I am going to make holes in it to connect the two hemispheres which will hopefully help break up the internal spherical shape. Also it will have a bolt thru it to clamp the lower hemisphere to the ply and threaded rods put through it and the mid bass mounting holes for the top hemisphere so both hemispheres can be clamped down against the ply in the middle. That should be enough to stop any ringing in the steel but as long as the cut edge of the hemisphere is touching a surface it doesn't ring at all. The last reason to use some wood is to mix up the materials used a bit. I plan to use ply for the leg(s) and baseplate if required.
The only joint in the enclosure will be where the two hemispheres join each side of the plywood spacer. There will be no glue and the clamping of the hemispheres to the ply via bolts should keep it in place. I have to make sure there are no air leaks of course. It will be easily dismantled so if I ever need to change anything inc driver then just need to swap the top hemisphere or one other part.
It should be a super rigid structure due to the strength of a sphere especially in 3mm steel. I am looking forward to what effect this has on the bass which needs rigidity and no bending of panels to be as efficient as possible. Well there are no panels as such. I am expecting this to be a major advantage over the traditional six sided wooden enclosure.
I am also very much looking forward to the effect of having the mid bass in a sphere. As the mid bass is running fully open up to about 7kHz before it rolls off acoustically then I expect there will be benefits from the spherical enclosure. It will hopefully make for a smoother sound as the ripples in response should be vastly reduced. Look at that lovely flat line for the sphere. About the worse thing you can do is put the driver in the middle of a square or circular baffle.
![Image](https://i.imgur.com/wDxJyl6.gif)