Your views are welcome. I watched your video and i appreciate your views but you have not told me anything new, and the way you try to explain things is not exactly correct either, as most people, you lack laser precision, let me elaborate on it.
Firstly, if you look at my first post you will see the formula for inductive reactance.
XL= 2πfL
So obviously and i have spoken about this many times, smaller the inductance smaller the reactance aka self-induction. It is also clearly implied in my last post that voice coil has low inductance and low reactance and thus needs ohmic resistance to limit the current, especially at low frequencies, all written clearly.
And obviously air core coil has lower inductance than one with iron core, i don't think you had to make a video to show such obvious and widely known basic thing but on the other hand why not, i like the video.
In any case, you said in the video air coil has no self-inductance, well it does, just less. I think you know that and you just expressed yourself like that. This is related with the common formula E = 444 f NAB volts rms. Also, you repeat multiple times how without core coil supposedly "cannot complete the induction path". This is wrong. Flux always closes on itself, with or without a core. Key reason is iron core amplifies the magnetic field, not just providing the path of lesser reluctance, so
B = μH
aka flux density is permeability of the core times magnetizing force
or longer formula
flux density = amper x turns x core permeability x core area / m² (T)
and magnetizing force H is closely related to popular term ampere turns, namely
H (magnetizing force) = ampere x turns / length of a coil
And to further elaborate on self-induction....
Obviously self-induced voltage prevents current to flow instantly, i and others spoke of this many times here, and another thing i have figured myself and another person here also figured it independently - altho it is commonly said current cannot flow instantly through an inductor for back EMF which prevents instant current to flow to appear there first must be some small current cause without it voltage could not appear - so technically current is leading voltage, well, for a tiny instant. Or maybe it does not, this is only an assumption. In that case it is even stranger as it means voltage across an inductor jumps without change of current through it, something that should not happen. In any case, voltage jumps up to source voltage and then decreases gradually proportionally to 5 time constants of which i have also spoken before.
t = L/R inductor time constant, after 5t (transient time) current reaches 99.5%
Now the reason for the smaller inductance of a voice coil vs transformer coil. Well, firstly voice coils are usually physically smaller than transformers which usually means smaller inductance.
As for the gap, voice coil indeed has an airgap which lowers inductance but if you look how speaker is made you will notice that gap is actually small. It surely does reduce inductance but i would not agree it is the main reason.
https://youtu.be/RxdFP31QYAg?t=86Then, you mention the permanent magnet, of which i was perfectly aware, and you say "also gets complicated by the permanent magnet's field". The thing is voice coil is working against the magnet half of the time so magnet is reducing it's inductance half of the time and other half of the time it is increasing it's flux but it would be incorrect to say it is increasing it's inductance since inductance of the coil is only the part of flux it creates by itself, additional flux can lead to saturation but does not increase inductance, it is but a bias. So it does complicate things but i would say magnet is overall reducing the inductance which is already quite low due to small core size and the airgap.
So, obviously, inductance of the voice coil is much smaller - usually in range from less than 1mH to few dozen mH compared to transformer primaries which are usually like hundreds of times more, for example i measured one of microwave oven transformers pri ind 351mH and sec ind 34H. I also measured inductance of my ~50W speakers and i don't remember exactly but it was tiny. And obviously, as i said before, smaller inductance means smaller self induction. These are simple basic things.
So, all that was clear and implied. But important correction, again, it is not that core allows for "south induct back into the top" flux always closes on itself, with or without a core, it is, as i said above and before, the fact that iron AMPLIFIES the field - altho mainstream still sleazily forces the term CONCENTRATES the flux instead of AMPLIFIES. Altho they are forced to admit flux is larger, up to a million times, with the core.
Obviously, larger L means longer time constant, so it takes longer for current to rise to max value and if you wanna force it you need more voltage, that is, more power, unless you are smart and you use the nature given parallel RLC i spoke of in the thread of same name.
As for your comment on "Speaker doing work", it seems you are confusing the reactive and active power. If you removed the coil from the speaker inductance would be even smaller and since the ability of a coil to do work (power) is flux times frequency (just like motor is torque times rpm), you would have to increase number of turns significantly to get the same inductance and same ability to do work but more turns means more ohmic resistance so your losses would go up. If you would not add more turns, current would be larger, obviously, you would again waste more power as heat in accord with P = I²R copper losses and would do less work. So of course air core coil is not optimal to do work.
So, one with iron core is of course more efficient, but not overunity. Conventional relation here stands, unless special configurations are made. So no magic there just by adding a core. Magic happens when you go into resonance or when you play with flyback aka collapsing field backEMF etc. Using the coil in classical manner, just like electric motors is surely not overunity, no matter how much iron or exotic core material you put.
Or to sum all this up in few words, of course inductance of a voice coil is less, this is obvious and clearly implied. Iron amplifies flux but this does not automatically mean overunity. It can and does lead to overunity in specific cases.
Nix
