I haven't specifically used the 700s but I have tried tons of different nc implementations. And by predictable, I mean "a milliwatt chip can record, analyze, and reproduce an inverted signal in real time". What sounds predictable to a human ear can be awfully complicated when you actually look at the signal on a frequency plot. Audio engineering is hard. There aren't many things that active nc can handle well without horrible distortions. I haven't heard any audio tech that has tried to deal with complex signals due to this effect, which isn't really acceptable in headphones. It turns into a weird digital sounding blips randomly interspersed, occasionally canceling things out.