Is anyone able to tell me how come the 4520 twin 15" scoops are described as having a 13' horn length, whilst the 4530 single 15" scoops are only 7' long. They don't appear to be that different in cross-section. Is width a factor? Am I just missing something?

Also, while I'm here: Wouldn't a horn length of approx. 11'6" be more suitable, so as to bring the reverse sound-wave from the scoop back in phase with the direct sound-wave at the 150Hz crossover point between the two (150Hz wavelength at room temp. = approx. 7'8")?

Many thanks for any help that may be offered,
Jonathan Weatherill