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For those of you who my be interested in harp guitar construction, here is an article I wrote in 2005. It's pretty technical but I describe how I worked with a client in collaborative design building my first harp guitar.
The following article appeared in "Guitarmaker: The Journal of Fretted Instrument Construction and Repair" Winter 2005 Issue 50:
When I first heard Stephen
Bennett play a harp guitar on stage I knew right then I had to
build a harp guitar of my own but, like most instruments I dream
of building, reality said I needed to wait for a customer to come
along and pay me for my efforts. And so that opportunity came
as a guitarist, who wished to distinguish himself from the ever-growing
pack of instrumental finger stylists asked if I could build him
a harp guitar and, never having built one I said what any enterprising
luthier would say, "sure I can do that, no problem."
Well as it turns
out there were a host of technical problems to overcome in building
such a complex instrument. But this customer gave me enough direction
to go on while still leaving plenty of room for interpretation:
He wanted something based on the Gibson model U and he wanted
it to look magical and eye catching, sound light and airy and
be built for not too much money.
The Gibson Model U was made as a regular production guitar in
the first few decades of the 1900's in several configurations
of stringings and embellishment. As opposed to the Dyer style
harp guitars which have an elongated soundbox to support the harp
strings, the Gibsons had a separate guitar body with a pillar
neck to support a second peghead bridged to the peghead of the
guitar neck. Compared to the Dyer style harp guitar this simplifies
construction as separate necks can be attached to a body, oversize
pieces of top and back wood are not needed and for the player
results in a more compact instrument that is easier to hold and
carry.
The design:
The customer and I worked in close collaboration on the design.
I made full scale drawings on poster board, cut them out, studied
them for a few days and we eventually got to a configuration we
agreed on. We settled on having 6 harp strings with cedar for
the top for a light airy sound and black curly walnut for the
back and sides which I could get in planks and resaw for the sizes
I needed. A body width of 16.5", smaller than the original
Gibsons, makes the body easier to hold.
The plates:
Since the carved top Gibson harp guitars have been said to often
be lacking acoustically to the point of comparison to a dresser
drawer we decided to build a version with a flat top and back
to provide a more modern guitar sound. The top was left rather
thick at .140" at the center tapering towards the edges and
was braced with a double X brace to create a 25 foot radius arch.
The back was braced with ladder bracing to a 15 foot radius. The
double X brace needs to be splayed to allow enough room for 12
or more strings across the bridge plate.
A K&K Sound pickup was custom made for this instrument with
6 individual sensors glued to the underside of the bridge plate,
3 for the harp strings and 3 for the guitar strings wired into
a stereo jack to allow the two sets of sensors to be blended in
an external preamp.
The
body:
The body construction was fairly straight forward with a couple
of exceptions. The big "Mickey Mouse ear" requires side
wood considerably longer than a standard guitar and needs to be
bent into a tight curl by hand. The harp pillar, extending through
the body for more rigidity, is let through a square hole in a
block at the top of the "ear" and is held in a pocket
at the opposite end of the body.
While the sound hole is on the centerline of the top, the guitar
neck is about 1.25" off from the centerline of the top allowing
the 12 strings to be centered on the top. l build with lot of
jigs and quickly discovered that being somewhat large and oddly
shaped the harp guitar parts wouldn't fit my standard jigs so
much of the work needed to be done by hand.
The back was left off until the basic geometry of the necks was
established in order to provide better access inside the body.
The neck and pillar:
The guitar neck is pretty standard fare except that the peghead
is kept longer to allow the harp neck something to attach to.
The pillar which runs through the body is bolted to the body from
the outside. I like to bolt things together when possible for
easier disassembly should a neck reset or top replacement be necessary
in the future.
The pillar supports the harp "peghead" which is bridged
between the pillar and the guitar neck. This adjoining harp peghead
which carries the tuning machines for the harp strings is fairly
complex as it has to not only hold the strings but has to match
the angles of both the neck and the pillar. 4:1 planetary geared
banjo tuners were used for the harp strings.
Strings:
Gibsons usually had 10 sub basses, though had some had more, some
had fewer. On this particular harp guitar we used 6 sub bass strings
although the customer replaced to the bass strings with the octave
strings from a 12 string set to give the harp strings a brighter
sound which he prefers.
There are no standard tunings of the sub basses as each harp guitarist
finds the tunings that work best for their playing. The sub bass
strings on this guitar are 33 inches long but on subsequent harp
guitars I have used progressively longer string lengths for the
lower notes. To calculate the strings gauges and lengths needed
to get specific notes you can use the formula:
Where
D is the string diameter in inches
T is the string tension in pounds, usually in the
range of 25-35 lbs for steel strings
f is the frequency of the desired note in Hz, the low E
string on a guitar is 82.4Hz
L is the vibrating string length in inches
d is the density of the string in pounds per cubic inch,
typically .26 lbs/cu-in for a wound steel
string
Once the harp guitar is completed you can experiment with different
gauges to fine tune the sound.
The result:
The customer of this harp guitar, Echo Greywolf was thrilled with
the result. He gets plenty of attention even when practicing.
Crowds gasp when he pulls the instrument out at the beginning
of a performance. He has recorded a CD with this harp guitar which
has been nominated for awards. It has taken his music far beyond
what is possible with only 6 strings.
Many guitarists look at a harp guitar and are completely puzzled
by how one would ever play such a complicated looking thing but
it is after all just a guitar with some more strings along for
the ride which, even if you don't occasionally pluck one of the
harp strings here and there, still fill in the sound with their
own harmonic resonance.
On the other hand are guitarists who want a new instrument eager
to advance their artistry. The problem for them is that the only
harp guitars available for purchase are either delicate antiques
of a century past or custom built creations of a luthier so labor
intensive as to be far out of the price range of most musicians.
This particular harp guitar took about 260 hours to complete but
subsequent ones of similar design have taken less time.
Harp guitars are as varied as the people who play them and there
are so many configurations of strings and necks and tunings, it
can be confusing as to where to begin. A simplified version of
the Gibson U style harp guitar is a good place to begin for a
luthier contemplating a harp guitar project.
As opposed to the relatively conservative constraints of most
6 string guitars that can't stray too far from an accepted standard,
with harp guitars, both for the luthier and the player, the possibilities
are limitless.
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