Hi ska234

There are some pictures of a Blue carbon fiber harp here, which show the knee.
http://www.blevinsharps.com/index.php?main_page=index&cPath=342

Consider the strings as residing in a vertical plane, at the center of the soundboard.
The strings are attached to "pins", which offsets them from the top "harmonic arm", by a fraction of an inch/cm.
The harmonic arm is (mostly) just a flat board, with various curves cut with say a bandsaw.
The harmonic arm is located on one side of the center plane, except for a part of the knee.
So to finish the knee, add on another block of wood, which begins at the base of the pins, and extends across the center plane,
over to the other side of the sound board structure. Remove parts of this block to match up with the arm, with say arcs, as per PILOU,
(Of course the harmonic arm could be carved out of one piece of wood...)

- Brian