Hi Brian,
A bar gig is a tough one, because some of the people are there to hear the music, and some are there to be at a bar and talk with friends.
So, in my experience anyway, it is always a mixed situation - and not to be taken personally as regards those who are not paying attention.
When you see people who ARE connecting with the music and enjoying in, try to make eye contact, smile, share the sense of mutual enjoyment. That helps keep them engaged.
Also, people LOVE to hear songs they know. It can become almost irresistible to be engaged with the music if you know the song - so your set-list wants to be full of favorites that would suit the particular crowd you are playing for.
You don't want to be too quiet, nor too loud. Again, your audience is mixed - some people are thinking of the band as a performing group, others are thinking of the band as background music.
You want to try to hit the sweet spot that allows people to hear you well, but, you are not making it impossible for some to have a conversation.
Always act as if you are having a lot of fun (even if you might not be having a lot of fun). Fun is contagious, and people will get drawn into your energy. If you are not having fun (yet are still pretending you are), consider the gig to be an excellent opportunity for a full-band rehearsal.
Be well - Lisa