Porting a Dundun?

[Dugafola]

do your duns have a little hole in the middle?

[michi]

do your duns have a little hole in the middle?

Mine? No, they are closed.

After the experiment we did showed virtually no change in sound with and without the hole, I decided that I'd prefer not to drill a hole into my beautiful dunduns, despite a mate preaching to me until he was blue in the face that my dunduns will sound "much, much better" if I add a hole

Cheers,

Michi.

[Dugafola]

i'm not convinced they improve sound at all either. but they may help in making your skins last longer.

[michi]

i'm not convinced they improve sound at all either. but they may help in making your skins last longer.

Maybe. I'm not that confident about extending skin life significantly that way. In my experience, skins break because they wear out (get thinner over time) in the center from being hit repeatedly. I've also seen them wear out at the bearing edge on dunduns that are played ballet style, when people strike the edge as if it were a bell.

The hole no doubt does have some effect on the sound. Imagine starting with a teeny-weeny hole the size of a pin-prick. Obviously no noticeable change in sound that way. Now progressively make the hole larger until it is something really extreme, say, six inches in diameter. At some point, the hole will effect the sound noticeably. (Make the hole large enough, and there is hardly any dundun left )

It's just that a hole around half an inch to an inch in diameter doesn't make a lot of difference. That's no surprise when you consider the wavelength of the sound waves of a dundun. On a dundunba, wavelength is several meters which totally swamps the the size of the hole…

Michi.

[Trumpet]

Thinking about this some more, I know that my dunduns go up in pitch quite noticeably on a hot day.

But that's not caused by increased pressure inside the drums or by a change in the speed of sound. Rather, as the shell and rings warm up, they expand, so they have a larger diameter. At the same time, the increase in temperature drives moisture out of the skin, causing it to shrink.

The two effects combine to increase the tension of the skin, so the skin's resonant frequency goes up.

Cheers,

Michi.

Funny you should mention that. This morning we had a concert and it was easily the hottest day we've had all year (91 degrees), yet this was the lowest the Dun sounded. Go figure.

[michi]

Funny you should mention that. This morning we had a concert and it was easily the hottest day we've had all year (91 degrees), yet this was the lowest the Dun sounded. Go figure.

Wow! That really surprises me. I have no idea why this would happen…

Hmmm… As it gets hot, the rope expands too, so it gets longer. In my experience, that doesn't seem to compensate for the rise in pitch due to the larger diameter (and length) of the shell, and the shrinkage of the skin. But, just theoretically, if you happen to have a type of rope that expands more than usual with temperature, that could explain the drop in pitch.

To be honest, I'm just guessing here though…

Cheers,

Michi.

[Rhythm House Drums]

Can't stay away from this forum for too long.. Here is my experience with the holes.

I ported my ballet style dunun that this 32" tall. It is always sitting with one head on the ground when I play. I've got (2) 2" holes ported about 1/3 of the way up. I figured the length of the tubes by using some speaker sub woofer program to approximate the frequency I wanted to hear. With one head on the ground and not vibrating, there is little difference when I cover the sound holes, the harder I play the top, the more I can hear a difference, though the biggest difference I hear is still subtle. My theory in the holes was that the distance between the heads was so long, that they might not vibrate uniformly and make funny overtones. I also was thinking this would help release the pressure and let the top head vibrate more freely since the bottom head was restricted. So.. even with two 2" holes, not a lot of difference.

Where I do notice some audible difference is when I turn that drum on it's side and play it traditional (looks funny playing a 32" drums sideways). I almost hear an echo like I hear one head hit and then the other says me too!! .. but slightly off... covering the ports takes this delay away.

When I first started building dunun I put a small, 1/2" to 3/4" hole centered.. just because I had seen others do it. I don't bother with the hole anymore unless its asked for.

Michi, you said that the dunun raise in pitch on a hot day. I've noticed the same. Actually coming back from festival, and most recently DrumStrong where the dunun stayed out all night, they went from in tune, (morning) to a little high when it started to get warm to way low and almost floppy when the dew set in about 2am or so. Then the next day around 2pm it was 80 some deg. F. and the drums were tighter than ever... so Temp and humidity definitely change the pitch. But I was always under the impression that it was the skin that would tighten and loosen. It seems that the skin would flex and be more dynamic than the rings or the shell. I can see the shell and rings expanding slightly over several days, but to change so much in such a short time.. I always blame the skin.

