Dulcet

Etymology

From Latin "dulcis" ("sweet"), via a diminutive Old French "doucet." It once described sweet tastes and smells too, but narrowed over time mostly to sound.

adjective · /DUL-sit/
Sweet and soothing, especially of a sound.
What it names
A soft, old-fashioned word for a voice or melody that is pleasant to the ear — often used with a wink of gentle irony.
Example
He introduced the speaker in his most dulcet tones, though the room braced for bad news.
Related idea
Mellifluous also praises sweet sound but stresses a flowing, honeyed smoothness; dulcet is quieter and gentler, more soothing than luscious.