The Steel-string Harp Guitar
Excerpted from "Sixty Years of Listening to Wood Sing," by Michael O'Brien, 2019.
Introduction by Gregg Miner
The goal here was to create something more graceful than the traditional Dyer/Knutson models. So I made the bass arm slimmer, blended it into a Florentine cutaway with a single, sweeping curve, and slightly reduced the lower bout. I also outlined the basic guitar shape with a two-piece top.
A Dyer "Symphony" Harp Guitar, Steel-string Harp Guitar,
made by the Larson Brothers, 1907 Michael O'Brien, 2019
Acoustically, I was looking for a sound that would enable a fairly unified melody played over several strings and across different areas of the fretboard — but with the sustaining characteristics of a traditional steel-string guitar. If the right balance could be achieved, and the bass resonance could ring without becoming boomy or muddy, this mix should be possible. I think the instrument comes very close to that.
The guitar has an elevated, multi-scale fingerboard, a side port, six sub-basses, a single bridge with separate saddles for the mains and subs and plenty of room at the headstocks. The back is on the horizontal plane, but like many guitars with elevated fingerboards the top of the instrument tapers away from the heel.
Since it was to be mine, the string band and neck profile is that of a classical guitar (50mm wide at the nut, but with a 20” radius). This is almost non-existent on steel-string instruments, but it fits the way I play. If this instrument were to be for another player, with a different technique or playing style, these details would change.
The scaling also fits my hand: 25.4” (a fairly standard steel-string scale) for e’ and 660mm for E (same as a long-scale classical guitar), with fret 5 perpendicular to the center line. This makes the upper positions easy to reach with only a mild extension required in first or second position.
The sides and back are quilted Eastern Cherry. The top is Alpine Spruce. The bindings and bridge are Bloodwood; and the neck is Black Walnut. The Fingerboard is Rocklite, which is a wonderfully acceptable alternative to the Ebonies.
These are sustainable species, not listed in the CITES appendices. Working as environmentally responsible as possibly is important to me. Given the present conditions of tropical forests world-wide, I find it hard to ethically justify using the rosewoods, ebonies or similar species, despite their beauty and acoustic properties. In fact, I have turned down commissions from players who have insisted on these. (Confession: I do have a classical guitar in East Indian Rosewood which I began a few years ago and which I will finish. Also, the bridge and bindings of the nylon-string harp guitar—below—are East Indian Rosewood. Even though I still have some more small pieces in my shop, I’m done with it.)
The top bracing is a modified, symmetrical X-brace pattern (to allow for the multi-scale bridge position), and the back is a modified radial pattern (to accommodate the sub bass arm). The top pattern tends to balance the two halves of the long dipole while creating many smaller areas, more or less proportional to each other, for overtones and higher frequencies. That’s the theory at least. At this point in my career, I am able to trust my ear as much — if not more — than theory. A guitar body amplifies the strings in so many, complex ways, that, for me at least, I let my instincts and ear guide me most of the time.
The back bracing pattern tends to favor the large monopole, and thus the lower fundamentals. Again, to me, this just seems appropriate for a harp guitar and for the sound ideal that I’m going for. I did not intend this guitar to be played with the back dampened on the player’s torso. I tend toward a classical way of playing, keeping the back free to vibrate. It’s just personal taste.
THE “FLYING BUTTRESS” BRACE
A long brace which is parallel to the sub-bass strings spans the entire length of the guitar. It runs from the sub-bass headstock to the heel block without touching anything along the way. Its purpose is mainly structural. However, it is free to vibrate, thus minimizing any dampening effect it might have. It’s a piece of quartered, straight-grained ash, wider at the ends and middle. The joint at the heel block is reinforced with a second, small piece, and let into a small mortice. The extra mass in the middle creates a kind of pendulum effect and encourages the brace to vibrate. One can easily feel this through the side port.
The principle is something I borrowed from the late 17th-century and early 18th-century pianoforte designs of Bartolomeo Cristofori (on whom I wrote my dissertation — and also the bio for the New Grove Dictionary). One of Cristofori’s great innovations was to separate the stress-bearing components from sound-production. It is a principle still used by modern pianos. In a different way I’ve also used this principle on a six string guitar, which has a kind of “flying” x-brace on the back.
Also, the harp guitar’s upper transverse brace is not only let into the linings, it is fixed permanently to the back of the neck block. It does not contact the sound board in key areas, mimicking Jeffery Elliott’s open harmonic bars, found on many of today’s classical guitars.
A joint in the top is inherently weak, particularly a cross-grained joint like this one. But it’s necessary for highlighting the basic guitar shape. So, the joint is reinforced with a spruce patch and a small brace. Since the bass arm’s liners are nearby anyway the overall loss of strength is negligible. A thin strip of black purfling adds visual refinement.
The side port is reinforced from behind with a patch and is bound. By adding a second sound hole, the boomy-ness can be reduced, for basically the greater area of the sound hole, the less boomy the sound.
THE CURVE INTO THE CUTAWAY
In early designs I had considered adding a layer of carbon fiber to the curved side that extends from the bass arm across the neck joint into the Florentine cutaway, but ultimately chose to laminate it. I used a three-layer lamination, pre-bending each layer and glueing it all up with a structural laminating cement which is hard and has virtually no creep.
A CARVED SCOTIA
I’ve often thought the back of the sub-bass headstock on harp guitars was an awkward design spot. It’s usually handled in a simple, utilitarian way. So I added a Scotia profile carved directly into the block. A nice detail.
Incorporating a single curve from the sub bass arm into the Florentine cutaway requires re-designing the traditional neck joint. I used a mortice and tenon joint within the perimeter of the guitar. Obviously it must be precisely aligned, which is tricky. I used this joint effectively on a six-string prototype, which has since been sold. The Harp guitar’s neck is otherwise a simple bolt-on with wood-to-wood contact.
ROSETTE AND OTHER INLAY
Rosettes and inlays are personal touches. Here are some photos of the rosette and the thin maple lines inlaid into the bass headstock.
After scoring a line with a scalpel, I then shaped it into a rectangular groove with a knife made into a small scraper. So the groove fits a strip of veneer which is inserted into it, glued and trimmed flush.
Although I have repaired vintage guitars that require nitrocellulose lacquer, I prefer a well-executed, traditional French Polish on new instruments. It’s non-toxic, environmentally friendly, low-tech but high-skill, and exceptionally beautiful — great attributes in my mind. And it sounds better, at least to my ears (more details in "More about the Nylon-String Harp Guitar").