play --show-progress -c 2 --null synth 01:00 brownnoise \
    reverb 19 vol 0dB bass 6 treble -3 repeat 558

Adjust bass and treble to match your headphones.

It sounds like a big waterfall, or like a continuous wave crash. And it's stereo. :)

EDIT: Or this:

    play --show-progress -c 2 --null synth brownnoise \
    reverb bass 6 treble -3 echos 0.8 0.9 1000 0.3 1800 0.25

The one with echos is a bit softer and more natural-sounding.