I've always wanted to know what a "field coil driver" is, anyway. Can anybody enlighten me?Instead of being generated by a permanent magnet, the magnetic field within which the voice coil moves (the voice coil being what conducts the audio signal) is generated by a DC current flowing in a different coil, referred to as the "field coil."
Field coil speakers were used in many radios of the late 1920's and the 1930's, before permanent magnet technology came of age. Those included high end radios manufactured by companies such as E. H. Scott (no relation to the hifi manufacturer H. H. Scott, who came later) and McMurdo Silver, which can be considered to be precursors of modern hifi systems.
I believe that the main theoretical advantage of a field coil driver is that there is less variation of the strength of its magnetic field as a result of vibration and perhaps other effects related to the audio signal.
Regards,
-- Al