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Early maple bridge development

Bridge-by-bridge description of Bridges #1 through #15

Hello, CoMandos and other mandolin freaks-- Thanks for your interest. Here are the early experiments developing the one-piece maple bridge idea. It's simple, but it works!

All the early bridges, successful or not, are listed below. The most successful experiments were Bridges #8, #11, #12, #14, and #15, all of which feature the "winged" design. It seems to be extremely important for the ends of the bridge top to be left free to resonate in their own way, and the idea was progressively developed down to Bridge #15. After more refinements, I settled on Bridge #27 (pictured at the top of the main bridge page) as a standard model to use for the time being.

Most of the following bridges are curly maple, slab cut, 4" to 4 1/8"long, and about 1/4" thick at the base and 1/8" to 3/32" at the top unless otherwise specified.

On each bridge, I compensated the E and D strings all the way forward and the A strings all the way back, and put the G strings in the middle.

The results, bridge by bridge:

Here's a report on the first bridge. This was installed on Randy Wood #3, the mandolin which Bill Monroe owned for many years. I think that if Bill had known how this mandolin turned out, he would not have left it behind!



Bridge #1

picture of mandolin bridge
Bridge #1, completed June 14th, 2002. Somewhat crude, but very effective!

I posted this report on line:

CoMandos, I have a question for the experts, builders, repairmen, and other Illuminati, which is:

I understand that in designing their F-5 mandolins, the Gibson company applied various principles of violin construction to their mandolins, including the carved, arched top and back; the f-holes in the top; the elevated fingerboard and tailpiece. These innovations worked very well in producing tone, volume, and projection, and for many of us they define the modern mandolin.

In that case, why did Gibson stop there? Why aren't all mandolin bridges made of MAPLE, with cutouts on the principle of violin bridges? Those bridges allow no direct vibration paths from the strings to the bridge feet, but rather act almost as a spring or lever to throw the vibrations into the top. I've heard that a solid violin bridge results in a dead sound. In any case, no one would make a violin bridge out of ebony or rosewood!

And so-- Why did the Gibson company make one-piece bridges which were simple slabs of ebony? And why do we still use Gibson's pattern of ebony adjustable bridges, which channel all of a fine mandolin's sound through two metal screws? Ebony is a dead wood, the metal parts have a muting effect, and metal screws are poor conductors of the exquisite overtones in a fine acoustic instrument.


I ask this because yesterday, I made a one-piece maple bridge and installed it on a favorite mandolin of mine. The results are spectacular. The mandolin now has richness, brilliance, and volume that is hard to believe. I estimate that the mandolin gained over a third in overall responsiveness. It's as if all the other bridges I've ever used stopped up the sound in some way, but this bridge lets it all out.

The bridge is 4" long, hard, well-aged maple, about 7/32" thick at the base and 3/16" thick at the top. Finished weight is about 4.5g. Its outline is a lot like the old Gibson one-piece bridges, but with two horizontal oval cutouts. The feet are 1" long, with an low, ovaled cutout between them.

I am not an expert builder. All I know is what this bridge did for this mandolin. I urge others to experiment with similar bridges to see if we are on to something! And if you have thoughts on this and would like to share them, please let us all know.


...and here's the report on the second bridge. This was installed on an excellent 1981 Randy Wood mandolin:

Bridge #2

picture of mandolin bridge
Bridge #2, completed June 17th, 2002. The bridge top was not compensated yet when I made the scan.

CoMandos, the second one-piece maple bridge is completed and installed on a mandolin here, and the results are outstanding.

This mandolin is a high-grade F-5 copy which I refinished in varnish about 10 or 11 years ago. Since then, set up with an ordinary adjustable bridge, it's had excellent volume and a satisfying sound with lots of body.

With the new maple bridge, however, the sound took a jump. Now this mandolin has terrific volume, and it still has a pleasing tone with excellent balance. The treble strings are very clear and bell-like. The bass is dry and 'woody'. Now this mandolin's back vibrates more than any other I know, and the impact of the chunk chords (both up high and down low) is terrific.

Obviously, a maple one-piece bridge, like any other bridge, will have a different effect on each mandolin it's installed on. I encourage others to try out the maple one-piece bridge idea, and post the results so that everyone can benefit.


