Acoustics and soundproofing is not the same. Soundproof is referred to as isolation and is about stopping sound coming in and out of the studio. Acoustics is about stopping sound bouncing around the inside of the studio (reverb). For example, when you speak or sing in the bathroom, that echo is reverb. All rooms have reverb. For recording vocals and mixing, you want minimal reverb. For live instruments, controlling the reverb but still keeping some reverb is often better.