To make the curved part of the horn flare bend a piece of 3 mm plywood around some battens that have been glued and screwed to the side walls to form the curve, then glue and nail another piece of 3mm plywood on top of the first piece. Keep doing this with another 4 pieces of 3 mm plywood until you have all 6 pieces glued and nailed together. The finished curve should now be 18 mm thick. For a better job use 4 pieces of 18 mm ply to make the curved former. Use a jigsaw to cutout the curve from the 18 mm ply and glue and screw them in place evenly spaced across the width of the curve. The 2 outer most formers should be positioned right against the cabinet walls.
I don't like scoop bins (for an explanation see the FAQ's page) , but if you must use them then the Super Scooper works better than the rest
You must use a high pass filter set to around 30 Hz with scoop bins as the driver becomes unloaded below this frequency