David's Tip of the Day: Band Training, Part 7 - Volume
I've never heard the comment... by anyone... ever... that a band was too quiet. The usual comment is "the band was so loud I couldn't hear myself at all." It's also common to hear from those in the audience, "I think you sounded good, but I couldn't really hear you."
So, our rule of thumb...
While playing on the bandstand, if you're not able to follow the story the soloist is crafting or the tale the vocalist is weaving, you're playing too loud. The vocalist/soloist has to at all times be heard well enough that not only their strong notes come out, but the subtleties as well.
So, at any time you're having trouble hearing the vocals or the soloist, motion to the other musicians to bring the volume down. This doesn't mean to not play with dynamics, it's just to make sure the dynamics are relative to the goal of hearing the who is center stage at the point in the song.