# Instruments and Equipment > Builders and Repair >  4 Bridge System Madness.

## Pete Jenner

Kevlar body armour donned and securely fastened, I sit  prepared for the ridicule, derision and ignominy that will doubtless ensue from this thread.  :Coffee: 

Some months ago I bought some cello tuning pegs from my local music shop and ordered some thumb wheel sets from Stewart MacDonald for the purpose of making these adjustable bridge posts.



This is an idea that has been brewing for about four years. Initially I thought it would be an interesting way of reducing crosstalk or phase additions and subtractions in the bridge. A respected scientist/luthier who is a member of these forums informed me that phase interactions in bridges is not significant enough to warrant such an exercise.

Not one to be easily deterred, I kept developing the idea with a different set of objectives in mind. 

The driving motivation is simple curiosity. I want to see if this system results in timbral differences or changes the amplitude of an instrument compared to a 'normal' (in this case a Brekke) bridge. 

Along the way, I'm hoping to dispel a few myths. A lot has been said about mandolin bridges over the years and I believe much of it is complete bunkum. For example, people talk about the tonal and timbral effects of 'wings' and strategically drilled holes placed in certain relationships to the string pairs.

If this system results in a mandolin that sounds and behaves no differently from one with a normal bridge, I think we can discount many of the popular misconceptions regarding bridges.

The mandolin I chose for this experiment is my No. 2 'The Heretic'. A mandolin that many people here have heard and/or played in real life and can attest that it's a fine sounding instrument.

One of the things that has held up this experiment is my belief that I needed to build a special 'non-string gathering' tailpiece in order that the lateral forces didn't pull the posts over. Yesterday it occurred to me that a simple string spreader would do the same job. ....well I was sort of right.

INFO: Each bridge post in this system weighs *3 grams* for a total system weight of *12 grams*. The original bridge weighs *17 grams*.

_More to come (I have to go to bed and change computers)..._

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Bob Clark, 

Dobe, 

Ivan Kelsall, 

j. condino, 

John MacPhee, 

Magnus Geijer, 

Marty Jacobson, 

Michael Lewis, 

Rob Zamites, 

Rush Burkhardt, 

sgrexa, 

SincereCorgi, 

tom.gibson

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## Timbofood

Hmmmm.
Interesting, glad you are fishing this hole Peter, way too deep for me!
Have fun and put on the popcorn!

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## sblock

VERY interesting experiment.  We all (well, at least some of us!) await your findings with bated breath.  Please realize, though, that the added mass of the wooden "string spreader" you introduced between your new, separate bridge posts and the existing tailpiece will certainly affect the mandolin sound.  What does this additional part weigh?  To a good approximation, its extra mass can be expected to add a bit of extra sustain to the sound, just as a mute (usu. placed on or behind the bridge) would, and it may also 'roll off' some of the higher frequencies.

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## Steve Sorensen

And . . . ?  What are your initial impressions of the Heretic 2x4?

Steve

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## Atlanta Mando Mike

Really cool experiment.  I'm very interested to hear how it turns out.  Another idea, and what would be cool to me-a player with absolutely zero ability in the lutherie department, would be to take your idea and attach it to a fixed base so that it would be easy to adjust the action of each string course separately.

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## Pete Jenner

> VERY interesting experiment.  We all (well, at least some of us!) await your findings with bated breath.  Please realize, though, that the added mass of the wooden "string spreader" you introduced between your new, separate bridge posts and the existing tailpiece will certainly affect the mandolin sound.  What does this additional part weigh?  To a good approximation, its extra mass can be expected to add a bit of extra sustain to the sound, just as a mute (usu. placed on or behind the bridge) would, and it may also 'roll off' some of the higher frequencies.


Interesting you should say that Steven, the mass wasn't a factor but the spreader caused big problems.

