IF, as you say, the tubes don't "know" what they're driving, then we should be able to substitute an electrically equivalent black box in place of the speaker load, and expect the very same response, right? at least in terms of the amplifier's output voltage/current characteristic?
indeed, the chart provided by mr coil backs that up.The impedance curve of a fully unmagnetized speaker must be its DC resistance plus whatever loss/parasitic inductance the voice coil has.
Note: a magnetless speaker will be flat; a weak magnet one will not; the HF part will always be about the same but the resonant peak and the "Q" will not.
hopefully the "reduced magnet strength" method manufacturers (and i say that because it's both fluxtone and FDM) take that into account and either de-rate their voice coil wattage ratings, or add ferrofluid, or some other thermal management.The voice coil will get hotter, you are right that motion cools it; in fact I already commented here that one employee of mine, probably inmersed in a Jamaican dream or floatin in a sea of beer, has on occasion mounted an unmagnetized speaker mixed with regular ones, the lower SPL was not that much noticeable (logarithmic ear response, etc.) but the cooking epoxy smell gave it away.
i agree they are somewhat counteracting. hopefully they'll cancel each other out!Don't think the screens will be affected, because there are two "errors" which tend to compensate each other: impedance will be lower, because the reactive component will be lower, given a weaker cone movement (the object of this attenuation); yet as you say, the voice coil might get somewhat hotter, raising the DCR; both effects act in opposite ways and will somewhat cancel or thereabouts.
Tube plates and screens should not be much affected.
I leave that test to you or whoever wants to do it.
in my experience replacing reactive speaker loads with purely resistive ones has resulted in premature output tube failure. however, this is not exactly the case here as there is still some inductive component to the load.