Bridge design for archtop guitars

[Beate Ritzert]

Well, here to the general aspects of the design of archtop bridges. I would like to learn more on its effect on the effect on the acoustic sound of the guitar.

I am aware that at least some aspects of the bridge extremely important for the sound. First of all positioning - even a few tens of millimeters of a (correctly adapted) bridge has a very noticeable affect on the sound. Same as with violins.

But there are other possibilities:

- one piece/two piece (adjustable / non adjustable)
- two feet / no feet (selmer maccaferri style)
- thickness of the bridge (better abouzt 10 mm or better closer to 20 mm at the feet?)
- shape - should i be as straight as possible
- choice of wood (i am pretty satisfied with the katalox bridge of my electric bass)
- height of feet:

"cello like" like that one


or a maccafferi bridge or something in between?

To summarize, i would like to learn how to control the sound of the guitar by the given parameters.

Thanks

Beate

[Patrick Hanna]

Hello, Beate,
That appears to be a beautiful guitar, and I would love to see more pictures which show the instrument overall in its beauty.
As to your questions about bridge design, I am sure some experienced builders will chime in with their opinions and personal observations.

I am no expert on bridge design, so I can only tell you this much from my reading: Opinions vary among builders. Jimmy D'Aquisto favored solid bridges with a fairly massive foot design that makes full contact with the top. Linda Manzer seems to favor the same.
John D'Angelico (D'Aquisto's mentor) seemed to favor less massive bridges with a smaller footprint, but I believe they were all in full contact with the top. Other notable builders favor one approach or the other and I am sure they all produce very nice results on their instruments. Robert Benedetto, in his DVD course, insists that smaller bridges produce a better, more responsive sound. On HIS instruments, I am sure they do. The great factory makers of the 30s and 40s tended to use smaller bridge footprints, but I believe they all had full contact with the top. What I am trying to say is that they ALL seem to work very well on those individual guitars.

In no way am I discouraging you from your "cello-like" footprint, with two feet. I personally believe the field of bridge design is very open to experimentation, and I believe the perfect bridge gets married to the perfect guitar in an individual union.

Thus, I encourage you to experiment. Bridges are relatively easy to make and easy to switch out. I think you should consider whatever feedback you receive in subsequent posts here, and then build two or three or four alternate bridges for your guitar and simply try them out. You will soon know which design works best for your particular ear and concept of how your guitar should sound. I don't think you can go wrong by doing this. And I'm pretty sure they would all sound very nice. We might have our individual preferences, but we'd like them all.

Bridge wood selection undoubtedly matters, too. Again, the field is open to experimentation. I recommend that you let your own ear be the final judge. I see no reason why your cello bridge design couldn't be just perfect--as long as it achieves your goals for sound.

Now, that's an amateur's feedback. Wait for the more experienced experts to chime in, and listen, but remember that there is nothing wrong with experimentation and I encourage you to do that.

Patrick

[Michael Lewis]

Full contact base and adjustable saddle seems to work very well. It is a traditional approach. I have experimented with changing the mass of bridges thinking the lightest ones would provide the best and loudest response, but that is not necessarily true. Some heavier bridges can sound very good.

The bridge is one component in a system where all the parts work together. If you change one part it becomes different how it relates to the other parts. I know this seems like just a lot of words saying nothing but there are no rules to tell us what a system (instrument) needs because each instrument is at least somewhat unique compared to others. A lighter bridge MIGHT make your guitar sound better but also a heavier bridge MIGHT make it sound better, and you can't know until you try them.

A fellow by the name of Red Henry has a web page on one-piece mandolin bridges discussing various changes and designs which you may find interesting, but traditional bridges have worked well for many years. As Patrick suggested, to find out what works best you will need to experiment.

I generally use full contact bridges on my carved instruments for structural reasons, as it helps keep the arch across the top smooth. Sometimes a top will deform to conform to the pressure exerted by the bridge, and I have seen cracks form in tops at the edges of the bridge 'feet' that are short or interrupted with a cut out section in the middle.

