Don't know about you but I'm getting sick of this thread
And the possibility that I am chasing something that can't be achieved.
Anyway, further messing about. I replaced the HDPE balls with the steel spheres. I did not put the foam back as I thought it was choking the openness of the speakers. The bass was also too low in level for my liking too. I did it because thought the midrange was too prominent. I have however put some 10mm thick fluffy stuff that came out of an old car seat over the spheres.
A change in presentation has obviously occurred. Two things have changed - steel spheres instead of plastic and much less stuffing between the mid bass cube and the sphere. Well, bass levels have increased I am happy to say and the mid range isn't headache inducing like it was.
The steel spheres are obviously not elastic like the plastic ones so that may be responsible for bringing up the bass. The open cell foam was 75mm (3") thick and whilst reducing the midrange it was strangling the vibrancy of the speaker.
I may be able to get away with no stuffing material over the steel sphere and will try it in due course. It seems like the tweeter pod lowered down closer to the up firing mid bass is still sounding good although issues sometimes arise later on after much more listening or something else changes.
I expect things will all change when I get the mid bass drivers in a sphere. At the moment the crude horn shape is flat on the underneath of the mid bass enclosure and curved on the top of the steel sphere resting on the floor. Like this
There will be some reflections going on which is what the issue with horn resonances is all about.
When the mid bass enclosure changes to a sphere then it will be curved on top and bottom with the only difference being one has a driver in it and one doesn't. Like this
There will be much less reflection going on with both sides being curved . I expect that to sound better
So it looks like if this design stays the same going forward then I need to buy another four steel hemispheres. I think the rigidity of the lowest sphere is going to be just as important as the rigidity of the mid bass enclosure.
The placing of the steel sphere under the down firing mid bass has had a positive effect in that the bass is stronger, more tuneful and punchier than the plastic sphere and the evening out of the bass frequencies is still occurring, probably even more so.
Well chuffed so far.