Began modeling in hornresp, I started by figuring the throat area at 6 3/4 x 6 3/4 based on the 15" size, relative to 4 1/2 x 4 1/2 for a 10" driver. I set the mouth size for a 30" x 15" horn. I wasn't sure how to set VTC and ATC. ATC I made equal to SD(?) How do you figure VTC? I need a McBean for Dummies book. Thanks, Jerrod