snd_surround_speakers
snd_surround_speakers is a console variable available in all 
Source games. Found in each game's options menu under 'Audio', it controls the speaker configuration type to be used for audio outputting. It has four settings, them being:
| Value | Description |
|---|---|
| 0 | Headphones |
| 2 | 2 Speakers (Stereo) |
| 4 | 4 Speakers (Quadraphonic) |
| 5 | 5.1 Surround |
| 7 | 7.1 Surround |
Bug:On system running Windows Vista and later, due to using DirectSound, the game may output only 5.1 surround despite 7.1 selected or 7.1 audio may not work properly without custom dsound.dll (such as one from Creative Alchemy, DSOAL or IndirectSound and using the "snd_legacy_surround 1" command to allow Source to load dsound.dll files). [todo tested in?]
Note:Some Source games (such as 
Alien Swarm, 
Portal 2, 
Counter-Strike: Global Offensive and later games/mods using engine since Alien Swarm engine branch) may not include options to enable 7.1 surround sound without using these console commands.Note:This command is not available in 
Left 4 Dead 2.