I interpreted "all pass" as any filter that is not causing a rolloff. As I used the term, there are multiple all pass elements in all of Jim's crossovers. They include various shaping and resonant circuits which are directly opposed to specific resonances in drivers such that the circuit cancels the amplitude, phase and transient problems of the driver resonance. It actually fixes the driver misbehavior. The fixed driver is therefore prepped to roll in or out at its prescribed slope - high or low pass filter.
These shaping circuits always result in better measurements than the uncorrected driver in all domains. The down sides include cost and whatever electronic veil comes with the extra circuitry. A good listener can hear the effects of the components. Thiel's budgets necessitated mid-level components with mid level artifacts, with the exception of coils. We splurged for 4-9s wire in well made coils. Of course there is room for more improvement there. I am now experimenting with 6-9s foil coils, which are glorious at twice the cost or 4-9s and 6+x the cost of normal production 3-9s ETP copper.
