[figlio]

I am going to build a room in the roof to use it as a homecinema.I am going to use rockwool slabs on the walls to improve the sound.
If I do all the walls it is better or it will be too much?

[Gary Lightfoot]

I 'converted' my loft into a cinema room, and all I did to tame the echo was cover the screen wall with carpet, and the lower side walls too. It seems to have done the trick.

There was a thread here recently covering exactly what you intend to do, so try the search and see if you can find it. There was info regarding the frequencies the slabs absorbed, so should be useful. They also discussed different mounting and covering ideas too.

Gary.