Free open mic nights, giving up-and-coming Illawarra talent a relaxed environment to play without the pressures of a paying crowd, are popping up all over the CBD, bringing sound and energy to a city thirsty for music.

Local performer Rhea Mangles will launch her new hip-hop open mic night on Wednesday, hoping to turn Three Chimneys into a local hub for urban music.

"Nights like this are popping up, which is a good thing because it lets people see talent they wouldn't necessarily see at bigger places on bigger nights," she said.

"You discover hidden gems and meet people to work together. I met my business partner at an open mic night."

To run weekly, the nights will have a booked headliner but the bulk of the evening will be given over to open mic artists to show off their performing chops.

Sean Harlor runs a night with a twist each Thursday at Howlin Wolf. His band, Oxford Groove, plays jazz classics as the "house band", but pass their instruments to anyone wanting to get up on stage for an open jam session. Each night since January there has been a capacity crowd.

"It's a different environment, less competitive. People play to have fun rather than show how good they are," Mr Harlor said.

"People from Sydney come regularly, even just to sing one song. There's a lot of good musicians here."

Mr Harlor said the nights presented a unique opportunity for collaboration between musicians who might never otherwise meet.

Anna Chaplin's nights at Red Square have the same aim, with the cosy Wednesday nights a haven for mellow acoustic artists.

"It starts a ripple effect. Someone might do their first gig one week, and the owner could book them for a paid gig the next week," she said.

Ms Chaplin said with a lack of CBD venues suitable for full band concerts, open mic nights were a way for music lovers to get their regular fix.