These are worth every penny, especially when starting a credible business ;
http://www.ecophon.co.uk/
Cost in Finland around 100Eur/6sq.m, you may find it cheaper locally. They also sell fancy ways to support the acoustic plates in place but there is clearly way to save by just gluing or screwing the material in place, it works fine like that. For recording studio almost all large surfaces need to be covered either to make them sound diffusing or absorbing, so you want to avoid acoustic "mirrors" which would reflect the sound creating echo.
But even before acoustic material the studio dimensions and structures should be matched for proper avoidance of standing waves and sound proofing by structural isolation not to transmit mechanical vibration sound is.
At home there is no need to be so pedantic, I've got two facing walls and ceiling covered with 5cm ecophon basic grey plates in my "media" room (extra bedroom originally). Third wall (listening end) is intentionally "hard" material namely plywood "Wisa Decor" and fourth is bookshelf with books and magazines which are also excellent sound absorbant, floor is covered with thick fabric mat. This arrangement is sometimes called; dead end - live end.
On the wall install the acoustic plates are just glued on the wall but on ceiling I wanted different look and some sound diffusion capability, so there is blue fabric and 1cm narrow pine slats with varying spacing on top of the plates.
By this arrangement I have enough sound damping in there but still good amount of reflected and diffused sound to make acoustic instruments sound lively.
The room is mainly used as intrument playing space (flute and piano), possible to close soundproof door to the house, not to drive everybody crazy when practising and secondarily room serves as home theater. With nice soft sofa, 5.1 sound and projector. Works pretty nicely ;-)