When I first strung it up and played it, I was going to give the whole thing up as a bad joke. The mandolin sounded like a cross between a banjo and a violin being played pizzicato. It was dreadful, there were strange screechy overtones on every string but especially on the Es and Gs and nearly no sustain at all. 

At first I thought it was the bridge posts but thinking about it more carefully, I realised it was the string spreader. The was no secure anchoring of the ends of the strings so I blocked up the ends of the spreader with some small blocks of wood and voila ...it sustain returned and banjo/violin sounds vanished. It sound pretty normal and not half bad. I still need to make or have made a special tailpiece but until then, all the tests I do with the Brekke bridge will also use the string spreader.



Every test will be recorded and if anyone has good ideas about what tests I should perfom, I'd be glad to hear them.

Apart from the mandolin, the 4 bridge system and the Brekke bridge, the equipment I shall be using is: A Shure 55SH MkII dynamic microphone even though I would prefer a condenser mic but I don't have one. A Digidesign Mbox2, Audacity for FFT analysis and 64 bit Cubase 7 elements for other more musical recordings running on Windows 7.

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gtani7

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## Timbofood

Mind of like Mike's solid base idea, might that help more than the spreader set up?
Mass of the spreader? How much contact with the "feet" on the spreader? Does that add up to contact size of a "single bridge foot"?
This is the kind of thing that really makes me happy to be a member! The ideas, both forward thinking and historically directed are just fascinating.
The little grey cells are having a field day!
Thanks Peter!

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Pete Jenner

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## Pete Jenner

I've thought about that Tim but I'd be concerned that it would add too much mass and restrict the ability to adjust the intonation on each pair separately.

The spreader is about 2 grams. If I get good results, I'll get rid of the spreader and use a non-string gathering tailpiece.

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## sblock

> Interesting you should say that Sean (Shaun?), the mass wasn't a factor but the spreader caused big problems.
> 
> When I first strung it up and played it, I was going to give the whole thing up as a bad joke. The mandolin sounded like a cross between a banjo and a violin being played pizzicato. It was dreadful, there were strange screechy overtones on every string but especially on the Es and Gs and nearly no sustain at all. 
> 
> At first I thought it was the bridge posts but thinking about it more carefully, I realised it was the string spreader. The was no secure anchoring of the ends of the strings so I blocked up the ends of the spreader with some small blocks of wood and voila ...it sustain returned and banjo/violin sounds vanished. It sound pretty normal and not half bad. I still need to make or have made a special tailpiece but until then, all the tests I do with the Brekke bridge will also use the string spreader.
> 
> 
> 
> Every test will be recorded and if anyone has good ideas about what tests I should perfom, I'd be glad to hear them.
> ...


Hi there. Actually, my first name is Steven, not Sean.  But no matter!

In your modified setup, the string spreader has sprouted two "feet" that contact the mandolin top directly.  These can be expected to act as a kind of auxiliary (secondary) bridge, because any vibrations of the strings and 4 bridge posts will be communicated (although somewhat damped) right back to the spreader, and then down onto the top.  My instincts are telling me that this experiment will not, therefore, offer a clean way to learn what you're trying to learn:  namely, whether 4 separate string posts that inividually contact the top can replace, or improve upon, a single bridge with a saddle that either has two feet or is full-contact. You will get some results, of course, but these will be darned hard to interpret.  Can't you figure a way to get rid of the top-supported spreader?  Are you absolutely SURE you need it -- the four posts that you made, if fitted closely to the top, might just resist the lateral string forces perfectly well (given the high downbearing forces on the top and all that associated friction), and eliminate the need for a spreader.  Regardless, I think you need to find a clever way to do this experiment without added additional elements that vibrate the mandolin top.  But keep up the work!

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camog, 

Pete Jenner, 

Timbofood

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## Pete Jenner

Ah sorry Steven. I could have sworn I've seen you sign your name Sean in the past. I think I'm getting old timers disease. I just edited my post accordingly.

