This is an acoustic lens designed to be placed in front of a midrange or tweeter speaker driver. It spreads the sound more evenly in the room eliminating most of the on-axis beaming effect. It does this by reshaping the planar wave front into a spherical one. I published a paper with the details here:
I have uploaded both round and square flange versions. You can scale them and drill holes as needed to fit your driver. These were designed for the Beyma 10" 10MCF400Nd midrange driver and Beyma TPL-150-H tweeter. These are a challenge to print. It took my Lulzbot printer almost two weeks to print one lens. I recommend using a low-warp version of ABS which worked better for me. Slic3r takes forever to process the STL file. You might want to try the speedier Simplify3D product. FreeCAD can be used to view the STL file. The algorithm that created the STL file is in the paper above.