I was unimpressed by how the extremis bit was incorporated.. Good other than that though.

As i understand it inductive reactance is a mechanism (might not be the right word) generated within a inductor (coil of wire) that changes it's opposition to current flow proportional to the change of ac current or inductance which is just a increase of current itself i would assume, so i was correct in stating that frequency changes inductive reactance.
http://www.allaboutcircuits.com/vol_1/chpt_15/1.html

With current being applied, voltage (frequency) will act as as sine wave if you graph it, when there is no magnetic field present. When the coil is in the gap there is a pre-existing magnetic field which reduces this effect. If the coil is outside of the gap the "sine" wave becomes much more like a square wave since the inductive field being generated is no longer contained. To say that the impedance is changing may be a technical misnomer as you could possibly better characterize it as charge/discharge rates of capacitors.

Back EMF (Lenz/Faraday's law(s)) is the collapse of the inductor-motor circuit as the coil enters or leaves the magnetic gap, which is time/distance related to the charge/discharge cycle of the coil, which is induced by excursion... Voltage/current are related to the time/excursion since they affected the charge/discharge cycles of the voice coil. Lower frequencies often use more excursion to produce the same output level so the charge/discharge cycle of the coil is lengthened significantly, along with secondary EMF (which can be seen as harmonics).

My interest in "extravagant" is to improve what exists, unlike what the rest of the industry seems to be doing. The Audio scene has stagnated for the last 50 years