One thing that particularly impairs my ability to communicate in both local and team voice chat is the low volume of my microphone. My microphone has always been quiet, even with a phantom power supply, even with operating system volume at 100%.
In other applications, there are ways to increase the volume past the level at which it is normally. Some applications and games normalize the volume between all VOIP users and some allow the users manual control over their microphone volume.
In Insurgency: Sandstorm, there is no VOIP normalization and no manual control over voice volumes, one of which I believe should be in the game in order to improve communication.