Originally Posted by Bobby Jr
So you've got a two-fold set of requirements: You want to keep sound in as well as making it suitable for those inside drumming.
On the sound treatment for recording/teaching purposes I'd suggest investigating a way to make the drums quieter. I know some other type of drums can be deadened somewhat without ruining the sound too much. Taiki drums - which I've heard many times - are very loud and have a low register for drums (because of their size). That low register is something the sound-proofing would need to consider from the outset.
Typically solid brick/stone/concrete is the only practical way to block low-end sounds. It works better than foam type insulation. In your case you would probably still need a combination of both - to keep the sound in but not make the room unbearable for those drumming. It would need some deadening in the mid and highs and perhaps even a bass trap (google it) in the corner to help keep the sound natural.
Germany has a massive recording industry - one of the biggest in the world thanks to the popularity of electronic music there. I'm certain you could track down someone who could offer advice. I suggest seeking out a sound treatment/insulation products company and ask them. They likely offer some good advice to help potential customers buy the right stuff.
Agree with Bobby. The only way to keep the sound IN the room will be with mass. Thick, heavy walls, carpeted floors, and ceilings with acoustic tiles. Typical sandwich built walls will act like drums themselves.
Once the sound is kept in, then you will also need to adjust the sound properties INSIDE the room. The massive walls, floors and such will often cause echoes within the room that will require some amount of sound deadening. (I think I'd hate to be in there with 9 taiko drummers! I'm already about half deaf.)
One of the bands I played in built a room inside a garage for practice. We built walls of multi-layered sheetrock with the bottom sill resting on rubber hose to prevent any sound leakage from under the wall, a solid ceiling with an addition drop down ceiling with acoustic tiles to kill the sound going upward, carpet on the floors and walls to deaden the sound inside. Outside the garage, you could barely hear anything from inside.
The big drawback was the air inside. It was hot in there. We put a small airconditioner through the wall to help cool and give us fresh air to breathe (that's where some of the sound leaked). MAybe a split-system ductless system would work better? <shrug>