...and here's the report on the third bridge. This was installed on Randy Wood #3:

Bridge #3

picture of mandolin bridge
Bridge #3, completed June 19th, 2002. Smaller, lighter, results not as good!

Bridge #3 is finished. It is better carved and more artistic, thinner (3/16 at the bottom, 1/8" at the top), lighter weight when finished (4.05g vs. 4.5g for bridge #1), but NOT AS SUCCESSFUL. Volume, bass response, and that earthy, woody sound are not as great as with the first two bridges, which were thicker and heavier overall. Lightness does not seem to be the answer. I suspect that there is a minimum mass and rigidity that a mandolin bridge needs, in order to transmit the heavy vibrations to the top.

Next will be bridge #4, a little heavier than the first two. I hope to bracket the optimum bridge weight this way. Will report more results later.


...and here's the report on the fourth bridge. This also was installed on Randy Wood #3:

Bridge #4

picture of mandolin bridgepicture of mandolin bridge
Bridge #4, completed June 20th, before and after the internal oval was cut.
This bridge is a little larger than the others, and VERY successful (after a cutout was added)!

Here's Bridge #4! It's a little thicker and heavier than the others, at about 4.9g weight when finished and the internal oval was cut.

Without the cutout, the bridge was rather disappointing. The mandolin's tone was rather unresponsive, and I knew the bridge could do better. Then I made the oval cut out! And... it worked. This bridge, on Randy Wood #3, gives a loud and brilliant tone, with a solid bass, smooth highs, and amazing sustain. Right now it's cut for a high action (7/64" E, 8/64" G at the 12th fret) and I am cutting it down gradually. The volume seems to be *increasing* as the action gets lower. This was probably because I left the action too high to begin with, so that I could cut it down progressively to see the result.


Bridge #5: Larger feet, and an excellent bridge

(Sorry, no scan available. I was in too much of a hurry to hear what it sounded like to scan it before installing it, and now I like it too much to take it off!)

June 27th: Randy Wood #3 just caught fire, after I installed the fifth maple bridge. The tone, volume, and sustain have improved again. This seems even better than with Bridge #4.

This bridge gives the best volume of all the bridges, although the tone is a little sharper than with Bridge #4.

Specs: 4" long, and the outline is almost identical to Bridge #4. Thickness about 7/32" at the feet and 5/32" at the top. Weight 5 grams. Cutout 1 1/4" long. I cut the bridge outline so that the feet are a little larger, as seen from front and rear, than on the previous bridges. Both feet are 1 1/8" long, about the same as on #4. The bass bridge foot is in a knot of maple curl, which extends over half of the lower part of the bridge.

Notes: I made this bridge very thick (3/8" at the feet, 8 grams) to begin with, and began cutting it down to discover the optimum thickness and weight. At 5/16" thickness, 7.2 grams, it gave a very stiff sound. 1/4", 6.4g, was not much better, still a little disappointing. I decided to thin it down some more, and as I was doing that the belt tore up on my belt sander-- so I stopped right there and tried the bridge. Bingo...


Bridge #6

picture of mandolin bridge

Bridge #6, completed July 25th: I would call this a "90% successful" bridge. Made with two experimental circular cutouts on each side in addition to the central oval, It gave a good balanced sound with plenty of volume, but it did not give that "special" feeling of the best bridges.


Bridge #6 after modification on July 30th

picture of mandolin bridge

Bridge #6 was not special at first, but then I made two small saw-cuts into the first circular cutouts on each side-- and Mercy! The bridge suddenly gave MUCH more volume and richer tone than before. (See also Bridge #7, following:)


Bridge #7: A very successful bridge

(No scan available yet)

Bridge #7, completed July 25th: This bridge is very similar to Bridges #4 and #5, but was cut 90 degrees apart from them from the same block of maple, in fact almost quarter-sawn . This bridge is very successful, and added a pleasing increased bass response while leaving the clear, ringing treble unchanged.


Bridge #7 after similar modification

picture of mandolin bridge

After playing the mandolin with Bridges #8 and #11, Bridge #7 did not sound as good any more. So after seeing how a small change helped Bridge #6, I also set #7's top ends free to vibrate their own way. I did this by drilling two 3/16" holes near the sides of the bridge, and then making short saw cuts to open up the holes. The results were similar to those with #6: The mandolin really, really sounds off with either of these bridges on it now. The amazing increase in response, from this small change, is rather difficult to describe!


