i already did a writeup on Subwoofer drivers here:
now time for midrange drivers …
basically a cone driver conceptually operates in three frequency regions … in the lower of the 3 regions it is dominated by interaction with the enclosure subject to TS parameters … in the middle of the three regions it is still subject to TS parameters but is now effectively an open baffle situation as we are far from port and fundamental resonance … and in the upper of the three regions the driver is dominated by cone breakup, voice coil inductance and beaming …
if we call these regions A, B and C ( my terminology for just this discussion ) then Subwoofers are optimized mainly for region A and to lesser extent region B … woofers mainly for B and to lesser etent A and C … and midranges optimized in roughly equal parts for B and C …
B is pretty simple - in this range the cone moves as a piston, box effects are irrelevant as are all other complicated effects - it’s just a matter of motor force, cone area and moving mass - you want more motor force and more cone area and less moving mass - very simple
if only everything in life was this simple …
but unfortunately even a midrange driver is only pistonic to maybe about 500 - 1000 hz but and then it goes into breakup and starts to suffer from other high frequency effects which must be controlled …
some effects midranges must control for
- inductance
this can be handled simply by having a short winding depth - a smaller VC will automatically have lower inductance. but if that is not enough shorting caps, rings and sleeves from copper or aluminum can be used to reduce inductance further.
- voice coil mass
again simply using smaller VC can be enough, but also using aluminum voice coil wire is common for midrange drivers ( aluminum is 1/3 the weight of copper ) and also using thinner wire as well. to compensate for extra resistance of thin aluminum wire midrange drivers use higher magnetic field densities and shorter VC overhangs.
- breakup
cone geometry, composition, ribs etc can be used to control breakup …
- suspension resonances
the type of surround used has a profound effect on frequency response and perhaps beaming as well
essentially in breakup the cone acts as a bending wave radiator and the goal is to balance the stiffness and damping of the cone against voice coil mass and the termination condition at the boundary presented by the surround … these plus the inductance are all balanced against each other until acceptable frequency response and beaming characteristics are achieved …
while optimizing these factors compromises in other areas may be necessary. for example motor force may be sacrificed or suspension compliance or linearity or cone strength and so on.
again, as i said before, i think having midrange cone, woofer cone and subwoofer cone is a good way to optimize for a division of labor so to speak across those 3 frequency bands. midrange can focus on the breakup and inductance effects. subwoofer on port and box tuning effects. and woofer simply plugs the gap between the two. although you could optimize a single driver to do it all you would be making some compromises, which only really makes sense in small, low cost and low output systems.
so as i said before perhaps 21" subwoofer, 15" wooer and 8" midrange would be a solid modern classic setup so to speak.
above the midrange at about 1 khz you could go to a 3" or 4" titanium compression driver and then at about 8 khz to a bullet / slot supertweeter.
such a system would outperform basically anything you can buy at any price simply because it would be based on sound scientific principles instead of marketing hype and aesthetics as basically all “Audiophile” speakers.
if i wasn’t a sick bastard i would just build it and call it a day but i want something even better …