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Yes, the Mantaray CD horns have a much flatter power response over a wider arc than the antiquated rising on axis expo horns.

Right, all else equal, a 15" trumps a 12", so use two 12" to 'have your cake and eat it too'.

A 15" is beaming at 90 deg around 900-1000 Hz depending on its design, so for me this is its XO limit. For a 12", it's around 1350-1500 Hz, so as good as it may sound to some, the M19's ~1200 Hz XO is a 'make do' design to my way of thinking; but it's pretty obvious the designer(s) were given a tight budget, so all things considered, it's an excellent design. A pity they weren't allowed to switch to a Mantaray when the 416-8C was swapped in and drop the XO point.

I tried, Dick (Richard C., a local to me) drew up the stocker for both the M14 and M15 as well as his modded designs with the latter measuring more M19 like IIRC and posted it all on his web page.

GM