The Mason Lounge is Madison WI hosts a jazz night every Tuesday from 9 PM to midnight. It's a very relaxed time and the Mason flaunts a huge selection of craft microbrews on tap. Keystone Light fans will fine their love for swilly beer unrequited.
I play bass with the house jazz group, 5 Points Jazz Collective. Guest musicians are welcome to join, provided everyone knows the same song(s). Horns are always much desired. We have a trombonist and a trumpet, usually. There is also a jazz fiddle player.
The music tends to be low volume and ambient. You can sit closer if you want to critique the musical virtuosity or farther away if you just want to chat, drink beer, and have the jazz in the background. The seating availability is usually quite good early on, so if you want to secure some good seats, arrive early.
It should also be noted that as one of the musicians, I will be a very passive and poor host. But I will be very easy to find, on stage, next to the men's room with a bass guitar. Cheers!