I build this myself because the standard solutions were to high and expensive.
The acoustic is great and i can go on all night long without trouble with the neighbors.

It cost me 5000 euro to build it.

An note is that between every layer of wood there must be a layer of soft isolating (the green stuff) material.
Otherwise the wood could make noises with the low vibrations.
The bottom of the frames are on rubber foots from 2,5 cm.
Because
of the isolation material (WOLF tristar) i have chosen the walls are
not more as 8 cm inside the frame. The sound reduction outside is 97%
with the door closed.
I first build the frame and them layered to the inside.

First layer: Soft (green isolation)
Second layer: Soft pressed wood.
Third layer: Wolf Tristar Isolation with paper and silicium.
Fourth layer: Soft pressed wood.
Fifth layer: Soft (green isolation)

Sixth layer: Medium wood stripes.

Its complete destructible