I'm very sceptical of their claims that ~780Hz is in some way special, especially the way they represent it graphically. Playing a frequency sweep while wearing WH-1000XM3 headphones, I don't notice any particular drop-off there.
Near where I live, heavy goods vehicles are fitted with reversing indicators that make a "cshh cshh cshh" sound i.e. pulsed white-noise. White noise like that is the hardest for ANC to cancel. Sample: https://www.youtube.com/watch?v=A3Wt1_51EVA
Near where I live, heavy goods vehicles are fitted with reversing indicators that make a "cshh cshh cshh" sound i.e. pulsed white-noise. White noise like that is the hardest for ANC to cancel. Sample: https://www.youtube.com/watch?v=A3Wt1_51EVA