Do you have any tips on the best way to soundproof my garden shed for my son to bash away at his new drum kit. I'm not going to any great expense and was looking at using rubber carpet underlay (its both dense and has an uneven surface to obsorb the sound) I thought of fitting ply wood to the interior to creat a cavity & filling it with some sort of soft quilt like material and glue the rubber underlay to the surface of the ply wood, rubber side out.
See the soundproofing projects and contact the sponsors in there, they will be pleased to give you advice.