|Pursing the ALMOST Brace-less Soundboard
|By: John Alden Robinson of Maliposa Music
In the days of yore to build a brace less top was implausible because the strength of materials did not allow for it. A top
built of traditional materials in order to withstand the stress imposed upon it would have had to been so thick it would not
have been very resonant. Builders resorted to many different brace patterns to strengthen very thin and weak tops to
maximize the sound.
The discussion as to the location and the proper shaping of the bracing, still hundreds of year’s later, rages on. One of
most knowledgeable of this field is Scott van Linge a traditional builder who I have worked with in my soundboard
development. Mostly he as evaluated my guitars. In his defense he told me “I haven’t clue as to what you trying to do.”
With the advent of advanced composites materials, brace-less tops have now become possible and many notable luthiers
are currently building guitars this way -Charles Fox for example. However, some of these luthiers have fallen into
In making their tops strong enough to support all the loads without braces they have developed a very uniformly ridged
top. The results are a loud commanding but harsh sound. The sweetness, the mellowness, the color and body of sound,
and as suggested the soul of a guitar, that comes from a well made and braced guitar are the results of parts of the top
being able to flex more than others. Thus, one of questions we have to wrestle with is do we really want a brace-less top?
At a guitar convention in the summer of 2006 I looked at Charles Fox’s work and suggested:
|“Why don’t you try putting the braces between the layers of your top?”
-He calls his tops sandwich tops I prefer the term: Biplaner -as in two planes of wood and from biplane airplanes that I
used to work on.
I started working on airplanes and musical instruments at about time. When I was fourteen. I started
on wood biplanes and advanced with industry into aluminum and finally advanced composites
especially the composites of sailplanes. I have had thirty years in aviation industry and forty years of
building musical instruments.
He looked at some of my work: fan-planked Balsa-wood and carbon fiber soundboards, carbon fiber and birch braces
for steel-string guitars less than a ¼” thick and issued me counter challenge:
|“Why don’t you build a brace-less top.”
I took up his challenge and have had good success with my almost brace-less tops -the 2V2X top. I am continuing to
perfect the 2V2X. and have created 2 more types of tops -The MMX and FB5M. So I would like to share some my
observations and work leading up to my almost brace-less soundboards I am now building. I have found in my work that
building a steel string guitar soundboard is divergent from building a classical guitar soundboard so I will start with steel
string sound board that I have had the most experience with.
Part one: The Almost Brace-less soundboards for Steel-String
I built several guitars in the Seventies during that phase of my building I was introduced to epoxies and carbon fiber by
one of my students –a boat builder. I adopted them very quickly into my work -primarily in the neck. I found that six
layers of uni-directional carbon fiber would flex more than two layers of carbon fiber separated by compression medium
(mahogany). It was reminiscent of biplane construction, and I beam design. Compression/tension members separated do
not have to be as strong as solid member. I stop building in mid-Eighties.
Lightness in a top makes for a louder guitar so when I started building again in 2001 I tried to sandwich two layers of
redwood separated by a mesh of fiberglass and was unsuccessful -my first attempt at a Biplaner tops. That research
progressed on and I found that I could use 2 oz fiberglass with epoxy resin on both sides of a redwood top and it would
greatly strengthen the wood and prevent cracking. I could now build tops as thin as 0.045 and probably thinner but I
never tried. The fiberglass did not seem to affect the sound of the wood. 2 oz or lighter Fiberglass when done well will
disappear and leave a finish looking like a well-done clear finish.
Lesson: If 2 oz fiberglass is applied to only one side of the wood, it kept the wood from cracking but did not
strengthen the wood. It allowed the wood to flex as if the fiberglass was not there.
I used fiberglass inside or on the underside of spruce tops for several of my instruments.
My work moved on to using balsa wood with inner layer of carbon fiber and outer layer of 2 oz. Fiberglass. At 0.050’
these tops were incredibly light and strong. Balsa wood has density of 9-10 pounds per cubic foot. A special Balsa wood
is also available with density as low a 4.7-6 lb/cuft. Spruce is at 30 lb/cuft and Cedar is at 20 lb/cuft. Balsa wood comes
from the South American rain forest and is a pioneer species; it is the first tree to grow after clear-cutting. It is a very
plentiful and often cleared to make room for more valuable species of trees. It is weed or a garbage tree, so use it, and
do not feel guilty about it.
|There are a couple of problems with balsa wood:
One, the widest you can get of Balsa wood is about 4” with 3” being the most common size. That means numerous
seems in a top.
