Bob 2
The next step was to install the correct drivers, so I bought a total of four Seas Excel W22 midranges and a pair of Seas Millenium tweeters. The Millenium can be crossed over at 1440Hz, and the W22s are very clean up until the point they disintegrate. Others have used the cheaper HiVi M8A with nice results, but if these drivers are good enough for SL, they are good enough for me.

To dampen resonances and rebate the drivers, I covered the front of the baffle in 6mm nitrile rubber, available from your local rubber emporium. It also looks pretty good.

This combination was smoother than the first Bob. Very nice.
I then covered the bass panel with nitrile rubber and rested. It had been a long day. The bass with the Focal 10L6411s was what I had expected from a dipole - very clear and open.

However, even these two 10 inchers don't have the xmax to give the depth and power I was after. They sounded great down to 40Hz, when I crossed over to my sub, but I wanted more more more.

I wanted Bob to annoy the neighbours.
And so I pulled out the Focals and replaced them with a pair of Adire DPL12 dipole drivers per side. The DPL12 is a specialised 12 inch dipole driver. Hence the name DPL12. They have good xmax, very low Fs and a total absence of the noises you sometimes find with open air drivers.

I mounted them push pull, which means one driver fires out and one in. Each coil is wired in series and each driver is wired in parallel. This is all supposed to reduce distortion.
Another shot of Bob's Butt, but with the DPL12s.

The bass down goes down to 20Hz flat, with reasonable if not excessive power. I have a couple of tracks that will bottom them a high levels,but generally they are fine even with organ music.

In fact, they sound great with organ music.