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1 $begingroup$ Modern Speakers have permanent magnets and are called PM speakers.Permanent magnet materials technology has improved a lot over the last 80 years .Around WW2 EM speakers were common because permanent magnets were not as good as they are today .The old school EM speaker had the usual voice coil and a wound electromagnet where the permanent magnet is today .The electromagnet wasted a lot of power .5 to 10 watts being typical .This DC power burn was often more than the audio output of the radio .Mains radios had electromagnets wound from many turns of very thin fragile copper wire giving a coil DC resistance of about 1000 to 2000 ohms .These coils would fail open circuit meaning that you wont see many of these today .Car radios would also use EM speakers with low resistance EM coils to match to the 6V