Logic Pro 9 Bouncing with Logic

I want to bounce a mix for my 22 software synth tracks in Logic. I've frozen all of the tracks thus rendering them to audio.

In order to bounce them all as a single song to an MP 3 (or any other format for that matter) is it necessary to select all of the tracks prior to bouncing or does the BOUNCE function at the output create the new audio file with the sum mix?

Thanks for your help.