Bridge #8: The first "power bridge"!

This was patterned more after a violin bridge, and it is the best so far!
picture of mandolin bridge

Bridge #8, completed July 26th: This bridge is the first that I have made with design inspired by a violin bridge. I had been reading the theory of violin bridge function according to Sir William Huggins, an eminent British scientist of a century ago, and what he said made a lot of sense.

If I interpret his view correctly, Sir William hypothesized that in order to convert the transverse string vibrations into vertical vibrations to drive the violin top, the top half of a violin bridge needs to pivot or "swing" back and forth around a vertical axis, and then pass the vibrations to the bottom half of the bridge, which rectifies them into vertical impulses which are passed into the instrument top.

This theory explains the function of the violin bridge cutouts as facilitating this process by mechanically decoupling the top half of the bridge from the lower half. I decided to build a mandolin bridge which would work in much the same way: providing a path of transmission between the top half and the bottom half, without attaching and restricting the ends of the bridge top, so that the top could vibrate in its own way and then pass the vibrations downward. And, did it ever work!

The feet are left at about 1/4" thickness, with the bridge thickness tapering straight to 1/8" at the top. The resulting bridge weight is a little over 5 grams.

The results: The mandolin now has not only tone, volume, and projection, but POWER. The "chunk" chords in low C and B are very satisfying, really vibrating the whole mandolin. The up-the-neck chords are just as strong as before, and the intonation is still excellent. The sustain is still exceptional, but it is smoother or more "silvery" now. Needless to say, I will continue this line of experimentation. I'll build more bridges like this!


Bridge #9: made of South Carolina maple

(No scan available yet)

Bridge #9, completed July 26th: This bridge's outline was patterned after Bridge #4. It is very similar to #4 and #5 in thickness, but since the wood is somewhat lighter, the weight came out to less than 4 grams.

I would describe this bridge, like Bridge #7, as a "90%" bridge. Very superior to conventional bridges, it still did not quite come up to the very best of these one-piece bridges. I plan to make more of these Southern maple bridges, with increased thickness and patterned after Bridge #8.


Bridge #10: shorter feet, deeper cutouts, not as successful.

picture of mandolin bridge

Bridge #10, completed July 27th: I changed two things at once with this bridge: the side cutouts are about 1/8" deeper, leaving the central column 1 1/2" wide, and the bridge feet are shorter, only 3 1/2" tip-to-tip.

I should have changed only one characteristic at a time, because the bridge was disappointing and I could not tell what caused it. This bridge did give excellent volume with lots of bass and a very clear treble, and like #9, it was superior to regular bridges. However, it lacked the silvery tone and great sustain of Bridge #8.


Bridge #11: A terrific bridge!

This scan was made when the bridge had very long feet, 4 1/2" tip-to-tip, but I shortened and slimmed them down later and the bridge improved greatly.

picture of mandolin bridge

Bridge #11, completed July 29th: This bridge is similar to #8, but with slightly longer "wings" over the side cutouts. I also made this bridge a little heavier than #8 and gave it extra-long feet, so that I could reduce the foot length, the cutout overhang, and the thickness progressively to study the results.

At first, this bridge was not a great success, giving a sound like #10. After I shortened the feet to 4" total length, however, the bridge gave a much better sound. I still thought that the sound could still be improved, and I noticed that the bridge feet were a little larger in outline than on #8. So, I reduced the size of the foot outlines so that each bridge foot is now about 1/4" high and 9/32" thick.

Then, the bridge really lit up! The mandolin now has both smoothness and excellent well-balanced volume. In its final form this bridge is like #8, except that the "wings" on the bridge top are still a little longer, and the bridge is a little heavier, about 6.2 grams.

When I play the mandolin now, the sound fills the room. Stay tuned for more.


Bridge #12, made July 30th, 2002: The Complete Mandolin Bridge

This design was intended to take advantage of violin bridge design principles, and adapt them to the mandolin. Bridge #12 was also the first of many winged bridges that I made.

picture of mandolin bridge

Bridge #12: In an attempt to apply violin bridge principles to the mandolin, I made this bridge with somewhat heavier overhanging ends to the bridge top. I used simple circular holes for the side cutouts (primitive couterparts to the "kidneys" in a violin bridge) and provided only a short central cutout, analogous to the "heart" in a violin bridge. The bridge feet were originally almost 5/16" thick, with a bridge weight of about 6.25 grams.

