As expected ANC headphones cancel less noise at low frequencies so I guess the 780Hz is a trade off between high enough frequency to be a bell and low enough frequency to get attenuated a little bit less than high frequencies.
The research paper is pretty poor quality and this is mainly a marketing exercise.
https://cdn.skoda-storyboard.com/2026/04/Skoda-DuoBell-Resea...
As expected ANC headphones cancel less noise at low frequencies so I guess the 780Hz is a trade off between high enough frequency to be a bell and low enough frequency to get attenuated a little bit less than high frequencies.
The research paper is pretty poor quality and this is mainly a marketing exercise.