I am interested to learn more about the method Don Keele used in the 70s when triple stacking horns like the HR9040. The central horn fired forward and ran full range with EQ to 20 KHz while the upper and lower horns of the triple stack were somewhat tilted toward the central horn of the stack and were both allowed to naturally roll off. This was intended to deal with any comb filtering. Has anyone got any reference links or image links to one of these stacks. They were very large and I cannot imagine ever forgetting seeing such a stack. Thank you for any assistance. Best regards Moray James.