Optimizing Guitar Bridges
John Alden Robinson of Maliposa Music
Introduction:
I started guitar building in the early seventies, feeling that much could be done to improve current guitar
designs. I though Dr. Kasha work had some promise so I built many failures following his design. I had given
up on his designs and decided to try to improve my banjo bridge. The footprint of the bridge on the head
should be it’s widest under the bass string and its narrowest under the treble strings of my banjo. My Banjo
was six-string (a five-string with and extra bass string so each end of the bridge foot print was to be very
narrow and widest under the fifth (fourth) string. So my bridge had an elliptical airfoil shape. (You may obtain
free pictures and text on the bridge at my web site
Maliposamusic.com). The shape dramatically improved
the sound of the banjo. With my success with the banjo bridge I decided to do my own research on guitars.
Content:
For the bridge, I placed two matching rectangular blocks, one on the top side, and second on the bottom
side of a piece of canvass screwing them together. I stretched canvass over a cardboard box so that the
blocks were suspended in the middle of the box. I pushed the blocks back and forth as if the bridge was
rocking as the theory states.
An ellipse formed in the
canvass. There were tidal
areas above and below the
Blocks as well as at the
ends of the blocks. The
area at the corners of the
blocks seemed to be under
excessive stress.
The conclusion I drew from this is that best shape for a guitar bridge is an ellipse formed by the following
method:
Measure the width of the soundboard or top
(perpendicular to the top's centerline)
through center of the saddle.
Take this measurement subtract the
thickness of the sides and side-linings if you
have not already done so to find the effective
width of the top measurement and subtract
the it from total width.
2) Find a piece of scrap wood and drive in
two nails (or screw in two drywall screws or
two small pegs would also work) with the
same distance as your effective top
measurement.
3) Place a piece of paper between the two pins/nails/screws so it is more-a less centered and tape it down.
4) Draw two lines by placing a straight edge against your pins.
5) Mark the center point between
the two pins. Used a pair of
dividers to find the center point.
6) The length of the bridge is
open to debate; but, I feel at this
point is should be half the
distance of the width of the
effective top measurement or
wider. So once again, take up
your dividers and split the
difference between centerline
and your pegs and make a mark
on the paper between the two
lines between your pins this will
make a bridge half the effective
width of the top. I’m now
7) The width of the bridge at the centerline determines what range it will be an effective driver. If you get
your bridge too narrow the bass will suffer and the treble will be pronounced. If it is too wide the bass is
prominent but it will dampens all frequencies. I feel that optimal is just little wider than what is in use now,
but that is to taste of the player.
8) Another question we have to ask before we can continue: Is the saddle the center of the bridge and the
rocking point or is it center of the bridge itself? I feel one should endeavor to get saddle as close to center of
bridges as possible for efficiency reasons; however, we live in real world where we have tie blocks (do not
use them if you can possibly avoided it) bridge pins or just anchor holes that take up part of your bridge. So,
in the real world (not using a tailpiece) measuring up toward the nut end of the bridge from your centerlines
marks between your pins make a mark 1/3 of the total width of your bridge above where the saddle will be
located and below your saddle center point, make a mark 2/3 the width of your bridge. So, you have a mark
on the centerline 1/3 of your bridge width above and another mark 2/3 the width of your bridge above and
below your centerline between your pins.
9) Take a flexible metal
strip/scale ect. and put it
against your two nails and
push up on the scale/strip
until it is on the 1/3 mark
above the saddle line
between your pins. Trace the
arch on the your paper. Now
take the strip and do the arch
below on your 2/3 mark below
the saddle and trace the
ellipse it formed.
My work shows that if your bridge ends are within the ovals there is no worrying about stress cracking and
any bridge end shapes are acceptable. It is only areas out side the ovals of the bridge that will cause stress
cracking. Scott van Linge suggests that we rounding the ends of the bridge to reduce cracking the
soundboard. I concur with Scot on making them round for a different reason. “Blending” the bridge with the
top is a major consideration of the van Linge’s theories. There should be no abrupt transitions from
soundboard to the form of the bridge. The ‘Cliffs of Dover’ at edges of a bridge design will result is dead
spots or quiet notes when the van Linge ring of activity passes under the bridge. Depending on number of
things: bridge size top density top stiffness, it can occur on notes on the B-string or high E-string. I used to
have problem with F F# on my high E-string. The more well, a bridge is blended to the top and “flows” with
the top the least impact it will have on deadening a note and transition will be smoother to higher notes in or
under the bridge. That is why earlier I suggested that the bridge be half the distance of soundboard. I’m now
using bridges that cover 5/8 of the soundboard.
By pushing out further like 5/8 or 2/3 or even ¾ of the
soundboard it will move the bridge deeding onset into lower
frequency and may be more easily dealt with making the
transition smoother. The least graduated parabolic curves in all
directions are indicated in bridge construction. So make the
ends round.
The bridge tracing pictured below is for a classical guitar and it
is amazing how close it actually is to what has been used for
years!
An almost completed
bridge on La Classikal.
A Bridge on a 12-string El Cornkeestador
Here are 6 of my ‘robo’
sanding templates profiling
6 of my bridges for 3
different instruments. The
classical guitar (La
Classikal) we are trying for
high frequencies so it is a
very narrow bridge. To your
left is ½ distance of the
soundboard bridge and
pictured in the web site. To
its right is a 5/8 bridge
noticeably thinner.
The El Cornkeestador we are trying bring out the
bass so it is much wider, although the width of top
is the same. The Renewsance the top is an inch
narrower than the El Cornkeestador but the bridge
is the same width. See the difference in the curve
and the length of the bridge.
John Alden Robinson
experimenting with the bridge being 5/8 the width of the top and have had such promising results if is my
recommendation. So you will have to dived into eights and use five of them from the center point.
John Alden Robinson
jrobinson@maliposamusic.com
Malipaos Music
17415 N 75th Ave.
Glendale, AZ 85308
Maliposamusic.com
3) Place a piece of paper between the two pins/nails/screws so it is more-a less centered and tape it
down.