One thing that happens when you biwire your loudspeakers is that the input of the high- and the low-pass filters are fed with different input signals. The difference is a result of the high frequencies and the low frequencies being forced to travel different paths, perhaps through different types of cables, but under all circumstances through cables who have seen different loads (a tweeter with a high pass filter has a completely different impedance response compared to a woofer with a low pass filter!). What happens is that the drivers will work less well together than when their filter halves were fed with equal signals. The result is a generation of more static and stochastic phase error sounds at different directions from the loudspeaker. The stochastic phase error sounds appear because there may be different types of unlinearities in the low- and high-frequency paths. What does this sound like? Well, usually, just as you may expect from physics, it appears as a change in the reproduction of space and sound stage. Often, the first impression is that the "biwired" sound presents extended "dimensions", more "air", and is more "living". The impression after a week or month, however, is that all recordings sound very much alike, and the "airiness" appears on all records. It does not even sound like air anymore, instead more like a slime that pollutes every record you play. No wonder, since it is not a real, recorded quality but a "speaker characteristic" added to all reproduced material. "Sameness" is another word for it. Picture 4: This simulation is based on the diagram of picture 3. Here you can see that a phase difference has arisen when biwiring is used. The reason why the phase difference is largest just above the cross over frequency is that the inductance of the cable resonates with the capacitance of the high pass filter when not the inductance of the low pass filter is available in this range as when single wire is used. The most probable reason to the capricious sound of biwiring is that on top of this steady state error another, transient induced phase error between the cables will appear when playing music. This changes the radiation pattern of the speaker with the music. The human ear is very sensitive to such phenomena.