I currently have a project on the go (though it has been dormant for a few years) trying to build speakers better than my existing PMCs (EB1i). It is rather a long term thing due to availability of time and the complexity of build (and rebuild) with inherent trial and error. However, a part of the design was to mount the mid and treble units in satellites that would sit atop the bass cabinets, maximising flexibility, and that I did early on.
The midrange drivers are of particular interest and the linkpin for this post, being ATC's wonderful dome units (SM75-150), that will be known to anyone who has heard them. The satellites are shaped to hug the drive units tightly, elegantly 8-sided from the front, tapering more towards the top, 300mm tall by 200mm max width and only 115mm deep, but weighing 7.5kg (such is the weight of the SM75). An easy part of the project, I built them some time ago - but it has only just occurred to me that I might be able to partner with the EB1s and improve what I have even before doing anything more with the project. So that I have just tried......
I set out with the project using active tri-amping, as it is easier to tweak an active crossover than a passive one to get levels and phase correct - so that is what I used for this trial, with an old ATC EC23 analog unit*. Amplifiers are a pair of Musical Fidelity P170s covering mid and treble and a P270 on bass.
After initial setting up, balancing levels and phase, it was time for some listening - though no time for anything extended, just a few tracks. First impression was that it was indeed an improvement - and the measurements from setting up using REW software showed lower distortion than the PMC: remarkably low.
I was concerned there may be a downside as the EB1s are 1200mm tall so the satellites on top place the mid and treble units at about 1300 and 1430mm respectively, rather a bit above normal seated ear level, though lying on their sides would bring both to 1300. I found I preferred them on their sides, with tweeters on the 'outside'.
This assessment has only been considering the mid and top end, as the bass is still through the bass section of the EB1's crossover. Whilst I am convinced that the ATC mid is the prime reason for the improvement, the other variables need ruling out, viz. active vs passive drive, and different amps compared to my normal usage. So, As well as extended listening I also need to remove the crossovers from the EB1s and compare them with full active tri-amp drive. If the difference is how I think it will be - improved but not as much as with the SM75 - then it is likely the satellites will stay, though they will then need finishing cosmetically!
So, for anyone with PMC speakers having great bass but mid just that bit less than in some top models, this could be a way to achieve nirvana.
The cost is far from cheap - about £1200 for the drive units and protection capacitors alone makes the satellites as costly as many people's full range speakers, while tri-amping would be ridiculously expensive if I wasn't using gear bought cheaply secondhand - but the result......
I will feed back further once I've had time to evaluate mor fully, though that will be some weeks.
*I also have a Behringer digital crossover unit which allows even more flexibility, which some time I'll try swapping with the EC23.