High-purity copper wire wound around a Permite core + discs - Jantzen Audio.
Extremely low DCR which does not alter driver damping factor and add to loss of efficiency.
The non-ferrite core/disc material provides significant lower hysteresis compared to coils with ferrite cores, at the same time delivering higher power handling.
Generally only recommended for bass & mid section on crossover.
Power handling capability is determined by core/disc size and wire thickness.