[Telecolor 3007]

Did you ever encountered radios with this kind of speakers? (maybe some tv sets used them too). Electromagnetic where the ones that didn't had a magnet, but a electromagnet in stad (not to be confuses with alsmost the same principle, but that had "funnel", like in old cartoons).
The high impedance ones (700-800 Ohms) where made so it will be no need of a audio output transformer (which needs to be of good qualty if you want a good sound)... dizavantage: the coild wire was thin and could get broke.