I don't think they would be particularly helpful for sleeping. Firstly, they would need to have very good microphone sensitivity to detect the (very?) low freq

I don't think they would be particularly helpful for sleeping. Firstly, they would need to have very good microphone sensitivity to detect the (very?) low frequencies or at least the low sound pressures of those low freqs. Also, when I tried the new big Sony noise canceling headphones (very highly rated), I found the sensation somewhat unsettling. They did indeed shut out practically every external sound (in a big store, not at home in bed), but I perceived some kind of constant subtle positive air pressure in my head similar to what you feel about half a meter under water. My solution now in the rare case where I'm in a location that bothers me is to use some low speed fan to create lower frequency white noise. Also, either I've been luckier the last few years where I've lived or I'm becoming less sensitive to it, because I don't get bothered as often.