I think the print bed size of most hobbyist 3 printers is no bigger than 8in x 8in, so that would be a slow job to make 16 squares which would then be glued together to form the horn. Each square taking 10hrs. But conceptually, if one had a printer that could handle a full 28in x 28in it would be relatively easy as the modeling would be simple given the PDF file. One could just overlay the image and manually do a spline curve fit, then extrude. You could make the smaller 20in one as a 3x3 or 9 and that would be faster.
