NB! It seems this console command is not compatible with CS2.
Command Profile

VOICE_SCALE

CS:GO

This command sets the volume of voice communications (i.e. how loud all other players microphones are). Default is 1 (loudest), 0 would mute, 0.5 would be 50% volume.

Syntax
voice_scale [0 - 1]

Description

This command sets the volume of voice communications (i.e. how loud all other players microphones are). Default is 1 (loudest), 0 would mute, 0.5 would be 50% volume.

Syntax And Arguments

voice_scale [0 - 1]
0 - 1 A number between 0 and 1 to repesent how loud the voices of your teammates (or other people using microphones) should be. 0 would be muted, 1 would be loudest, 0.2 would be 20% volume.