Way 1 · best default
Would you mind turning it down a bit?
Polite and clear. "A bit" makes it a small favour, so it's easy to say yes to.
Examples
Sorry to bother you. Would you mind turning it down a bit? I've got work early.
Hi, would you mind turning it down a bit? My son's trying to sleep.
In a conversation
A: Hi! Everything all right?
B: Sorry to bother you this late. Would you mind turning it down a bit, please?
Common mistake
Not: Your music is very noisy. Please reduce the volume.
Say: Would you mind turning it down a bit?
"Reduce the volume" sounds like a sign on a wall. "Turn it down" is what people actually say.