[Andrew Porter]

Red Henry page: http://blog.murphymethod.com/category/mandolin-bridges/

[Beate Ritzert]

Thanks very much. That's a really interesting article. Red Henrie's winged bridges are more or less built like violin bridges. I am a bit surprised that such a construction increases the sustain (which i always have considered an unwanted property on violins).

But nevertheles, it is probably intersting to try.

[Michael Lewis]

One can not always believe what is stated by other persons, especially when they are trying to sell something. Sometimes it is true and sometimes not. When it comes to describing improvements in tone many claims have been made for various 'improvements' and some people can hear them and some people not so much. Trust your own ears.

As for making adjustments to bridges, it is all physics, though not so simple as human 'logic' tends to make it. First is to realize the bridge is only one of several parts of the system, and all the parts have to work together. Alan Carruth stated that "it's not rocket science, it's actually more complicated". I'm sure he said this in jest but the whole guitar is a very complicated system to understand from a physics perspective. I wish there were simple answers to give you, but keep in mind nothing is perfect and any bridge design will work to some degree, some designs better than others. I prefer the full contact base for the bridge for reasons I have already stated, and adjustable saddles for ease of use (and they work well).

[Beate Ritzert]

That's why i am trying to figure something on the physical background of violin and cello bridges and trying to incorporate this into a few prototypes.
Meanwhile i am a bit curious (again; i had been already while i built the guitar). A few days I have prepared and cut in a prototype bridge from a 10 mm thick slice of Katalox. Even while still in rawly sawn shape it sounds pretty good, better than the old bridge - but not quite as loud. I already seem to have successfully compensated for the asymmetry of the guitar, and have the impression, that it might require a pretty hevy bridge. A nice first result.
As it should be easy to reproduce that (i have enough wood for some more bridges), i dare to convert it stepwise toward a concept closer resembling the action of forces in violin like bridges.

Of course i will remain skeptical and go back if needed.

And yes, You are right: I should and will be carful if i reduce the contact area below the current area.

[Beate Ritzert]

Quick addition, just for the curious: after cutting the bridge into something more violin like i ended up with a louder yet somewhat brighter tone, the latter being in contrast to Red Henry's statement but nevertheless plausible.

I could improve that a bit by positioning the bridge a bit toward the bass side. As this bridge is a usable one - actually better than the old adjustable bridge - it appears meaningful to me to finish it and possibly build another prototype. But not before giving the system enough time to settle.

[Michael Lewis]

Violin bridges function somewhat differently than guitar bridges in that they stand over a sound post by the treble foot, and they are driven with the bow, which imparts a more or less constant input of energy, unlike a guitar that is sounded with a plectrum or fingers, and situated over a "floating" soundboard. There will be some strong similarities between the function of the bridges, but these differences need to be considered in the function and design. Again, I look to tradition for inspiration and ideas, then try something a little different to find if there can be an improvement.

[Beate Ritzert]

That's more or less the same i am doing. I started with a concept of a Maccaferri-Type bridge which is actually used on archtops (Stephan Hahl, Germany) and modified that in a certain direction. I noticed some limitations of that idea (working well on the treble side but not so well on the bass side) and now go one step backward. All within one single prototype. During these experiments i have learned a lot on the possibilities of that specific soundbox and on the degree of changes to be expected by experiments with the bridge - lesser than advertised by Red Henry for his mandolin bridges.

BTW: here the current status on my archtop. The guitar has a 16.3" soundbox, V-bracing and a fairly thick top (6 mm on the edges, 9 mm at max.), and it is slightly thinner than usual. Intentionally - i did not want to have too much bass to make amplification easier.

The following two images show the rawly sawn bridge prototype and the final result on my experiments toward optimising it.

Bridge_Violin.jpg (19.95 KiB) Viewed 22306 times

Bridge_Violin.opt.jpg (18.73 KiB) Viewed 22306 times

The prototype shown in the first picture sounds pretty "thin". As already mentionend, this can be improved by blocking the wing on the bass side again. To my own surprise, even further strengthening of the deep registers can be reached by adding more mass to the bass side - and that result shows that also the treble side should be "opened up" a bit, e.g. by mass reduction or opening up or thinning the wing. Which means that i need to think about a 2nd prototype - after finishing the bridge shown here.

