I've only heard Lowther. They were used as giant midranges In a 3 way horn system. Besides crossovers, they also had transformers. Also heard Supravox field coils in another system. Don't think they used whizzer cones. Both systems sounded great.
Don't understand how whizzers work. If the main cone can't produce high frequencies, why would adding a whizzer help? Hasn't that added even more mass to a driver that weighs too much to reproduce high frequencies?
Thanks,
aldnorab