesn't seem to have a negative impact on sound, provided it is headed correctly. Many brilliantly sounding djembes are not perfectly round.

But I just hate to see, when someone puts the skin with the backbone mark on the shell regardless of its oval shape - I just like symmetry here and hate to have different angles under left and right hand. This can optically make the drum even much more asymmetric than it really is. But many people just dont care obviously.

Symmetry is important because, if the spine isn't symmetric with respect to the shell, you can end up with different pitches left and right of the spine (which is where people normally play).

When I skin up a new shell, I spend quite some time figuring out where the spine should go. I try to make the areas left and right of the spine as symmetric as possible, so the drum sounds the same left and right. Personally, I prefer to put the widest part of the drum in the east-west direction, because that maximizes the amount of room that is available to place the hands. But some people prefer to put the widest part in the north-south direction. The argument for this is that there is more tension along the spine than across it, which helps to minimize the amount by which the shell goes out of round.

I've never seen a goat skin tight enough to actually change the shape of a shell, so I'm not sure that the latter argument is correct; either way of skinning the drum is fine--it's a matter of personal preference and sense of aesthetics. But symmetry isn't just a matter of aesthetics: it does affect the sound.

Cheers,

Michi.

[atam]

But symmetry isn't just a matter of aesthetics: it does affect the sound.

Yes, it definitely does - and I forgot about this most important aspect in my respective post. In general, I dont mind any esthetic flaw too much, if it sounds excellent. But if it does not, then I mind everything !

[e2c]

I've never seen a goat skin tight enough to actually change the shape of a shell, so I'm not sure that the latter argument is correct; either way of skinning the drum is fine--it's a matter of personal preference and sense of aesthetics. But symmetry isn't just a matter of aesthetics: it does affect the sound.

per the friend who headed that particular drum (who is a professional drum-builder and has built a number of drums for me), the shell went oval because he didn't wait long enough for it to cure before heading it. Ever since that happened, he's been letting shells cure for a much longer time and hasn't had any further problems, AFAIK. And with that particular drum, it took some time before it started going out of round. (At least a month; I almost bought it - he later sold it at a considerable discount due to the fact that it had gone oval, but either way, it's a very nice drum.)

Remember, it's not just the skin that's exerting pressure on the shell - it's the rings and ropes!

I think you've been very lucky to never have had this happen to any of your newer shells, really. I also have to wonder if this is, to some degree, climate-related?

[michi]

per the friend who headed that particular drum (who is a professional drum-builder and has built a number of drums for me), the shell went oval because he didn't wait long enough for it to cure before heading it. Ever since that happened, he's been letting shells cure for a much longer time and hasn't had any further problems, AFAIK.

OK, I can see how this can happen if the wood isn't fully cured yet. In that case, I'd expect the narrow side of the oval to end up where the spine meets the bearing edge.

Remember, it's not just the skin that's exerting pressure on the shell - it's the rings and ropes!

I don't think it could be the rings and ropes because they all pull equally and in the same direction (at least for a properly built drum).

I think you've been very lucky to never have had this happen to any of your newer shells, really. I also have to wonder if this is, to some degree, climate-related?

By the time the shells get to me, they've had months in Africa, a few weeks at sea, and a few more months being in a warehouse somewhere, so they are well and truly dry when I fit the first skin. I don't know whether climate is related, but I can see it happen: in a humid climate, the shell would lose moisture more slowly and so take longer to cure.

Cheers,

Michi.

[e2c]

michi - i believe I mentioned the wood not being fully cured a few posts up?

as for any further thoughts on the matter from my friend, I'd have to ask him...

Re. the shells you get having ample time to cure: i bet that explains it!

[shortypalmer]

I have found that shells become oval due to pulling tension of the goatskin or cowhide, if you notice that when you see an oval shell it is usually shorter on the spine, the spine pulls tighter then the sides of the goat. not all shells do it, not sure why, my guess is a combination of skin and shell. a thinner carved shell would have a better chance of going out of round. the trick is when you rehead the drum, put the spine down the long side of the oval, it will actually correct it some, as a side note, every oval drum i have played sounded real good.
shorty

[thrinley]

i have a shell which i play for a year and it is round, when i rehead, pulling too tight on spine, the djembe eventually becoming oval. do you think it can be save? when the next time i rehead it?

[shortypalmer]

In my opinion you really have not lost much. the drum still sounds good i bet, when you do rehead just put the spine on the long side
shorty
www.goatskin.com