thx best,
I don't know the Rythmik products. Servo controlled is another factor. Theoretically, according to Doug Blackburn, I would predict a servo 12" would still integrate better than a servo 18". But it would be an apple/orange comparison when comparing a non servo 12 with a servo 18.
As an aside, in 1980 I heard the HQD system--double Quad 57's, Decca ribbon tweeter, 24" Hartley woofer built into the floor whose cabinet was the room below. The Hartley was probably not servo. Those Quad electrostatic are still unmatched for midrange accuracy, and probably for upper bass accuracy. I don't listen to music with much deep bass, so I couldn't comment on the quality of the bass from the Hartley. Mark Levinson, who put together the HQD, drove it with triamped Levinson ML2 power amps and used crossovers to keep the midrange overtones from the H out of the Quad midrange.