A-did you glue or caulk the 2x4 studs so no air leaks?
B-is the drywall double layer and taped on the seams?
C-is the drywall glued or caulked?
D-What's on the outside wall
E-Personally I would have used double layer drywall, liquid nails and decking screws to build the wall before even trying it out.
Box construction is vital. You may have just made a big bass drum. Also, if it's leaking, that will wreak havoc on the sound and probably leak noise to the rest of the house. This is why most quality in-wall speakers come built into aluminum enclosures. The manufacturers can easily design a speaker if the cabinet is a known source.
B-is the drywall double layer and taped on the seams?
C-is the drywall glued or caulked?
D-What's on the outside wall
E-Personally I would have used double layer drywall, liquid nails and decking screws to build the wall before even trying it out.
Box construction is vital. You may have just made a big bass drum. Also, if it's leaking, that will wreak havoc on the sound and probably leak noise to the rest of the house. This is why most quality in-wall speakers come built into aluminum enclosures. The manufacturers can easily design a speaker if the cabinet is a known source.