Yes I agree that the spreader is less than ideal but it shouldn't act as a bridge because the string vibrations all occur between the bridge and zero fret and the spreader is a long way back. This experiment will be ongoing and will eventually be done without the spreader.

I tried the posts without the spreader and while the G and E posts don't fall over under full string tension, the do tilt a bit. That's why I need to get a wide tail piece. I'd be interested to hear from anyone who can tell me how to make one.

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## Timbofood

What about a spreader between the adjuster posts, sort of a strap with holes for maintaining the interval?

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Michael Lewis

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## Pete Jenner

I'd rather keep them completely separate but I understand where you are coming from.

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## sblock

I certainly don't mean to sound argumentative -- and I mean to encourage your experiment! -- but I believe that you are wrong about the spreader-with-feet not acting as a secondary bridge. 

The tension in the strings causes them to bear down on the main bridge (usually through the saddle, or in your case, through 4 separate saddles), and after the strings are sent into vibration by the energy introduced by the pick, some of that vibration, and energy, is transmitted through the bridge and down into the top.  _But not all of it_.  Quite a bit of the remaining vibrational energy travels rearward, beyond the bridge saddle, and towards the tailpiece. In fact, that is the reason that many mandolinists use rubber grommet dampers, Weber "wood nymphs", or bits of felt or leather to dampen these vibrations, which can cause parasitic, unwanted sounds.  And this same vibrational energy is also what causes loose tailpiece covers to rattle!  So, it is a significant amount of energy.  In your current setup, you are coupling the vibrational energy of the strings behind the bridge to the mandolin top through the feet of the string spreader.   It will definitely act as a secondary bridge. Whether it turns out to be a small or a large perturbation, over-and-above the primary bridge, remains to be determined, but an effect is to be expected.  Also, by bearing down, the two feet of the spreader will tend to produce a NODE line (a line of zero vibrational amplitude) in the complex modes of vibration of the top, thereby suppressing any of the (many) vibrational modes that happen to have high amplitude under the location of the spreader feet. (This is equally true of the regular mandolin bridge, which is one of the reasons why Lloyd Loar moved the F5 bridge more towards the center of the top, by lengthening the portion of the neck before it reached the body to 15 frets, compared to the earlier, shorter-neck F4).  That will also change the sound, for sure.

Anyway, theory only tells us so much.  You have to do the experiments!  But, I hope you agree, these need to be "cleanly designed" to test what you think you really want to test -- and not something else.  If you want to test the effect of 4 separate bridge saddles instead of just 1 common saddle, you ought not (1) mass-load and dampen the strings behind the bridge position with a spreader, and (2) have that spreader transmit vibrations to the top.  It's still an interesting sonic experiment as you have it, of course, but I would not know how to interpret the results.  Any change in sound or timbre  _could_ be due to the separate saddles, but it could equally well be be caused by the spreader. Or both!  You will be left with a mystery. You want to design your experiment to change as few things at a time as possible.

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## Pete Jenner

Argument is good. Thanks for taking an interest. I'll read your post properly when I wake up and give it some proper thought.

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## Jacob

The mandolin equivalent of a banjo straight pull tailpiece might help.

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## Pete Jenner

> The mandolin equivalent of a banjo straight pull tailpiece might help.


Yes. That's what I need Jacob.

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## fscotte

I'm a firm believer that current bridge technology is as good as it gets.  There's only a few things that a bridge has to do, and the current Loar bridge does em all.  But still, I like to see your results.

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## sblock

By contrast, I'm a firm believer that there's nearly ALWAYS some room for improvement when it comes to acoustic instrument design.  How much room?  It depends!  Modern violins are now being built that are acoustically indistinguishable from Golden Age Cremona violins made by Stradivari and Guarneri -- even by some of the very best virtuoso violinists. So there are no "secrets" to these that cannot be replicated or even surpassed, it seems.  Luthiery is a process, not an end-point!

