In total there are 7 overhead/ceiling speakers in the bridge, forming a 7.1 system.
In addition to these as audio input, each station of the bridge has a set of stereo speakers hooked up to it, these are mounted on the wall. And the TV's have their speakers.
For the ceiling speaker set up, refer to the image below.
On the far left, near the conference room, is speaker 1, it uses channel 1.
Speaker 2 uses channel 2.
Speakers 3, there are two of them in front of the elevator, they use channel 3.
Speaker 4, near Robby, is the subwoofer, it picks up the base notes from other channels without needing anything in its own channel.
Speaker 5 uses channel 5.
Speaker 6 uses channel 6.