In part 1 of this post I discussed the ideas behind the hybrid “Tabolin”. The instrument is part violin, part tabla drum and will feature tunable, resonant panels of velum in the body. I hope that the fiddle will have will have playing qualities similar to a Viola d’Amore with its sympathetic strings.
The construction was pretty straight forward, if unusual. I think went down a wrong alley by making long – grain struts to divide the small holes in the upper bouts of the top. They took some long hours to fit, enough time to reflect that even short grain members with vellum glued to the inside would be very resistant to forces pushing from the outside of the fiddle. If I ever make another fiddle like this, I’ll do a test to confirm that theory.
Decorating the outside with the chip carving took a long time but once the decisions about the pattern were made it was comfortably repetitive and engaging work, rather like knitting.
I kept reminding myself that the simpler decorative patterns had worked the best on previous similar projects. I want the violins to suggest organic, natural objects and a simple theme and variations seems to be most effective for this. The theme on this fiddle, because of the holes, was “circles” (as opposed to stripes or polygons which are the other shapes easily rendered with a gouge). I also had the reptilian in mind again and the circles along the center of the instrument started morphing into some sort of overlapping plate shape..
Glueing on the velum took some tries to master. In the first post on this project I discuss why I decided to go with the less practical option of having the vellum on the inside of the plate. One of my fears was realized when I put the completed body into the UV light box to tan the wood. The vellum, which is very hydrophilic, shrank a lot, popped some seams open and the vellum even separated from the top in places. I realized that the velum was trying to relive stress by returning to a flat disk shape, whereas I had it locked into a compound curve shape, like a Pringle.
Method for attaching and tensioning the velum panels.
This strong tendency to shrink is what allowed the velum panels to be stretched tight. This was the method I used, the critical trick was to keep the velum from drying, shrinking and pulling away from the wood, before the bone glue had properly adhered to the wood.
- Cut the velum 8-10mm bigger than the shape of the hole
- Soak the velum in water until soft and pliable (approx. 30 minutes).
- Trace the shape of the hole onto a piece of paper towel and cut out that shape about 4 mm inside the line.
- Use a thick hide or bone glue to adhere the soft velum to the wood.
- Stretch the velum only enough to remove wrinkles. Don’t put any extra tension in the velum at this point as it will tend to creep back as the glue dries, weakening the bond.
- Place the paper towel in the center of the panel and wet it. This keeps the velum from shrinking before the glue is dry.
- Allow the glue to dry slowly indoors, out of direct sun. Re-dampen the paper towel if it is drying out
- Once the glue is dry (4-6 hours), remove the paper towel and the velum will shrink tight in couple of hours.
Tension
The tendency to shrink also has some implications for violinmaking technique. It’s been a general rule in violinmaking, that the parts of the violin should fit together perfectly, without any bending, before being glued together. This makes a lot of sense from a structural, woodworking, point of view. From a tonal point of view, the thought is that the parts will then be relaxed and able to vibrate freely. However adding tension to some parts is a known method for manipulating tone. The best known, some would say “notorious”, example of this is the practice of “springing the bass bar”, which puts tension in the top and tends to promote higher frequency vibrations, making a brighter sounding instrument. (The practice of springing bass bars also seems to have the same effect on the demeanor of non-springing school of violinmakers). Tapering the ribs from the upper corners to top block, has a similar effect of putting tension in the top, but is more acceptable…. because Strad did it.
I’ve often wondered how much tension is acceptable. Working for years on restoring badly distorted old instruments, sooner or later you find yourself forcing the top back onto a body. Usually the instrument will sound fine. I realize that this is not ideal from a mechanical stability point of view, and of course no one knows how good the fiddle would have sounded with no tension built into it, but my general feeling is that tonally the violin is more robust than may be commonly thought and that some tension in the structure is equally likely make a either a positive or a negative contribution to the tonal mix.
The velum-and-frame method of violin construction does feature a lot of inbuilt tension and, aside from the mechanical desire to explode, I’m not sure what the tonal implications are. I guess there will be more higher tones, and a brighter sounding instrument
Pre-stringing tests
I was keen to see whether the drum-skin-and-weight arrangement would work at all so, once the body was complete I attached magnets to the centers of some of the panels. I did get an audible note with some sustain and was able to change the pitch and sustain by varying the weight of the magnets.
In another test I placed a tuning fork on various parts of the body. If I placed the tuning fork on the wood the violin rang, much like a normal instrument, though possibly a little quieter. If I placed the tuning fork on a velum panel the ring was very much quieter, barely audible. This is not very encouraging for my hopes of making a loud resonant instrument, however it may tell something about how violins work.
I think the difference in volume between the wood and the velum may be due to the differences in stiffness of the materials. Just by pressing on the wood and the velum I see a lot more give in the velum, even though it is stretched tight. This may make it a poorer propagator of sound waves. Perhaps if it were stretched really tight the volume would increase. All of this is very curious to me when I think how loud banjos are. I went to a music store and pushed on the head of a banjo and found that it has as much or more give than my velum panels….
Normally when I do something a little new, like the Redwood Violin, where I don’t know what results to expect, I will string the violin up “in the white” and then if I want to make adjustments like removing more wood, or changing the bass bar, it is more easily done. In the case of the Tabolin there is really nothing that I can think of to change if, as is quite possible, it the fiddle doesn’t work. So I decided not to test it before it is completely finished. That way I would be sure not to walk away from the unfinished fiddle if it was a tonal dud. This project is very much about the journey and what can be learned along the way. if the destination should turn to be a disappointment, that doesn’t wholly detract from the experience.
Finishing
I followed a similar method of finishing the Tabolin as in my previous Off-beat Fiddles: A thick application of high-oil varnish, followed by a patina of dry pigments and french polish. I’ll devote a post to this process at point – perhaps when I have a more consistent method. Its all still very exploratory at the moment
