Originally posted by Graham Maynard
Thanks for your reply - very clear.
I still can't help thinking that cone drivers used for anything above bass frequencies should be elliptical, and not circular, in order to reduce errors arising due to radial symmetry.
I don't know if they'd be any better in that regard, I could only speculate. However, it would introduce other tradeoffs. For best horizontal polar patterns the long axis would have to be oriented vertically. This then forces the CTC distance to increase, exacerbating the lobing in a multi-way system. The length would cause the vertical off-axis of even a single driver to have phase issues (worsened directionality) at lower frequencies.
If you orient them with the long axis horizontally to improve vertical spacing and lobing issues, you can reduce CTC, but then you'll have the same off-axis phase issues in the horizontal plane.
You wrote >>
A ring of energy closer to the former has less total contribution to the total output of the driver at that frequency than those farther away. <<
Yes, and I see this as a situation where the centre radiation of a cone driver can become cyclically lagging/leading wrt to the cone, thus another reason for peaks and troughs developing with changing higher frequencies, especially with full range drivers.
Precisely. This is just one of the tradeoffs, especially WRT soft vs. hard cones. Soft cones can be designed with curvilinear profiles and materials/damping such that at higher frequencies the damping is improved with some intentional flex "breakup" that actually allows the area closer to the former to radiate with damping reducing it away from the former. This provides an effective "ring" radiator to some degree. It helps to extend the top end and improve directionality. I'm partial to doped paper myself, though the ceramic cones (Accuton) may be a close second at this point.
Hard cones don't do this. They flex far less so more of the cone radiates at all frequencies. This results in the extreme breakup seen in them.
Full range drivers have additional tradeoffs to essentially incorporate a tweeter in it. One of them must be increased IMD (Doppler) due to the close coupling of the woofer with the whizzer tweeter. There's no way to produce bass without highly modulating the high frequencies from the whizzer cone. Plus, resonances in the main diaphragm may affect the whizzer and vice versa.
It's all about what tradeoffs the designer desires.