[PAR_WIG1350]

If I had to guess, It started with two separate discoveries. First, the discovery that a moving diaphragm could pick up and reproduce sounds (ears and drums are respective examples that are respectively naturally occurring and well known throughout history). The second was that a current traveling through a coil can move things. Anybody passing a current through a long wire that had been coiled to keep it organized could have discovered this if there was any iron or magnetic material around, a compass would work too. Then the two were put together and the transducer was born.