Here’s another soundproofing mistake/myth for you to consider.
Should you, or should you not, attempt to soundproof a room by attaching carpet to the walls?
The answer is a resounding NO. First of all, the carpet won’t make much difference when it comes to the level of sound capable of entering the room. It may help the acoustic absorbency, or the amount of sound the leaves the room, but why would you want to settle for something that only solves 50% of the problem (and, honestly, looks pretty terrible).
The problem you will have with carpet is similar to the problem you will have if you attempt to nail a mattress to your wall. In the end, it’ll deteriorate, look bad, and may even begin to smell bad.
Don’t waste your time on materials that won’t get the job done. Get yourself the right materials and build yourself a sound barrier that will last.