Eli5 – Why are drums round? Is it something to do with the shape that determines the ability to hit something and get a percussive sound out of stretched materials?
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Drums are round because it is easier to stretch the drum head over a round shape without collapsing the sides of the structure like a square or rectangular box would. And the head needs to be stretched in order to act like a spring and bounce back to flat after being stuck, thus creating the resonating sound with its bouncing.
A [Cajon](https://en.m.wikipedia.org/wiki/Caj%C3%B3n) is a decent instrument, but the striking ‘head’ is a thin, semi-rigid sheet, usually a plywood panel, so it doesn’t need to be stretched under tension to hold its shape.
Your premise is wrong. There ARE square drums: https://tqdrums.com/en/products/bass-drum-testa-quadra/
Having that said, we probably see many more round ones because, as mentioned before me, they are much simpler to make
My thoughts.
1. Easier to make and stretch evenly.
2. The membrane is mentioned to produce kind of a basic harmonic wave. Other formes of a drum will produce more complex sound spectrum.
On a round drumhead the stress is spread evenly when you hit it.
On a square drumhead about 70% of the stress is distributed into the corners, leading to a much weaker drum.
Since the drumhead should be round it follows that the rest of the drum tends to be round. Percussion instruments where the striking point is made out of different materials (such as laminated wood) tend to have other shapes since the stress is distributed differently in materials with a strong direction (like wood).
You know how when you pull a rubber band tight, and flick it with your finger, it makes a sound?
A drum head is basically a hundred rubber bands squeezed together.
You want them all to be the same length, so they all make the same sound. If they are different lengths, not only will they make different sounds, those different sounds will actually fight with each other and cancel each other out, and the result won’t be a sound that is fun for anyone to listen to.
People saying about stretching the drum skin are correct. Square drums exist, such as a [cajon](https://www.google.com/search?q=cajon&client=ms-android-samsung-ss&prmd=svin&sxsrf=ALiCzsb-vCkyro1hy6Bg7N5fLtXhoIajXw:1668885694369&source=lnms&tbm=isch&sa=X&ved=2ahUKEwig4u7X-7r7AhWBSEEAHf8cAiQQ_AUoA3oECAEQAw&biw=360&bih=670&dpr=3), and are usually a wooden material instead.
I absolutely cannot Explain Like You’re 5. However, a very interesting approach to this question is summarized (also not like you’re 5) in the Wikipedia article here: [https://en.wikipedia.org/wiki/Hearing_the_shape_of_a_drum](https://en.wikipedia.org/wiki/Hearing_the_shape_of_a_drum).
So the answer is that, no matter what the shape of the drum, you’ll get a sound. (If not, basically all of physics doesn’t work.) The question is “what sound?” Since any function can “obviously” be decomposed into a sum of sines and cosines, this is just a question of Fourier Transforms. (Note that Fourier wrote that this was obvious over 200 years ago and it’s still one of the hottest areas of mathematical research. When a mathematician writes that something is obvious, it sometimes opens up thousands of jobs.)
It’s all about time. As in: how much do you have to spend tuning your fancy square drum? Round ones tune up quickly and reliably. Square skins are much more finicky.
There is one square drum with a skin head I’ve heard of. It has different names but I forget them all. It originated in Jamaica according to this Aftopop episode I heard. But yes harder to stretch evenly, tun etc.
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