// The idea is to twist a translated circle:
         // -
         /*
          linear_extrude(height = 10, twist = 360, scale = 0)
         translate([1,0])
         circle(r = 1);
         */

         module horn(height = 10, radius = 6, 
         twist = 720, $fn = 50) 
         {
         // A centered circle translated by 1xR and 
         // twisted by 360° degrees, covers a 2x(2xR) space.
         // -
         radius = radius/4;
         // De-translate.
         // -
         translate([-radius,0])
         // The actual code.
         // -
         linear_extrude(height = height, twist = twist, 
         scale=0, $fn = $fn)
         translate([radius,0])
         circle(r=radius);
         }

         translate([3,0])
         mirror()
         horn();

         translate([-3,0])
         horn();