Anyway, there is *a whole lot* not to like about the Loar-era mandolin bridge design! The saddle is known to be imperfectly compensated. Its shape also weakens it, and it is subject to breaking easily (many broken saddles). The two bridge feet on the base do not make optimal contact with the top (which is why some have elected to get full-contact bridge bases, instead), and the actual contact area of the two-foot base changes quite a bit from instrument to instrument, due to the need for sanding and fitting to the top. The bridge saddle cannot easily be adjusted for height under full string tension, as we all know.  Bridge saddles, especially those that have to be raised higher than normal, tend to tilt progressively more forward under string tension or with string changes.  The tone of the bridge seems to vary a lot with the woods used, so it's not all that reproducible.  Strings can get easily stuck in the slots.  And on and on -- that's just a short list of SOME of the shortcomings of the Loar-era two-piece design.  

That said, it still might be the best design out there at the moment. It's like what Winston Churchill said about democracy: "It's the worst form of government, except when you consider all the rest!" 

But that doesn't mean one can't do better in bridge design!

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camog

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## fscotte

I guess it depends on what some consider an improvement.  If I had a special bridge that added a dramatic amount of sustain, the knee jerk reaction would be how great that is.  But on second thought, more sustain isn't generally a good idea for a loar style mandolin.  The things you mention above aren't necessarily the shortcomings of a two footed bridge, but rather sloppy work by the builder.  Solid contact from the feet and the top can be achieved with patience.

I've yet to see an "improvement" in bridges.  There's been a whole assortment of experiments for many years.  But the job of a bridge is very basic, there isn't anything magical about what it does.

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## sblock

> I guess it depends on what some consider an improvement.  If I had a special bridge that added a dramatic amount of sustain, the knee jerk reaction would be how great that is.  But on second thought, more sustain isn't generally a good idea for a loar style mandolin.  The things you mention above aren't necessarily the shortcomings of a two footed bridge, but rather sloppy work by the builder.  Solid contact from the feet and the top can be achieved with patience.
> 
> I've yet to see an "improvement" in bridges.  There's been a whole assortment of experiments for many years.  But the job of a bridge is very basic, there isn't anything magical about what it does.


Well, I entirely agree that there's nothing really magical about what the bridge does! And I'd be inclined to agree that the assortments of experiments that have been done have not necessarily led, yet, to a "better" bridge than the Loar-era two-foot design.  At least not one that's widely embraced by the mandolin community.  But then, popularity/widespread acceptance by this community (which tends to be VERY conservative about design, for better or worse!) is not perhaps the right measure for whether one design is "better" than any other.  Still, we've had some pretty nice  -- and fine-sounding -- alternatives tried, like the Vern Brekke adjustable (wood cam) bridge, and also the Weber "Traditional" bridge, which has a metal crossbar under the saddle, and can be adjusted under full string tension.  But these bridges are not all _that_ widely accepted, nor -- to my ear -- do they sound noticeably better, so they have not displaced the bridges with the traditional Loar-era designs.  I also agree with you that it depends, to a great extent, on exactly what one means by "improvement." Amen to that.

The only part of your response that I'd quibble with is where you wrote this: "_The things you mention above aren't necessarily the shortcomings of a two footed bridge, but rather sloppy work by the builder._"  Sorry, but I disagree completely with that! For example: (1) the inability to adjust the bridge height under full string tension is an intrinsic _design drawback_ of the Loar-era bridge, and not evidence of sloppy work.  (2) The fact that mandolin tops all have slightly different shapes, and therefore that the _contact area of the two-foot bridge_, which must be sanded and fitted to each and every top, is different from one mandolin to the next, is not a result of sloppy work, either!  (3) The imperfections in the compensation of the saddle (which also vary with the choice of string gauge) are also not evidence of sloppy work -- they are intrinsic to the shape of the saddle (and vary slightly with different makers of bridges, too).  (4) Also, the tendency of the saddle to lean progressively forward, especially when the thumbwheels have to be raised to a high position on some mandolins, is also a design flaw of this type of bridge, and not a product of sloppy work.   So no, these shortcoming are NOT sloppy work: they are inherent flaws with the design, and they have been recognized as such (repeatedly) on this forum, and by individual luthiers.

