Spatial Audio Labs

@lewm, being a Beveridge guy would you care to join in?

The most difficult part of a loudspeaker to manufacture is the enclosure. The reason big ESLs are relatively inexpensive is that they do not have one. It is much easier to make a simple plate so Spatial can make a very competitive loudspeaker and probably make more money doing it. I myself have made several open baffle speakers for friends pairing them with sealed subwoofers which brings us to the problem, bass. There is no sub bass. As the wavelengths get longer they simply cancel out. Above that bass performance depends entirely on the room and how sound bounces around. In the right room these speaker can sound very bass heavy. Distance from the wall is also important. Having measured X3's I can tell you there is no way anyone will get remotely flat bass response out of them even with room control. But bass can be very difficult to evaluate. people can "hear" the note even with the fundamental missing. 
Our brains fill in the blanks. 
The best way to use these speakers is with subwoofers crossing up a bit higher at 100 Hz at least. This will dramatically clean up your midrange and give you controllable bass as low as you care to go. This is not much different than any dipole loudspeaker as they all have the same failing.