Noise-cancelling headphones aren't perfect, and if there's a lot of environmental noise, you'll need to do more than put on quiet music. I've been in places wh

Noise-cancelling headphones aren't perfect, and if there's a lot of environmental noise, you'll need to do more than put on quiet music. I've been in places where I wore in-ear phones (they have some passive noise-cancelling effect due to the silicone seal), _and_ with noise-cancelling headphones around those, in attempt to keep the noise out and be able to hear something. Your ears have a sort of physical gain control built in, so if you listen to quiet music the environmental sound (that still gets through the noise-cancelling headphones) will sound louder than if you listen to louder music. I don't recommend actually loud music, as that causes serious damage in the long run. But some modest volume will add some additional masking on top of all the other things done to keep out the environmental sound.