[s_gourichon]

In my opinion, you're spot on: being deprived of hearing the lowest frequencies typically occurs only when there's a pressure imbalance between the inner and outer ear. Therefore, when you experience silence at these lowest frequencies due to noise cancelling, your brain may assume a pressure imbalance must be the cause.

I've had the opportunity to use a variety of noise cancelling headphones over the years, from various brands, both in-ear and over-ear, and they all had this effect.

The good news is that you can become completely accustomed to it: after a while, the brain understands that there's no pressure imbalance, and it becomes a non-issue. Not hearing low frequencies is exactly what we expect from the product.

The article goes further to discuss some slope in a graph around 500Hz, which might be true, but I don't subscribe to that. It seems unnecessary to explain the observed facts and adds nothing.

What is not addressed at all is why all models seem to emit a subtle continuous shhhhhhh across a broad range of high frequencies. It's so subtle that you can only notice it when the outside environment is already quiet. I've never been certain whether it's just noise from the signal processing. My intuition is that it's artificially added to prevent inducing tinnitus in some users.