I'm so glad you are interested in full rangers. I have written on these forums at length about full range speakers.
You are absolutely correct that the mid range of a speaker must be perfect. Unfortunately t is so often necessary to have a crossover in the speech discrimination band. Crossovers introduce time shifts and disconnect fundamental tones from their harmonics in time.
The problem is that no one has achieved pistonic motion throughout the frequency range, and so cone break up has to be accepted and designed into the driver. So roughness in the upper frequencies and poor off axis response is all too common.
All designers should be full rangers at heart.
I have a long association with the
Jordan Watts module. I still think overall this unit still has the smoothest response of all the full rangers. The Mark Audio drivers are its direct descendants. In may respects improved, but a little hot in the top end.
I have a fully worked up a design for two of these
Mark Audio drivers in a TL with
this tweeter. Although strictly speaking not a full ranger, to all intense and purposes it is. It is an MTM design with the break up dealt with and and the phase shift kept to no more than 90 degrees, so it is a phase coherent speaker. It models ruler flat, and there are only four small components in the crossover.
I really don't have the energy to build a pair of these right now. If you are interested I will make the plans available to you.
F3 is 40 Hz, and since this is a true TL an not mass loaded it is only down 15 db at 20 Hz, and only 8 db down at 30 Hz. Power handling is 100 watts and sensitivity would be 94 db 2.83 volts 1 meter.
This would be a highly cost effective speaker, and likely one of the very best around. If you would consider building a pair of these I would be very grateful.
If you are interested I will send you full details.