That depends on what you use to communicate (ingame voice, skype, TS3 etc).
Generally OBS takes what ever you set as audio output at the same volume what you set in windows for that device, if you keep it at 100% in OBS.
If you wanna raise the volume, you have to increase the output volume in the software, before it hits the windows internal mixer.
As the last solution i would say - increase the desktop boost from 1 to 2, that will double the volume. Be careful, that can add distortion, but this can help. Try this as the last solution, i would rather switch to something like TS3 (where you can adust the volume of each person and the main volume) before overdriving the boost in OBS. Specially because its hard to balance and loud sources will cause distortion and twitch chat will spam "RIP ears" :-)
