Noise isolation where it is a good tight seal in the ear does a good job of blocking higher frequencies but transmission through the physical material transmits lower frequencies.
Noise cancellation in personal non-military class noise cancellation is not able to remove high frequency sounds as:
- the wavelength is so short it is a computationally expensive to calculate exactly the inverse wave, the electronics is not there yet with good battery life
- the most popular use of noise cancellation headphones is for flying, to cancel the lower frequency hum off the engines and the airlines prefer passengers to hear the announcements and instructions from crew.
Probably a mix of a tight in-ear bud to best of noise isolation combined with noise cancellation is most likely to work but you're fighting the conflicting need of computing the noise cancellation inside a bud light enough to not fall out. I'm sure these will come eventually.
In the short term I recommend noise cancellation with white-noise generating as the white-noise reduces the conscious reaction to human voices.
Aircraft engine noise peaks around 400Hz, the wavelength is 0.85 meters.which is order of magnitude larger than the domestic headphone so it is computationally lightweight to compute the inverse sound and do a half decent job. That wavelength is so long that only a small % of the wave is inside the ear, sound coming from slightly different angles therefore cannot move too far front/rear so a simple single microphone and emiting one inverse wave is going to do a decent job.
The human voice is up to 8Khz, phones allow upto 3400hz, so the wavelength is as short as 0.04M so then you're talking the wavelength is about the same size as the headphone so you'd have to be extremely precise in quickly generating the inverse sound and precise to place that sound. 4cm means 1 to 2 full wavelengths is bouncing inside the ear, so you'd have to be much more precise with sensing the direction of the sound to cancel it. It is possible if you threw enough computational power at it. That power will come eventually, so I expect domestic consumer electronics will steadily improve.
The over-ear headphones have more challenges than in-ear buds for noise cancellation. The sound would have to be sampled from multiple directions and then sent within in the same direction, so a sound wave coming from your front generated one going backwards, etc. The in-ear buds would find it easier but then they get uncomfortable itchy in a long haul flight.