Melani, it depends on the banjo. This weekend I was working on a tune with a friend of mine. He played a mandolin along with my open back banjo. He commented how my banjo was moderate in volume compared to other banjos he has heard. Much has to do with being open back and not having a resonator magnifing the sound.
If you stick a rag or foam in the back of an open back banjo it quiets it down some too. I stick foam in the back of mine, not just as to tone it down but more so that it does not reverberate so much.

Bonnie