Two, -James Hamm of Vancouver currently in production of cellos of balsa wood- suggest to me at the same
convention, “Balsa wood deadens the higher frequencies and balsa wood tops are probably better suited for steel-string
guitars then classical guitars.” I suggested to him that the wrap of fiberglass and carbon fiber changes the way the wood
responds and yes the higher frequencies will come through. He carefully documented what I had told him and I suppose
he is experiment with laminating fiberglass and carbon fiber on his cello tops. I have since stop building classical guitars
with balsa wood tops. During this period I had not perfected a brace pattern as if any one ever does with may be with
the exception of Scott van Linge.
I next developed braces that worked (but far from perfected) and a new top. In
Phoenix Arizona there is no store where you can go pick-up pieces of spruce or
cedar and hold them to make your selection. That was why I decided to develop a
top that used tapered pieces of balsa wood with uni-directional carbon in between.
The concept came form the ramblings of Ervin Somogyi “The dark wood does all
the work in the top and light wood just goes along for the ride”. So If I made the
dark wood uni-directional carbon fiber and the light wood the lightest thing I could
find -balsa wood- which produced a very light weight, artificial but extremely
predictable tops. One of these tops with traditional bracing will produce a beautiful
more full sound with a boomy bass and mellow treble and much louder than spruce.
However, they are very protracted and challenging to make. Originally I used layer
of 2 oz. Fiberglass on the inside and out side for additional strength. These tops ran
about 0.055”. I found if I dropped inner layer of fiberglass leaving just the outer
layer of fiberglass for protection and increase the thickness of the wood it made the
sound even fuller. I was using .128” at this point.
Lesson: Carbon fiber and fiberglass is stronger in layers separated by a good
Lesson: Thinner is not always the answer.
Lesson: Steel-string instruments are best with the lightest woods tops even
thought it seem to be discouraged.
This is where Charles Fox issued his Challenge.
|“Why don’t you build a brace-less top.”
Attempt 1: So I did using my fan planks balsa wood carbon fiber top.
The top was used as a display and already .128” I added several layers of
balsa wood and fiberglass in circles of different sizes to approximate a
cone under the bridge. I was unsuccessful in making it a brace-less top in
that it required two braces .250” thick to make it strong enough.
Attempt 2: I decided to build a Biplaner top for a twelve-string guitar and
place the braces between the layers. The outer skin was Molted Aspen
0.032” and I made a brace pattern in the form of a spider with layers of
carbon fiber and Birch in my leaf spring concept. The inner skin was of 2
oz fiberglass. The top was not strong enough in spite of adding two more
layers of 2 oz fiberglass. I had to add layers to the braces on the underside
of the top.
Lesson: The making of Biplaner tops using this method is almost as
time consuming and laborious as my fan-planked carbon fiber tops.
Lesson: Biplaner tops are not lighter then the way I was already
building tops nor was the sound as good.
Lesson: Biplaner tops are not as cost effective as methods I was
Attempt 3: I started with a top of my fan-planked balsa
that I sanded down to .200” Then I add at 90 degrees
planks of balsa and carbon fiber in an oval. These planks
had to be fitted to the top. My tops are arched or cylinder
formed ¾” in the width of 16” like Tores. I still feel that
building on a sphere inhibit sound especially if you get in
range of a 12’ sphere. [I even feel building on cylindrical
shape inhibits vibrations and now build a flat top but it is
sculptured.] The oval or cross laminate planks had to be
sanded down by hand to get the right amount of flex in the
top and blend in. Under the bridge the top was .385”. This
tops was successful and one my best sound instruments
and most time consuming and difficult to make. It also had
some problems that Scott van Linge found -dead spots
where the inner oval was not blended well enough.
Attempt 4: I decided to simplify my top making procedure:
An outer skin of Prima Vera .050”, a carbon fiber brace
pattern three layers in tapering lengths on the Prima Vera
Lesson: This was not an acceptable way to build a top for a steel-string guitar because the top was too stiff to
allow the bass to come out, but it may have application in classical guitars
Attempt 5: I like to give my tops and their brace patterns a descriptive name this top is
my 2V2X top. An outer skin of fan/planked balsa wood carbon fiber of .050” with 2 oz
fiberglass on the surface -for looks primarily, -I decided that outer skin could be of
almost anything that is appealing-, tapering carbon fiber brace pattern three laminations
thick, 1/32” balsa wood at 60 degrees to centerline, a second lamination of 1/32” balsa
woods at 60 degrees to the center line in the opposite direction with 2 oz fiberglass, on
under side, a repeat of the carbon fiber brace pattern only one layer thick because the top
was strong enough. –Top on the same guitar as above- Sounded very well not as full as I
like but the guitar was an El Poketo -a very small guitar. Scott van Linge’s
pronouncement was: “It’s the best balanced of the three guitars.” That I brought up to
him on his mountain shop.
|Question: Placing layers of carbon fiber between layers of
the top and on the underside of the top to stiffens the top in
selected areas does the same thing as braces on the under
side of the top; but are they braces?
