The second compartment is about 8 cm, 10cm including the thickness of the wood. There is a cylindrical hole connecting them. In that cavity, only a hole the size of a wire was made. I will use this section for proper cabeling, and probably use a speakon connector to the back. The top cavity i will place in the 150, fix it from the top, add spacers below to fix it good, and i will make a grill of 4-5 cm to close it off nicely, and this will likely improve venting