help with building a rehearsal room

Hello everyone, my name is Matija and i'm From Zagreb, Republic of Croatia... Unlike most of the people here, i'm not building a studio, but just a rehearsal room in my house where i could practice with my bands. The only thing I need from this rehearsal room is not super acoustics but just sound isolation.. Nothing must come out of this room.. Coz of neighbours, folks that live upstairs and so on.. K, so i sketched up how this space looks now.. the size of the room (without the space where the bathroom is) is: 5,2x4m, thats close to 17x13 feet.. The height of the room is a little more than 8 feet, but as you can see on the pictures, there is a central column going through the center of the room, and the height of the room to that column is 7.7 feet (10cm less). The entrance from the outside is from that door on the left, the windows are wooden, around 6.3 feet in width, and that passage on the right is leading to a room which is exactly same as this one.. That room is used as a workshop... the width of that passage is 4.5 feet.. pics (there is some stuff in here coz the room was used as a storage room for all kinds of crap in my house, but that will be out soon...): So,here are my ideas so far: I was thinking of building a room within a room... The passage to the other room would be closed... The materials, aka the walls of the new room I don't know what would they be for now (drywall?) and I was thinking of stuffing sound isolation material between new and old walls... I wouldn't build the new room exactly how the old room was cos of the wooden windows and wooden entrance door don't really look reliable enough, and it would be nice to have a chill-out zone outside the rehearsal room and a possibility to open the windows in the future and so on... My biggest questions are the ceiling and the floor... I was thinking of using the support column on the ceiling and the 4 inch gap between the column and the actual ceiling to do basically the exact thing like I did with the walls.. Do not let the old room touch the ceiling and stuff the space between with isolation material.. The floor is an enigma to me really :shock: The room is on a ground floor and theres nothing underneath it except the ground, no cellar or anything... So what do you think of all this?