Essentially a line is cut across the bottom of a gas cylinder continued about 300mm (since imperial people rarely include metric measurements, here it is back at ya) up the sides with the cut being on opposite sides on the way up.
This splits the lower end of the cylinder into two and when given a decent hit with a striker of some sort (wood is best), will ring loud and long and if made with care, in tune.
Since I had a well out of date SCUBA tank lying around I thought it absolutely vital I made one of these and at the same time, my first instructable - please forgive phone camera.
What you need:
An empty gas cylinder - scuba, oxygen etc. This may work with a round tank but I have only done it with a long cylyndrical one.
Angle grinder and a few 2.5mm cutting discs
Maybe a hacksaw (with a spare blade)
Dressmaker's tape measure or builders tape measure and a piece of string
A marking pen
2 saw stools (to use as a jig)
Spirit level (if your work space is a bit uneven)
Chalk line (optional)
I just noticed something about the video. When the tank is spun rather than going wow - wow - wow, every time a cut passes, it goes wow wow - wow wow - wow wow one wow as the cut approaches the front and one as it departs the front, reinforcing the idea that the wow doesn't happen when the cut is right in front of me. There must be an explanation for this.
A couple of words of caution that should be obvious, but here they are anyway: Make sure there is no pressure in the tank you are going to use - open the valve, leave it open, maybe even remove it. Also, if the tank has been used for any sort of flammable gas, release any pressure, remove the valve and fill it with water (then empty it) before cutting.