[michi]

I also was thinking this would help release the pressure and let the top head vibrate more freely since the bottom head was restricted. So.. even with two 2" holes, not a lot of difference.

Interesting, thanks for that! I suspect that the holes make little difference because their size, relative to the wavelength of the sound, is very small. That makes it essentially impossible for a pressure wave to be affected much by the hole. I would expect that higher frequencies would be affected more strongly but then, a dundun doesn't make many higher-frequency sounds anyway, which would explain the quite minor effect of the hole.

Where I do notice some audible difference is when I turn that drum on it's side and play it traditional (looks funny playing a 32" drums sideways). I almost hear an echo like I hear one head hit and then the other says me too!! .. but slightly off... covering the ports takes this delay away.

That's interesting too. I don't know enough acoustics and wave physics to explain why this might happen. But I'm sure that your ears are a pretty reliable indicator as to the change in sound character

Michi, you said that the dunun raise in pitch on a hot day. I've noticed the same. Actually coming back from festival, and most recently DrumStrong where the dunun stayed out all night, they went from in tune, (morning) to a little high when it started to get warm to way low and almost floppy when the dew set in about 2am or so. Then the next day around 2pm it was 80 some deg. F. and the drums were tighter than ever... so Temp and humidity definitely change the pitch.

Beyond a shade of doubt. Humidity is the more decisive factor. It essentially swamps the effect of temperature. I have played drums in cold and dry as well as hot and dry conditions (desert climate), and cold and humid as well as hot and humid conditions (mountain and tropical climate).

What I've noticed is that the pitch of a djembe or dunun isn't affected by temperature all that much. Yes, they go up in pitch as it gets hotter, but nowhere near as much as they drop in pitch as it gets more humid.

When I was in Mali (hot and bone-dry), my drum was screaming. Then I took it with me on a plane to Ghana, where it was hot and humid and, within a few days, it sounded like a wet rag. I've also played in dry climate when it was quite cold (inland Queensland winter). It's a pain to play in those conditions because it's murder on my hands, and I get skin splits very quickly that way. But the pitch of the drum didn't change that much. I've also played in cold humid conditions (southeast Queensland coastal mountain range, with lots of early morning fog), and it was pretty much the same as in Ghana (only more miserable): drum sounded like a wet rag.

A few years ago, I did an outdoor gig beside river bank in northern New South Wales. That was during summer, but it got a little chilly in the evening, and you could feel the moist air coming up from the river. I had an ocean drum with me that, during the day, had a nice tight skin. At about 9:00pm, I picked up the drum and found that skin was so loose that it actually had a big wrinkle running across it. I could press lightly into the skin it would move by nearly 5 mm. The skin had expanded so much in the high humidity that it had essentially no tension left on it at all.

But I was always under the impression that it was the skin that would tighten and loosen. It seems that the skin would flex and be more dynamic than the rings or the shell. I can see the shell and rings expanding slightly over several days, but to change so much in such a short time.. I always blame the skin.

The rings will expand instantaneously as they warm up. Ever seen images of buckled railway lines in summer? I haven't looked up the expansion coefficient of steel and worked out how much bigger the rings will get with, say, a 15°C temperature change. I wouldn't be surprised though to learn that it might be as much as 2-3 mm.

But I agree. The skin is the most variable factor in the entire equation, especially with respect to humidity. Skins become stretchy and soft very quickly as the humidity goes up.

Cheers,

Michi.

[michi]

The rings will expand instantaneously as they warm up. Ever seen images of buckled railway lines in summer? I haven't looked up the expansion coefficient of steel and worked out how much bigger the rings will get with, say, a 15°C temperature change. I wouldn't be surprised though to learn that it might be as much as 2-3 mm.

Wrong!

I just looked it up. For a dundunba with 20" diameter, looking at a temperature change from 20°C to 35°C, the rings increase in diameter by a whopping 0.1 mm, that is to say, effectively not at all.

My guess was out by a factor of 30. Serves me right. I should have looked it up instead of guessing…

MIchi.

[e2c]

Humidity has so much to do with the pitch changes... we've had some very unusual weather recently, going from warm and dry to extremely humid (close to 100 % for several days, with heavy thunderstorms) to cool and dry... no doubt the humidity will come roaring back tomorrow, since it's June.

A drum subject to those kinds of changes - over a matter of 4-5 days - is going to go through all sorts of adjustments.