Effects of Boundary Material and Shape on Sound Reflection

I have been using flat, unfinished soft wood boundaries based on Curt Olson's  mic rigs experiments for several years and when I decided to experiment with curved surfaces, I conducted a comparison of quite a few surfaces and shapes and combined them in this video <QuickTime  7mb>. Here's a still image with better details on the spectragraphs < gif 500K)

Note that I used a large diaphragm Rode NT2000 mic placed against the boundaries with the capsules perpendicular to the boundaries. In each test, the clip starts with the mic capsule pointed directly at the pink noise sound source (a speaker 4' away in a deadened studio) so the impending sound waves are parallel to the flat boundaries. While recording, I rotated the mic array 90 degrees  to simulate off-axis sources, paused, and then reversed the rotation back to 0 degrees, the starting point. The spectragrams show quite a few differences that can also be heard by ear.  Based on what I heard in this test and being quite familiar with the sound qualities and imaging of parallel boundary arrays,  I made arrays using 7" hard wood spheres.

After recording with these "perp2sphere" arrays for a year, I have formed some impressions about them which  Mike Rooke has helped me flesh out. Here's a sample recording with two "perp2sphere: arrays used in surround.

I'm happy to discuss what others find/hear in this test of boundary comparisons. Rob D.