I know there is a protocol for it. Not sure of the specifics of the build of the wall, but it's probably to contribute as little as possible to the FR of the speaker. The test is referred to as π anechoic, where as the normal test is 2π anechoic. That's because pi (π) radians is 180°.
Thanks Chris. It only makes sense that they would test the speaker within it’s specific design parameters. It would still be interesting and IMO useful to see FR graphs of the various in/on wall designs.