Aluminium Bottle Udu - Demo and How to Make (use headphones/speakers to hear deep bass)

I used 5.5L aluminium bottles that I got from here:
https://www.awo.com.au/aluminium-bott...

Here's a similar bottle for anyone in America:
https://airseacontainers.com/1-half-g...

Here are some bigger bottles up to 27L from China, but you have to buy at least 10 of them:
https://www.alibaba.com/product-detai...

The bottles are kind of hard to find, but they seemed to be used commonly for essential oils and pharmaceuticals.

HOLE SIZE
I made the hole 40mm in diameter, but I don’t think it particularly matters since it doesn’t affect the pitch of the bass tone. It mostly affects the volume, so as long as it’s not too small it should be good. It does affect the pitch of a resonance that is present whenever you strike part of the bottle, so you could tune that if you wanted. In my case, the bottle happens to produce a very in-tune bass note of Ab, and resonates at an F with the hole uncovered, though I could probably bring that up to an Ab as well by making the hole a little larger.

HOLE PLACEMENT
I placed the hole nearer the bottom to make the flat playing surface more accessible, but I didn’t place it too far from the middle since that seems to be convention. Playing the other opening at the top of the bottle produces a very weak tone, so obviously hole placement is somewhat important and it probably shouldn't be far from the middle.

HAMMERING
For the hammering, I was just experimenting and going slow with the hope that I’d end up with something better than where I started. I was expecting that the pitch would go up and become more dampened, which is basically what happened, though at first the pitch actually went down a bit when I hammered around the edge, which I found interesting. Hammering compresses and tightens up the metal, so it makes sense for the pitch to go up if you think of it like a drumhead, but it’s obviously more complicated than that when you have different parts of the surface under different amounts of tension. Steel drums use that idea to isolate different parts of the same piece of metal to precise pitches, and they can even tune the overtones, so maybe the answer lies there somewhere. Cymbal hammering also uses the idea of creating many different areas of vibration to create a wash of harmonics, and large dents can be used to create intentional dead spots that break up the surface to make the sound more complex, but also more dampened. I had those two approaches in mind and I tried mostly gentle hammer strokes with a few much harder ones around the edge, but I was really just messing around. I don’t know how much you could expect out of aluminium, but I was happy enough with the improvement and learnt something from it.

HANDLE
The handle on the bottle makes a nice click, so I taped piece of foam to it to keep it a millimetre or two off the bottle so it doesn’t rattle

BRUSHES
I made a detachable brush for one of the udus from some old guitar E and A strings. They’re loosely coiled up so the ends don’t cut or unravel. They’re attached with velcro, which is superglued to the aluminium. I got this idea from the Valter Percussion Aludu, and I think his version works a bit better, probably since his brush is on a flat surface. https://www.valterpercussion.com/prod...