This is why I choose to place the qualifier ‘ALMOST’ in my title.
Lesson: This method of top construction is much easier than most I have tried and with very agreeable results.
Lesson: Carbon fiber strips can be added or deleted to get the desired strength of a top on the underside only.
You can even if necessary at this point add traditional type bracing.
Lesson: Carbon fiber can be carefully sanded to control the strength.
Attempt 6: The second 2V2X top on an El Cornkeestador. An outer skin of
Western Red Cedar from LMI .050” (WITH NO 2 oz fiber glass, just wood) a
carbon fiber brace pattern of three tapering layers, a 1/32” Balsa wood at 60
degrees to centerline, a second lamination of 1/32” balsa wood at 60 degrees to
centerline in the opposite direction, a third layer of 1/32 balsa wood in line with
centerline, at this point the top did not feel stiff enough.
Lesson: I have since found is that the resin continues curing for up to seven
days and If you test a top the next day it is far more flexible than it is a
So I added a fourth layer of 1/32” balsa also in line with centerline, and a repeat
of the carbon fiber brace one lamination thick.
Upon testing the top is too rigid for a six-string guitar so I decided to complete the
guitar as a twelve-string. We’ll see what it sounds like. It is about 0.190” at the
edges. The fourth layer of balsa wood was unnecessary. On this top I’m trying a
dome but not like most builders my dome rises out of the curved plane of the top
-in side profile it has an S curve like carved arch top guitars. It is almost
imperceivable unless look and feel very carefully.
The guitar has been completed and it very heavy being the back, sides and neck
are of Bubinga It has a very full sound ample bass and ringing treble. It was the
best of my 12-strings to date. Neck junction at 18th fret.
Attempt 7: Third 2V2X top For a
Rewnasance. Outer skin of red wood .
070”, channels .030” deep routed in the red
wood for the upper layers of carbon fiber
pattern. The channels with the carbon fiber
were leveled with ultra light epoxy faring
compound, a 1/32” Balsa wood at 60
degrees to centerline, a second lamination
of 1/32” balsa wood at 60 degrees to
centerline in the opposite direction, a third
layer of 1/32 balsa wood in line with
centerline, and a repeat of the carbon fiber
I was doing well with my cross laminated tops with outer skin of traditional tone wood with two internal layers of balsa
wood and the internal/external carbon fiber strips, until I tried a different resin. The resin base was more viscous and did
not’t penetrate the balsa wood like the resin I had been using did. I had my first guitar failure in Arizona as result of
changing resin. The neck block separated from the sides of the guitar and the top. The top had sheared not in glue joints
but the balsa wood it self!
|I resolved to get all balsa wood at that point out of my
construction. I moved up the wood scale to the next lightest
Woods -basswood and poplar and alder.
I was at this point having some success with Biplaner top in my classical guitars. The next tops were biplaner with
external skin of a traditional tone wood-the one that sets the behavior of the top- internal Nomex and carbon fiber
bracing followed with an inner skin of basswood and carbon fiber bracing. This has worked out well and I am still
refining how thin to make the carbon fiber strips almost all tops are still coming out too strong.
The I came up with a method of sculpturing the
tops so they are the thickest where the maximum
loads are placed on the top -the bridge area to the
neck block- and the thinnest were the loads are
minimal –at the edges and below the bridge)
Part two: The ALMOST brace-less top for Classical guitars.
There were three classical guitars build using my fan/planked tops. The first
used a pennant lattice brace pattern. It was pretty sounding but lacked a
‘chiseled treble’ next was a lute shape with the first pennant triple X bracing
better. Third was special top using contest balsa it had a density of about 5
lb/cuft. With the pennant triple X bracing. It was good but still not what I was
searching for. So I started by designing, a new model guitar. People comment:
‘it actually looks like a guitar’ it is symmetrical from side to side. It had brace
under a center sound hole that confines the sound to the lower lobe like a
Lesson: Light densities tops are good for steel-string and not for classical guitars.
Builder of the finest classical guitars I have heard insists on German Spruce. It runs from what I can tell heavier than
Sitka Spruce and a deeper tap tone. Although I rejected using Biplaner tops initially on my steel-string guitars it seemed
very promising for my classical instruments. Fritz Muller of Northern B. C. builds using this method but still uses braces.