Please let me stress that this is to a large degree instrument specific. Nevertheless it demonstrates the influence of more general and per se fairly well known effects which might be explored further.

A final note to the adjustable/non-adjustable discussion: IMO it matters a lot if You build a guitar to sell it to customers with different demands on string spacing and string thickness, if the guitar is new and still has to settle or if it is a s clear as it is with this old instrument with its 30 years under full string load that it does not need an adjustable bridge. I am also aware that such a process of individual tuning of the bridge cannot be done within the pricing limitations of probably all but the high end guitars.

[Steve Senseney]

I have glued a small strip of bone to the top of saddles to improve the durability of the bearing surface (and appearance). I don't know what effect it had on tone specifically.

[Alan Carruth]

Violin and guitar bridges actually work on _very_ different principles. The violin bow drives the string vibration across the top, but to make sound the top has to move up and down, like a loudspeaker. The way they accomplish this is by use of a sound post, which 'nails' the treble foot of the bridge down, converting the bridge into a bellcrank. Now string force across the top of the bridge causes the bass side foot to push the top up and down over the bass bar, which helps spread the motion along the top. Carleen Hutchins used to say that the post actually reduces the efficiency of the violin by about half (I don't know where she got the number), but most of the loss is in parts of the spectrum where you don't want a lot of sound anyway. It does increase the response in the low range. Early fiddles had no post, and only three strings: when they added the post the bass improved enough that they also added the low string. I've removed the posts from a couple of reasonably sturdy violins, and they get thin, nasal, and cutting.

The violin bridge also has a number of resonances of it's own, which cause it to act as a filter between the string and the top. Enlarging the various cutouts, the eyes and the heart, and removing wood under the legs, tends to drop the pitches of particular resonances, and alter the tone of the instrument. We don't usually use these sorts of cutouts on archtop guitar bridges.

My jazz playing friend is firmly of the opinion that the heavier the bridge is the better. I'm not sure I'd accept the extreme version of that, but it does seem to hold within reason. I have to wonder if the added weight is to balance out the very high stiffness of the arch; it takes some 'oomph' to get that thing moving. More mass in the bridge will, of course, cut down on the acoustic power, but it cuts the treble more than the bass. A heavier bridge should give more bass balance, and maybe a 'fatter' tone.

My own experience suggests to me that full contact is better than two feet. An easy way to check that would be to make a full contact bridge, and then put pieces of veneer under the ends to simulate the feet. You could even experiment with different sizes of feet, to see what you preferred. I did ask about this in a 'First Archtop' discussion session at an ASIA meeting once, and the panel, all experienced makers, agreed that full contact was the way to go.

[Beate Ritzert]

I've removed the posts from a couple of reasonably sturdy violins, and they get thin, nasal, and cutting.

Which is what they even do if the post is not placed correctly. BTW: what about a V-braced Archtop with an (additional) post?

Enlarging the various cutouts, the eyes and the heart, and removing wood under the legs, tends to drop the pitches of particular resonances, and alter the tone of the instrument. We don't usually use these sorts of cutouts on archtop guitar bridges.

Despite of that, my prototype is clearly a success - it improves the sound of the guitar compared to the old industrial bridge. So i will eventually finish it before i do another prototype.
I am still observing the development of the instrument with that bridge and i am still learning a bit: the wings, especially on the treble side, increases the attack/peak responsiveness, but it shortens the sustain. Not too good if the instrument shall also be played electric. I also have the impression that the guitar sounds a bit fuller if the bridge is placed further apart from the neck as it was the case in the raw version before i applied compensation. Mhmm.

More mass in the bridge will, of course, cut down on the acoustic power, but it cuts the treble more than the bass. A heavier bridge should give more bass balance, and maybe a 'fatter' tone.

