As you know, I am not a builder (though I am a documenter of banjos), but I do play early banjo music. With this, I have a strong tendency to perpetually tinker with setup (bridges, nuts, strings, and head tension), usually making things worse. Yet, I don't give up. I do this because I am working to get the ideal sound from my mind's ear onto the instrument. After many years of tinkering with early banjo music and my reproduction instruments, I finally feel like I am onto something that aligns with my aural vision and reflects my personal tastes. I thought I'd share what I've learned (though others have probably come to these conclusions and I will demonstrate my skills as Master of the Obvious).
Well, I feel as though I have established very good consistent head tension on my Hartel Ashborn. I took off the wonderful rosewood nut Jim built (so I wouldn't screw it up) and replaced it with a piece of scrap. With this scrap I have filed grooves so that the strings are literally resting a paper's thickness above the fingerboard.
From there, I took one of the bridges that George Wunderlich built for me (an incredibly dense, but extraordinarily light piece of maple, I believe) and, with my trusty piece of sandpaper, sanded the bridge thickness so that it is quite thin at the top (as thick as a quarter) and increasingly thick towards the feet (I'm not at home or I'd measure it exactly and report the measurements at the feet and the top). THEN, and this is where it gets meaningful for me, I began slowly sanding down the bridge height.
Every 5-7 careful swipes of the sandpaper, incrementally shortening the height of the bridge, I replaced the bridge to its 28 inch scale length position on the head of the banjo (which is tuned dGDF#A). Then at the 10th and 12th position on the first string, I began to press the string down, NOT to the fingerboard, but to the point where I could hear the overtone series of the note, usually just above the fingerboard. I identified this point as the most important point of responsiveness when pressing down the string. From here, I continued to incrementally sand down the height of the bridge until the slightly depressed string, my desired perception of the overtone series (what I call "the point of greatest responsiveness"), and the fingerboard met at a single junction.
I must say that I am REALLY pleased with how things are coming together. For example, reaching the 12th-15th positions, where some of this early banjo repertoire goes, is much more forgiving. At first I was concerned with the bridge being too short and my finger and thumb annoyingly hitting the head of the banjo. HOWEVER, I feel as though, since I've maximized the sweet spot of each semitone on the fingerboard, I don't have to hit it as hard and am, thus, improving my own economy of motion.
I'll keep monitoring these results to see if my claims are warranted. Ultimately, I feel as though I have experientially come to appreciate a deeper perspective with the early banjo (and banjo setup, in general) and wanted to share my enthusiasm (however parochial my insight may actually be to those who are builders and have a stronger grasp of the physics of sound).
Best to you all,