Realistic sound doesn't work on planets
Game version 1.192.104 both regular and experimental mode
If you depressurize room on Earth and Mars (probably Alien planet also, didn't test) sound is still transmitted, you can hear speakers, tools, machines without helmet and without touching grid yet it is not even vibration like, sound doesn't change at all.
In space and on the Moon it works as expected (no sound when helmet visor is opened or not touching grid, vibration sounds when touching grid or using tools when helmet visor is closed) my bet is it works on other moons also, but I didn't test it.
Only thing that works on planets is sound muffling when you drop helmet visor everything else seems broken sadly.
Unless sound is transmitted though unvented nitrogen on Earth and carbon dioxide on Mars I have no explanation for this :)