Test video. Heil is fed pink noise from the Behringer through a 13.3 mfd cap and in series with a 4-ohm Mills 12.5 watt resistor. This creates a high pass Butterworth filter at ~1,500 Hz.
Next step is to make a 30 degree from acrylic rod. The wider wedges didn't seem to work as well as the smaller, but I only tried a couple at this point.
Mic is on-axis at 2 meters.
Voila:
https://youtu.be/o8Ftyl303Gk
Edit, I guess they don't make acrylic rod in that angle. I guess I could try to bend some metal, but it won't have the same finesse.