Soundproofing animal noises?

So, I have cats that are very vocal, and my neighbor complained. (I live in a townhouse so I share walls.) What can I do to help muffle the sound of the cats? I am finishing my basement this week and am getting a room for their own and would like to soundproof it. Any suggestions? I have heard the foam squares help, but how many would I need to get and how far apart should they be spaced? Thanks for your help!