What defines a boundary?

When you place a subwoofer in a corner you get more spl.

So what defines that corner?

A concrete floor does the job, but what about walls? 2x4 framing and 1/2 inch drywall seems to work. A bed sheet hanging from the ceiling wouldn't work. At some point in between is where the surface begins to act as a boundary.
 
Thansk, but I'm not really worried about curtains. I'm interested in defining what actually makes a wall a wall, when it comes to bass frequencies. It doesn't take much to reflect higher frequencies and that is a whole other can of worms. For bass, it takes more mass and surface area, but how much is the question.
 
For bass, it takes more mass and surface area, but how much is the question.
This thread might give some insight as to surface area:

Horn Extender/Wave-guide for TH

My experience with boundary walls is like in speaker cabinet construction, mass is not as important as stiffness. All the "barn doors" or "wave guides" in the above were 1/2" (12mm) plywood with minimal bracing.
A thinner "wall" of 1/4" (6mm) plywood if not well braced will be diaphragmatic, vibrating at various frequencies which may result in cancellation rather than gain.

Examples like this :

https://www.pfsteco.com/techtips/pdf/tt_plywooddesigncapacities
https://www.fpl.fs.fed.us/documnts/fplrn/fplrn059a.pdf

Give insight regarding bending stiffness of various thickness of plywood.

Art
 
Thanks Art. Lots of content there to digest.


I hadn't even considered using the subwoofer waveguide approach. That could allow a subwoofer to be placed out into the middle of a room while still gaining a few db of boundary gain, if I'm understanding this correctly.