I don't really get your question, what do you mean by "ANC going crazy"? And if you mean "reducing the bass", which is how I interpreted your first post, how could people know if the thin bass is caused just by the lack of seal itself, or some ANC feedback loop? Anyway, a Sennheiser rep has already stated in this thread that an ANC off toggle feature is never going to happen for the M2. I guess they use some sort of integrated hybrid BT/ANC chip.
5/4/15 at 11:05am