rainwarrior wrote:
Wouldn't the speaker coil itself filter DC?
No: a fixed DC voltage applied to a speaker coil will cause a fixed deformation from the rest position. At least for speakers that don't include a crossover, anyway.
That's not the real problem with it, though: the DC portion would dissipated as heat in the speaker coil (standard V²÷R) which is just wasted energy and could plausibly cause the speaker to overheat, especially because there's usually no good way to emit waste heat from inside the speaker enclosure.