Thanks! I rope caulked the horns of my Heresy IV in an effort to reduce a bit of resonance or sibilance and subjectively it seems to have worked. After caulking I played many of the songs that had some kind of sibilance (James Taylor, Norah Jones, Ella Fitzgerald, etc.) and it no longer bothers me. I'm glad you were able to measure a difference but looking at your charts makes me wonder if the green and red are mixed up? I hear less treble energy after caulking the horns. Regardless, I prefer the sound and seeing a difference in the measurements makes sense. Many thanks for sharing.