True, i also have the impression, that very often players are too quiet and i hardly understand what they say, especially when shooting noises are in the backround.
Although the Voice Receive Volume slider is at 100 % the game is too loud in comparison to spoken voice.
Right now i have 50 % Master Volume and i can only hear those players well, who have their microphone boost on high settings ( microphone setting in windows )
People who are talking in my Teamspeak channel are much louder than people using ingame voice system.
So one solution would be to make the Voice Receive Volume louder with a slider going up to 150 - 200 % or
implement a new slider : Game Volume which reduces only the sounds of the game independent of the voice of other players in the game.
In Insurgency2014 the voice of the players is much louder when i choose the highest setting.
A similar maximum volume would be very nice in sandstorm too.