just for snits & giggles.
first off,I made 5" ones for testing and still need to do 3" & 4" because I believe there's a drastic difference between 3" & 5".
the hi-eq is also a bit exaggerated so the point gets across better.
what I used,available @ just about any craft store or even (gasp)Walmart.
attached to the blockers & grill w/ 2" industrial velcro tape.
not too visible from a distance but if I did them in circles you wouldn't be able to tell @ all-
clip one- stock speaker close mic'd on-axis w/ an AKG D8000s (SM 58 clone)
clip 2- beamblocker close mic'd on-axis
clip 3-mic back 2 ft. on-axis
https://soundcloud.com/rlc-ltd/diy-beamblocker-experiment
clip #3 doesn't sound that great to me but I'll redo it w/ a condenser mic back about 3 ft. then do it again w/ all four blockers on (I only did 2 for now).