From Fritz’s writing: ‘The outer skin determines much of the characteristics of the top.’ So the choice of the outer skin
is the most important.
Attempt 1: Red wood outer skin of .045” with Classical 2V2X carbon fiber bracing two tapered layers in only the lower
lobe, Nomex glued over the carbon fiber and sanded to make constant thickness over the top, a inner layer of 1/32”
balsa wood, a repeat of the carbon fiber brace pattern, External brace (not in the top but inside the guitar) below the
sound hole. It was still lacking so another guitar was built with refinements to body shape. I decided to try something
different. Heavier woods tend to dampen the bass, which is strong in a classical guitar, and promote treble, which is
Attempt 2: A Prima Vera outer skin (density 45 lb/cuft)
0.040” thick, 2V2X two tapered layers of carbon fiber in only
lower lobe, Nomex sanded, an inner skin of a special
directional fiberglass of 70-30% strength ratio approximate
that of spruce’s strength ratio. Below sound hole an external
As note, it had a beautiful sound but lack command -volume.
Year later the fiberglass/resin under skin had creped and the
top was very distorted to point where I am now replacing it
with a sculptured biplaner fan-braced top.
Lesson: The Biplaner top can cut the density of overall top so heaver wood selection can be explored for use in
soundboards of classical guitars without the normal penalties.
From my success with sculptured biplaner tops with steel
string guitars I it brought over to my classical guitars. To
right is current sculptured Biplaner FB5M (Fan Bracing 5
I continue to build classical guitars primarily for the challenge
and the education; tt has not been for customer patronage or
for the gratification they bring me.
Steel-string guitar player seem much happier with their
|All I will say is after all these years the more you learn and
experiment the more you realize that there is so much more
that you still do not know. I am willing to consult in hope we
will find that superior method of construction and save other
the aggravations of repeating my work
John Alden Robinson
17415 N. 75th Ave
Glendale, AZ 85308
|El Poketo with fan planked
balsa wood & carbon fiber top
The first Almost Brace-less top for
2 or had been 3 years and the guitar
is doing well and sounds well.
Biplaner spider braced
It was sold. Note 22 fret
–as close as I can come to parabolic with unidirectional carbon fiber-, A layer of carbon fiber plain weave 5.7 oz, a
layer of 1/32” balsa wood at 45 degrees to center line, a second layer of balsa wood at 45 degrees the opposite
direction, and a inner layer of carbon fiber plain weave 5.7 oz. At this point I tested the top for deflection under string
loading. It was so strong that it only had a .015” deflection above the bridge and .020” below the bridge. I was intending
to match the carbon fiber brace pattern on the underside but there was no need. -Top installed on a guitar- It was very
loud, harsh and the bass was poor. It was reminiscent of Charles Fox’s classical guitar I heard at the convention.
|El Poketo With the first
Pattern. The top after testing was not strong enough and required under side bracing. Small Alder strips ¼ wide by 1/8”
thick with one layer of Uni-directional carbon fiber over them. The Redwood was less rigid than the Western Red Cedar
Left in a biplaner top with 2V2X bracing still too
heavy! The inner skin is hemlock. Some builders
say hemlock is superior to spruce in sound
production, especially in classical guitars. I have
found a source of hemlock veneer that is ready for
lamination making building a biplaner top much
easier. If someone would offer a spruce veneers I
would use it, but hemlock is working exceptionally
I have returned to a more traditional design of guitar -symmetrical with a sound hole under the end of the fingerboard
(the worst possible place to put in a guitar soundboard) in hopes of more appeal. With this reversion I have developed a
new top brace pattern that is similar to Martin X. I have given it the name MMX (Modernized Martian X)
|This is a MMX top for a Nazarene Star (Dreadnought). I
have finally after 40th years built a copy of a Martin. The
outer skin is Stika Spruce it has three graded layers of
carbon fiber bracing on it and the Nomex honeycomb it
has been sanded and sculptured the carbon fiber bracing
can be seen through the nomex. The lighter areas of the
Nomex are where it is thinnest so you get some feeling
for the sculpturing.
This is a MMX for top for Southern Star (Gibson's
Southern Jumbo or J-45) It is almost finished and
ready for installation. There is a triangle of carbon
fiber that goes from center X to under the bridge
missing that the string and bridge pins go through.
Most people are amazed at how low the profile of
the carbon fiber braces are.
This top I think is on the Southern Star that built for
Larry Jackson of Southern Star Bluegrass.
|Classical guitar with 5-6 lbs per
cubic foot fan planked balsa
wood & carbon fiber top
Pennant Tipple X
|Outer skin with carbon fiber before the Nomex
|Top just before installation