For my next prototype i am considering a larger thickness in the bass side (but not on the treble side) and again starting full contact. Maybe do another variant with twoo feet.) But anyway in the current prototype the two feet bridge clearly yields more acoustic power than its full contact early version. Which, of course, tells us not too much about other, different, prototypes. I would not be surprised if the demands for acoustic and electric playing differ.

Anyway - thanks for Your input and for the effort of discussion these issues in the meeting. I'll surely learn a lot, especially on the 2nd prototype (which i will probably do in forthcoming spring).


Best

Beate

[Beate Ritzert]

Well, today i finished the prototype. Although i am quite satisfied i will reflect all Your suggestions which i found very helpful. Again a big thank You!


My impression from this experiment is that the potential of the instrument still has not been reached, although i obtained a singificant improvement.

Bridge_Violin.final.jpg (10.52 KiB) Viewed 21886 times

BTW - here is the guitar itself in the state before i started working on it again, i.e. still with the first bridge.



Among the next steps are repair of the finish (do You notice those many scatches on the sides?) and possibly improve and/or renew the string holder.

[Michael Lewis]

There are so many variable aspects to try it seems nearly impossible to find the best bridge after only a few attempts. I continue to like the full contact foot, and lighter is not always better, so we settle for "pretty good" results sometimes and continue to wonder how improvements might be made.

I applaud your efforts to make improvements.

I have made a pair of bridges for each of several instruments, one usually significantly lighter or some other variation of material or design, and have usually heard only small differences. I did not follow up with extensive trials of variations, but sometimes good enough is good enough, and sometimes we get lucky.

[Dave Stewart]

I agree with Michael...lots going on, just within the realm of the bridge (not to mention everything else going on). This is one I'm playing in the white for several weeks to see how things settle. Rosewood, full contact, with a fairly large footprint, but fairly light (27g) and with a bone saddle & no adjustment. I'm really impressed with the acoustic power this thing delivers, although there's certainly contribution from other areas of the design. At some point, I'll have to fit a regular style bridge & try to quantify (or at least perceive) the difference.

[Michael Lewis]

Dave, stimulate the guitar with sound, vibration, flexing, etc. to loosen the structure a bit. These motions are what it needs to go through as it develops a voice, and usually it requires several years to fully develop but with the controlled stimulation it can be hastened significantly so you can hear a distinct improvement within a week. Roger Siminoff offers a "de-damping service" where he subjects the instrument to various forms of vibrational and flexing input to reduce the internal damping of the materials and structure. It works, but you can do much the same at home if you are clever.

There are mechanical devices on the market to accomplish the "playing in" process that can effectively develop your instrument's voice in a few days, if the instrument is capable and willing. You can't make a silk purse from a sow's ear, you know.

[Dave Stewart]

Thanks Michael. I completely agree the most noticeable change happens in the first week, but it will continue to evolve with time. Aside from just playing it, I'll usually run an "aquarium pump" version (see pic) of a Tonerite for several days and am one who believes this helps. (There seems to be 2 camps on this... those that don't feel it works but haven't tried it, and those that have tried it and do feel it works.)
In this case, with the non-adjustable bridge (currently set high), I'd like things to settle before reducing the action.
I'm curious about other techniques involved in the "de-damping" service if you have details.

[Michael Lewis]

I think your assessment of the two camps is correct.

Regarding de-damping, I can only guess at the actual internal process of the changes in the structure but basically you cause it to flex and vibrate until it behaves more like an instrument than a tree. Obviously one should be gentle with the instrument, but still put enough energy into it to cause it to make changes in stiffness and flexibility of critical areas. Machines have been made to stroke the strings with a pick for hours on end, blast sound waves at instruments, and shake them violently with small amount of motion. The latter was done with a "shaker table", much like a giant speaker coil without the cone. You can ask Rick Turner for details, as he was involved in the process as an experimental idea. I don't know of anyone doing that today, and just setting a guitar in front of speakers and playing music through them will help. More volume makes for more significant and quicker results.

[Jason Rodgers]

Dave, that's a clever little setup. How is the guitar held during the process? In a cradle, or just in the case?