Some fields are more recommended to be listened on speaker(s), but again, they work either way.
If you use headphones, keep it at low to medium volume, especially while sleeping, to avoid damaging your ears.
Personally, I already know which audios are louder, so I would avoid these over night; organizing/reviewing your playlist before sleep is the best choice, imo.
Mandalas and Cards are fields, but not offered as audios/not imbued to audios, but to images (although morphic fields are above my knowledge - yes, I can read about them, but they are very advanced stuff).
https://forum.enlightenedstates.com/t/mandalas-mobile-wallpapers/1980