First impressions were that this bridge did not sound as good as #8 and #11, so I began modifying the bridge to see what could be done to the sound. The bridge feet were a little long at 4 1/8" total tip-to-tip length, so I cut them down until the bridge was only 4" long. This helped somewhat. Then, I thinned the bridge so that it measured 1/4" thick at the feet and about 1/8" thick at the top, like #8 and #11. This seemed to help considerably, and reduced the weight to under 6 grams, but the bridge was still falling short.

Finally, realizing that I had changed the bridge feet quite a bit without rechecking the fit, I re-fit the feet to the mandolin top. This was just what the bridge needed! Suddenly the mandolin had a tremendous volume, with great sustain. Up-the-neck chop chords, as before, were excellent. But the best part was that the mandolin's bass response-- which no bridge had yet brought out-- was suddenly brought to the fore, with a great "meaty" feeling to the bass and good vibrations of the mandolin's back against the player.

This is the best bridge yet, and it seems to indicate that leaving the bridge top free to vibrate gives a great responsiveness to the instrument. The modifications I made today to Bridges #6 and #7 (see above) indicate the same thing. Now bridges #6 through #14 all leave the bridge top free to swing and resonate in response to the strings, to vertical ones, and ALL of these bridges have excellent volume and sustain. This may be a major principle of future bridge design.


Bridge #13, made August 1st, 2002:

This bridge was made with the conventional outline of #1 through #7, but with the bridge top ends cut free to vibrate on their own.

picture of mandolin bridge

The bridge was also left extra thick as an experiment. Thickness at feet, 9/32". Thickness at top, 3/32". Weight, 6 grams.

This bridge gives excellent volume and sustain. Although the richness of sound is not quite up to #8, its bass response is a little better and it is a really excellent bridge. I suspect that the extra thickess may contribute to the bass response, since a certain minimum bridge mass may be necessary to communicate the heaviest vibrations to the mandolin top. I went immediately to finishing the next bridge, #14.


Bridge #14, made August 1st, 2002:

This is a visceral bridge!

picture of mandolin bridge

Bridge #14: This bridge was left with the same thickness as #13, but with a very different outline from any previous bridges. Desiring to take fullest advantage of the "winged" concept, I put as much mass as I could into the ends of the bridge top, extending them all the way downwards to the tips of the feet. This gave the bridge more mass overall than any of the previous (successful) bridges. Finished weight is 6.7 grams.

I call this the "visceral bridge" because of its great bass impact. The sound maintained the volume, sustain, and tonal richness of the previous winged bridges while adding considerably more "punch" in the bass, even more than in Bridge #12.

This mandolin is now extremely satisfying to play. I believe that the value of the "winged" bridge design concept is now fully established, and my future experimentation will be along these lines.


Bridge #15, last modified August 6th, 2002:

Originally, not successful; after modification, a great bridge!

picture of mandolin bridge

Bridge #15: This bridge was made from some European maple which seemed to have been cut for violin bridge wood: the "speckled" grain was conspicuous in the wood. I left the bridge a bit thick and heavy to begin with, with straight diagonal wings, so that I could modify it as I went along to observe the results.

At first, this bridge was not exceptional, falling a little short of Bridge #14 in the overall responsiveness which it gave. Then I thinned the bridge slightly and rounded the wings inwards a little. The bridge really woke up! Suddenly there was a bass richness which this particular mandolin had never shown before. I also noticed that I had accidentally left the treble bridge wing a little larger than the bass wing.

Hoping to follow up on this success, I thinned the bridge a little more, and reduced the wings just a bit more. To my disappointment, the bridge was not improved, and seemed to have lost a little of that exceptional bass response.

After a couple of days and some experiments with modifying previous bridges, I returned to Bridge #15 and modified it the same way, extending the round side cutouts inward toward the middle of the bridge:

picture of mandolin bridge

...and I am now very happy with the sound. This operation brought more bassy richness into the sound, and the mandolin still has plenty of treble cutting power left (since it had so much to begin with). I've kept this bridge on the mandolin for over a week, an unusual thing for a bridge these days!

To drop me a line, just click here.

Red Henry.




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