I spent most of my Tuesday -- selfishly -- building this thing. Fortunately, it turned-out much more wildly-successful than I could have ever imagined. It combines one of my obsessions -- a cello/guitar-scale, 2-sting, fretted neck -- with my general banjo-rim obsession -- and merges it yet again with a high school sweetness for the sound of Mongolian and Tuvan "horse fiddles." When I realized that the older variants of these used skin heads instead of wood tops (which only makes sense for a place devoid of trees in the normal sense), I knew gorgeous, cello-like low tones must be able to be produced from a weirdo, banjo-rimmed, bowed instrument.
Anyhow, I'm calling this class of instrument banjello for the moment. In construction it's similar to some variations of old minstrel banjos with a neck that, in one piece, runs from the headstock and through the rim so it serves as a "dowel" in the rim as well (and is thus supporting tension through its entire length). After that the banjo comparisons depart as the neck angle is canted-back like a bowed instrument, the bridge is tall like on a bowed instrument, and there's a cedar soundpost that connects the head (directly next to the bridge) with a 1/32"-thick plywood "resonator" attached to the back. This resonator serves like the back on a bowed instrument -- but moreso as it's so flexible -- turning it into a full-on secondary soundboard.
The scale length is 24 3/4" (borrowed from a Gibson guitar) and I have both a zero fret and a "spacer fret" (or nut) on it. I used the two low strings from a perlon/nylon-core (as opposed to higher-tension steel-core) set of cello strings and have them tuned-up a full step above the low notes on a cello -- to DA low to high (this is the same as a guitar's two lowest notes in drop-D tuning). When I first put this together I had no idea what to expect, but after tweaking the design to optimize the tone via the resonator and whatnot, it's turned-out to be very powerful for its size.
Volume is comparable to average 3/4 cellos I've had the chance to work on and play and the tone is similar, too, though a bit huskier and airier -- and even more fundamental, believe it or not. It has the same bass response, too, which made me super happy. I expected throaty, but not full. I've been playing it with a 1/4-size German-style double bass bow as I prefer underhand grip on a bow (just like viol players). The perfect bowing spot on this is right at the join between the neck and the rim -- which is where I planned for it to be.
The rim is a 14" Remo "buffalo drum" frame drum (with their Acousticon shell -- meaning multi-ply cardboard, basically, pressed really tight) and sports a pre-tensioned FiberSkyn head. I chose it for its looks (the white canvas material glued to the exterior of the rim works with my natural maple neck) and also because FiberSkyn has two attributes that are desirable for a bowed instrument of this nature -- it's thicker, more fundamental in tone, and mellower overall vs. other Remo head materials.
I've used Remo tar drums in the past for banjo bass adventures and I can safely say that these frame drum rims are quite the catch for folks wanting to experiment with oversize-rim banjo-style instruments. They sound excellent, are extremely durable, and don't require any heavy hardware to keep the heads snug.
Quite a bit of time on Tuesday was spent just planning the neck cut to get the angle and design right to match the rim's design and the needs of the back-angle on the neck with as little modification effort as possible. I made a pattern of the neck as I went, too, so I can make another one of these on the quick in the future.
The maple neck is pretty thin at just 7/8" across, but it's perfectly suited to its two-string role. I poke through my local builder's supply store from time to time and pick out flatsawn planks of maple that happen to have been cut directly on the quarter -- and then stash them for later. This quartersawn stock, once dried-out for a while, makes a very, very sturdy and stable neck -- especially when laminated for guitar neck widths. Sorting through regular maple supplies like that also afford me long boards to make these neck-through instruments with, as regular luthier-supply wood usually terminates at 35" or so.
Note that I've used lightweight Hipshot tuners to mimic the big pegs on those world "folk fiddles."
The neck is cut in a deep U-shape that I've always liked on tamburitza-family instruments and some Greek bouzoukis. In general, I prefer a deeper neck as the fretboard width gets narrower. The frets are jumbo stock and, as you can see, I haven't added side dots yet -- but I will.
I've found that 3/32" is the height the action wants to be at the 12th fret to keep the strings from rattling on the frets with the attack of the bow. It feels pretty easy on the fingers, anyhow, since the strings are nylon-core -- though the player has to be very aware that the strings have to be pressed-down right behind the fret for best tone.
Because I wanted a darker tone, I used rosewood for the bridge. Obviously, I haven't bothered to refine the look of it much, either.
A bit of foam mutes the string afterlength. I've noticed the same thing being done with features and leather on folk instruments from Asia. My younger daughter wants me to stick a big bunch of feathers in. We'll see!
Here you can see that unbraced, extra-lightweight "resonator" back and how it's held-on with an assortment of tiny screws.
At this angle you can see the "sound port" and how the bottom of the neck/dowel pushes-up this section of the "resonator" plate. This points directly at the ear, for one thing, and affords the hands access for easy placement of the soundpost, for another! Because the back plate is "warped" over that bottom bit of the neck/heel, too, it makes the back a little more stable as it becomes "arched."
Here's my soundpost -- a bit of tight-grain cedar guitar soundboard material. I didn't want a stiff, round post like in a violin as I figured it'd damp the head too much. This more-flexible flat piece of cedar sounded best of the various options I tried (about a dozen different shapes, weights, and woods).
The rope on the buffalo drum rim seems to serve no purpose except to provide a grip for a drum player, but I left it intact anyhow. It adds to the folksy charm, I think.
There's only one screw near the "tailpiece" end of the instrument that actually locks the neck into the rim. This side is simply slotted firmly into a small cut that I made in the rim and in the dowel/neck itself.
Here you can see the soundport. Please excuse somewhat non-final sanding on the heel -- this was built as a proof-of-concept rather than a beauty.
I forgot to take a picture of where the strings come out -- but they're actually just popping out of two holes drilled in the rim. I'll have to change that to a small tailpiece-holder, later, as my original design had more access to the interior of the rim on that side!