Adding Proximity Voice
This tutorial is going to show how to create a proximity chat for a HL2MP mod or equivalent.
This was implemented in the Source Mod Faceless by Ethereal Entertainment.
Open game/shared/voice_gamemgr.cpp
Then go to around line 228...
bool bProximity = false;
Change that to...
bool bProximity = true;
Next you need to change the distance at which it will project the voice. Locate line 106 and change...
m_iProximityDistance = -1;
To this...
m_iProximityDistance = 10;
Source: http://t-plusplus.com/creating-proximity-chat-in-the-source-engine-sdk/