If you want to be quiet and not scary, you can consider: sadness or happiness, the theme music of BBK, the prelude to the undead in Warcraft, the great compassion mantra and so on.

If the elderly like nature, they can consider: forest rhapsody, bird singing in Motorola's built-in music and so on.

Old people's ears are not very good. If they want to speak louder, they can consider: believing in their own prelude, unforgettable injury, and so on.