Poker room, only sharing 2 walls?

[Pokerguy]

I have moved into an apartment and want to turn a back room into a poker room. Obviously its too loud.  I only share two walls with other apartments. we live on the top apartment and below us is not a problem either, so do i need to soundproof all the walls or just the two that i have in common with other apartments? 

Also what is the best value for money remedy for my situation, it will mainly have to insulate against voices and maybe a bit of music, but voices is my main concern.