Sunday, September 14, 2008
Assymetrical Oud Bowls
Finishing the construction of an oud bowl is a milestone. For me, the bowl is the most technically demanding aspect of oud construction. After my second instrument I decided that I wanted to duplicate the bowl shape of older ouds, specifically the shape most commonly used by the Nahat dyanasty of luthiers. My first two bowls were symmetrically shaped. In other words, I took half of the face profile and rotated it 180 degrees around the centerline of the face. Theoretically, this meant that each rib was exactly the same size and shape.
Like slicing a perfect orange in half, then separating the sections. All the sections would be identical.
My second oud had a symmetrical shape. The bowl profile at the apex was taken directly from the face profile.
The shape of Nahat bowls have two distinct differences over symmetrical bowls. The first is the shape of the tail end. It doesn't terminate (meet the face) at the apex of the curve, but rather continues back a bit past the apex to meet the face at a greater than 90 degree angle. This makes for a more aesthetically pleasing look, and more importantly it softens the bottom corner of the face.
This makes the oud more comfortable to hold, as the players arm curves around the bottom of the bowl.
The other difference occurs towards the neck end of the bowl, at the apex of the bowl. The bowl is made deeper in this area. This also gives the bowl a nicely curved shape, but the real effect here is the increase of the air volume of the bowl, and combined with the position of the deeper section itself (which is directly behind the main soundhole) the projection (volume) of the oud is increased. The greater air volume probably affects the openess and fullness of the sound as well.
There have been a lot comparisons between the shape of the oud and the shape of the human body. The closest natural shape I've found that mimics the Nahat shape is actually a kalamata olive. Can you spot the oud in the following picture?
Departing from a symmetrical shape presents all kinds of challenges. Each rib is now a different shape, and with the curved tail end, the ribs closer to the face must twist at each end. No longer is the rib simply bent in one plane, but it is now a bent and twisted rib. In order for the ribs to join at their edges seamlessly, one must accurately accomplish three tasks. 1. Bend and twist the rib to match the profile of the bowl (while matching as closely as possible the curve of the previous rib) and land flatly on the the tail end and neck end gluing blocks. 2. Joint the curved and twisted rib to the previous rib (I shoot for a light-tight joint) without altering the way the rib lands on the mould. 3. Joint the opposite edge of the rib in preparation for the next rib. For me, this involves a stepped approach of gradually tweaking the bend and twist of a square-sectioned rib until I'm close, sawing the taper in one side, jointing the edge on an inverted jointer plane, further tweaking the bend and twist, final fitting of the edge, and finally, sawing and jointing the opposite edge.
Sometimes during this process, the taper of the rib itself will be off, causing the widest part of the rib to depart from the mould, instead of hugging the shape. More material must be removed from the ends of the rib in order to pivot the rib into correct position. Of course, this can drastically change the twist of the rib, which must then be corrected on the hot bending iron.
If the rib continues to need twisting, I'll heat the rib in the area I want to twist, place the rib on the mould, then gently but firmly twist the rib by hand while it's still pliable. Alternating jointing the edge and bending/twisting is necessary to avoid overcompensation of either tasks. I prefer to fit all ribs with oversized (by at least 1cm) square sectioned blanks in order to leave the most room for fitting. On good days, I can fit a rib in a little over an hour. On bad days, I just chuck the problematic rib across the shop and call it a day.
When things go well, I end up with a bowl of the intended shape and size, and a feeling of relief after accomplishing the most difficult part of oud construction. My latest oud bowl is taken directly from the shape of the old Nahats.