Richard,
The driver itself is very much in the signal path, so there can't really be a valid catch-all statement that a doped or mechanically controlled driver doesn't degrade the signal, but an electronic component will, or even whether one is better than the other without context.
I would also dispute that only single driver speakers are capable of a coherent presentation - that isn't my experience, but I'm sure others may perceive this differently.
Regards,
Alex
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