Size of Midrange Drivers

Why, in this day of super materials, do designers still use
mini midrange drivers?

a midrange driver will start beaming (sound thru it will be very directional pretty much like a focused light beam) at a certain frequency.
The bigger the diameter of the midrange, the lower this frequency of beaming.
For example, when I used to own B&W DM604S2 they had a 7" midrange & the frequency that the Kevlar mid would beam was in the region of 1800-1850Hz.
It was distinctly audible - when I would listen to Frank Sinatra (whose voice is deeper) the vocals would be in line with the speakers. When I would listen to Diana Krall (whose voice is higher pitched), the vocals would pop out in front of the speakers while the other instruments would stay back in-line with the speakers.
I had a long discussion in the AudioAsylum with other B&W owners & found that they were experiencing the same thing.

A large diameter mid is not a good thing - the mid needs to be flat frequency response beyond both the lower & upper x-over frequencies. And, only the electrical x-over ckt should be rolling off the mids i.e. the mechanical failure of the mid should not be rolling off the mids (in addition to the electrical x-over). If this does happen, the x-over response of the speaker will be highly uncontrolled & will be signal dependent. Signal dependent behavior of any electrical or electro-mechanical system is a very bad design. The speaker will have a lot of phase distortion - which means the speaker will impose its distortion onto the music signal & will destroy the timbral & tonal nature of the music. Listening to music thru such a speaker will be a complete displeasure (atleast for me).

8" drivers typically cover bass and midrange to some extent in most 2-way designs I have seen.

3 ways use a dedicated midrange and do not handle lower bass frequencies so size is typically smaller accordingly.

I am not sure that there is really any sound reason why midrange drivers should generally be any larger than they are. You have to trust the designer to make the right decisions in each case.

So not sure 8" midrange size alone really matters that much for mid-range. At least for home applications. Maybe for pro applications in large venues where overall size tends to matter more.

Depends how big is your room and how loud you want to be.
8" or higher midrange driver can push significant amount of air and on the midrange frequencies it's quite a lot to fill with sound small auditorium sized rooms.

Hi Dweller, A few answers....
The obvious, we use a mid range to play mids... smaller than a 4 to 5 inch will normally not play low enough to cover the entire vocal range... many drivers above 5 inch have cone break up or frequency response that will alter the upper vocal range... In an ideal world, a midrange will cover the entire vocal range... No crossover in the vocal region, smooth to no phase shifts and smooth accurate frequency response are most easily found in that 5 inch range.
I have heard very good 15 inch 2 way speakers, this required a 15 that went out quite well and a high frequency driver that would go down and do a good job covering the entire frequency range. So it can be done with many sizes... there is something to say for sensitivity and the dynamics that high sensitivity speakers produce. You seldom find 5 inch mids that are very sensitive 85 to 90 is typical... But there are larger coned drivers that do a good job and it is certainly possible to do a good job with a crossover in the vocal region. As far as Super materials... you can't trump the laws of physics, Mass still cost sensitivity, too low mass still cost low frequency extension and effects box size needed... the super materials have helped with a more detail in our music and lower distortion without a cost to frequency extension. MTM or D'Appolito type designs help give more base output with a small footprint 2 - 8 inch woofers will move as much air as a single 11 inch driver, 2 - 6 inch do move about the same amount of air as a 9 inch woofer, yet still keep the midrange of an 6 to 8 inch... But MTM's do require a very low crossover point from the tweeter to keep from having lobing issues, dispersion issues, smearing of midrange and top notch imaging... I'm sure I'm raising more questions than answering, but about the best that I can do to address your questions, I hope this helps, Tim