Wow. None of this is really correct. The morel link is, but there's no explanation.
When a conductor is immersed in an alternating magnetic field, that alternation causes a current to flow in the conductor. A current flowing in a conductor generates a magnetic field at a right angle to the direction of current flow. The voice coil moving up and down around the shorting ring causes a current to flow in the ring which generates a magnetic field that opposes the change in the coil's magnetic field due to the changing coil inductance as the coil moves in and out over the polepiece. That change in inductance is caused by the coil changing from iron core to air core as it moves upward and downward over the polepiece. At high frequency, where the coil doesn't move very far, the shorting ring simply counteracts the coils inductance. AT lower frequencies where the coil DOES move a lot, the ring reduces distortion caused by changing inductance.
It isn't a shield. It's basically a magnetic self-regulating inductance countermeasure. It doesn't increase sensitivity and depending on how it's designed, opening the gap to accommodate its placement REDUCES sensitivity.
Thank you for the articulate explanation!
I couldn't put that into words being I read it on parts express forum at 3am and couldn't exactly remember,
I was just posting the morel link to say that that guy said the ring on morel speakers is for brakes , ( I couldn't resist smiling at that one) but than I talked about a shiny copper ring on morel speakers I wasn't referring to the shorting ring tho I was referring to the top of the bobbin, I needlessly caused confusion to be silly. But anyway ,
Dosent inductive reactance ( reactance from the pole not just plain reactance) in the coil increase exponentially as amplitude is increased? Or is it a linear measurement ? I always wondered about this and coil size ? I also hear term copper cap? That's typically a ring ? Or is it a cap on the pole that does the same thing and just have a band of copper around it ? Pics are great here but you seem to explain things very nicely
Also is it safe to assume based on coil size , and low inductance on any specific driver that it most likely has a ring? I've often compared speakers and look at the TS and notice two speakers that have diffrent inductance ratings but same size coils and they don't state ring or no ring but similar parameters otherwise ?