|Marx Unverdorben, Fenton house, London|
The next two examples are from a little known Hans Frei at the Met in New York and a Pietro Railich theorbo in Brussels.
This the only photo that I have showing the size of the apron relative to the width of the bowl. The inside apron measures 32 cm long, 29 mm deep but only 4 mm thick at its maximum. It tapers to 1 mm at the ends. The bowl is 31.6 cm wide. It is noteworthy that this inside apron is sculpted from 4 mm at the top surface that glues to the belly to 1 mm at the bottom along its entire length.
This photo shows the inside rear of the bowl of a lute by Laux Maler that until recently was held privately and unknown to the lute community. It had been converted into a lute-guitar as was the fashion in the 19th century and while being restored to a more original configuration the restorer discovered the original Maler label under added paper reinforcement. The lute was subsequently purchased by the Musee de la musique, Paris. If you look closely, the remains of the inside apron are visible but only as a half circle nub of wood. The original apron had been truncated into a style typical for guitars. Since it was being rebuilt into a guitar, custom dictated that it should have an end block. Somehow, changing this construction feature was an essential part of creating the "guitar" sound. I taught instrument making for many years and one of my students built a lute-guitar. Although it had many guitar-like features besides an end block, my student remarked disappointedly when he finished:"It doesn't sound like a lute, it sounds like a guitar."
It seems to me, from the examples that I have seen and the experimentation that I have done, that there are benefits to providing a firm gluing surface along the rear edge of the belly not just for structural stability but for acoustical stability. By that I mean the ability to control, by the length, breadth or depth of the inside apron, the vibration of the bridge and belly in this very critical area in order to achieve an extra degree of resonance, clarity or sonority. Removing a portion of the wood from the inside apron by sculpting from top to bottom, as indicated in several examples, demonstrates the principle of maintaining strength but reducing mass which is really what historical lute building is all about.
My Kaiser inside apron measures 27 cm long, 35mm deep and 6.5 mm thick tapered to 1 mm at the ends and bottom. The bowl is 38 cm wide.