All measurements taken with a radioshack SPL meter through room eq wizard. Levels not calibrated for volume, only relative performance.
The first pic shows a ground plane measurement of the horn with 1 vs 2 drivers connected. I wanted to see if the FR trend would change when the second driver was added.... the passband of interest didn't- it only got louder.
The second pic shows the response of the raw Eminence Alpha 6 divers, measured while held in my hand, close mic'ed at about 1 inch. At first, I couldn't figure out that dip at 630hz in the first pic- I thought it was related to some diffraction or high order mode cancellation within the horn. Turns out it was just the drivers... whew! Hopefully, I can tame that with little EQ.
The third pic shows how the top end of the FR got pushed out to around 900hz after routing the frustrums into the ports. I used a plunge router with a chamfer bit after drilling 5/8" holes. This is compared to the first ground plane measurement with no frustrums.
The fourth pic shows a bump in the low end of the FR after sealing the back of both drivers with blue masking tape- It acutally worked! However, the volume is too low for what I want, making the boost too high with too much roll off below. I'll need to seal the drivers in PVC or wood boxes. Interestingly, the top end of the FR got pushed out a bit as well- didn't count on that one.
Also, note that plugging the <1 inch hole back of the horn where the CD will mount really didn't affect measurements much- can't explain that one.