Speaking plainly...

Audio is difficult.  This is the conclusion I've managed to come to after a decade or so of practising in the art.  Many systems are good at one or two things, but to cover all the bases is incredibly hard.  Being pragmatic is to decide what particular aspects are most important to you, and to focus on achieving those primarily.

Take my speakers, for example.  I'm certainly not a speaker designer by trade, but I know what's most important to me... low distortion and an even tonality with no undue emphasis, particularly in the upper midrange.  I also hate cabinet colouration, which led me to come up with a speaker with no cabinet, or baffle for that matter.  Throwing away these things greatly hurts efficiency and creates potential nulls in bass response, but that is the price that needs to be paid for a small, relatively light footprint which doesn't suffer from the usual smearing of sound as the cabinet resonates.

Losing efficiency in one area of the design like this requires high efficiency, high power handling units to compensate for the shortfall.  I've long since used Lambda Acoustics TD15M Apollo for mid/bass duty (a big 15" unit with stupendous power handling and a curvilinear cone for wide frequency response) but the thought occurred to me that it could be used for a pure midrange.  With the Raal ribbons on top, that is potentially a 95dB/W midrange upwards block, which could be driven by its own small amplifier.  No baffle step compensation should be necessary here, as that can be incorporated into the bass driver crossover, which will have to be driven relatively hard to achieve any bass.

I had been mulling over the idea of a baffle-less speaker for a while, but this created a problem... how to support the drive units?  A bit of a discussion was had with a talented carpenter called Russell who's turned some of my (rather poorly drawn) ideas into reality before, and eventually settled on the idea of a V shape as a support.  This had a potentially interesting property of dividing the rear wave energy, which may help ameliorate nulling problems to a degree.  He builds out of thick birch plywood, which is an excellent material acoustically - a light year away from the typical MDF used in most speakers.

The magnets of the drive units neatly slot into the supporting holes.  The idea was to bolt the drive units together, but in an attempt to reduce transferral of energy through the front baskets, oil-based clay was used to cement the units into the mounting holes - this proved sturdy enough to support the drivers, with some sorbothane spacers keeping things at the right height.

I haven't said much about the 15" bass drivers so far, which are high Q units similar in design to the TD15Ms... I had a bit of a trial with them, discovering that one unit had a cracked basket long after I'd purchased them - the speaker company in question was not particularly helpful in the matter, but thankfully I was able to epoxy the basket to what appears to be adequate strength, and distortion performance appears unaffected.

As said, the nature of the design means that the bass drivers need to be heavily equalised in order to produce any reasonable bass.  In the case of these drivers, a low pass filter was pretty much all that was needed to bring things into line, after attenuating the midrange+HF suitably.

The attenuation of midrange+HF to get a decent bass response worked out to approximately 12dB, which really isn't too bad, although does mean the effective efficiency of the bass driver has been reduced to roughly 78dB/W!  With roughly 200W power handling, that is enough to play reasonably loud, but it won't blow the house down... that was not on the requirements list.  :)

The crossover is relatively simple... second order on the bass driver, first (high pass only) on the midrange, and the tweeter is effectively fourth order, if memory serves.  Response looks something like this, about 15-20 degrees off axis...

It's a fairly even response with mainly dips rather than peaks, and a gentle roll off at the top end unless you're sitting bang on axis... the limited vertical dispersion of the ribbon is a bit of a price to pay for the excellent sound quality it provides, though this could be ameliorated with an "ambience tweeter"... something I've been meaning to try for over a year now but haven't got around to!

Once the crossover was gotten into a reasonable shape, I stopped messing with them and just started to listen to music... which is how it should be, really!  They have their limitations (primarily the small sweet spot), but perform well with a wide range of musical genres.

The big gap in efficiency between bass and midrange+HF suggests biamping would be an excellent idea - perhaps a high efficiency Class D driving the bass, and a high quality small Class A driving the midrange+HF.  Now there's a thought...