That said, the Loar-era two-foot design with thumbwheels works in most cases, and it gives many of us the sound we enjoy.  But it's also a source of many headaches for mandolinists and luthiers alike, and a better-sounding and better-adjusting alternative would be great to have.  

To cite an analogous example of progress in design: I think the Bill James version of the mandolin tailpiece, with its hinged cover and integral noise dampers and solid attachment posts, represents a HUGE improvement over the earlier Loar-era design, with its flimsy stamped parts, separate cover (that rattles, comes loose, gets lost, etc.) and fragile, punched string posts (that break, cut into the strings, and so on).  Yes, the James tailpiece LOOKS just about the same, from afar, and it SOUNDS just about the same (maybe even better?), but it's -- hands-down -- _a better design_!!  And just look at how many of the really top-end, single-luthier mandolins are featuring James tailpieces. Or one-piece tailpieces, of the type first pioneered by John Monteleone (e.g. the Allen tailpiece). These are all improvements over the 2-piece Gibson tailpiece design, IMHO.

I'm just waiting for someone to do something similar with the mandolin bridge. Yes, there is ample room for design improvement, folks.  And yes, the mandolin of tomorrow will be better than the mandolin of today. Mark my words.  We're not done improving the mandolin.

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Pete Jenner, 

Rob Zamites

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## j. condino

"Kevlar body armour donned and securely fastened, I sit  prepared for the ridicule, derision and ignominy that will doubtless ensue from this thread....."

Quite possibly the most insightful thing ever stated here!!!!

Peter, good on ya' for the creativity and curiosity and even bolder for wilingness to stand naked and post it around here; keep it up! As for the crusty crusty whole lotta nuthin' nay sayers....a simple two word phrase comes to mind..... :Wink: 

j.
www.condino.com

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Austin Clark, 

Michael Lewis, 

Pete Jenner

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## Tom Haywood

Pete, I am very interested to hear the outcome of this experiment. My two pennies: If this weren't an iconic mandolin, you could tap some small nails into the end for loop holders to accomplish the straight pull. I think with the spreader you have in effect split a normal bridge into two locations touching the top, and that will not present the data you wish to test. Also, with the four posts you have, in effect, doubled the number of metal posts found in a standard adjustable bridge. I am interested to see if this causes any differences in the transmission of the overall string vibrations to the top. I agree with Mike that you may be onto something with the ability to easily adjust string height and intonation individually (shades of setting up electric guitars). You may have to design the mandolin tailpiece for this.

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## Timbofood

OK Peter, you have strung this rascal up, what does your ear tell you? First impression?

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## Steve Lavelle

It seems to me that one function of the traditional bridge is more even distribution of the significant downward pressure across the top plate. With the 4 independent supports in this experiment, what is the area of each bridge piece base? It looks like there may significantly more pounds per square inch at each of the contact points, making the top more susceptible to cracking or sinking in the long run.

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## fscotte

You would lose the normal rocking motion that a traditional bridge applies to the top plate.  BTW, bridges don't transmit vibrations to the top.  The bridge acts as a lever, more of a mechanical force, not like electricity.

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## dan in va

+1 to Skunkwood's comment.  David Grisman's F5 had the bridge base bobbed back in the mid 1970's, and later he went back to the original long style....i wonder why.  There have been numerous testimonies of tops sinking under 2 footed bases and not affecting the middle section, and full contact bridge bases solved the issue.

Good on y'all if it works.  However, the old style long base seems to reach the tone bars and distribute the force over more of the top -- a full contact bridge even more.  So for a short bridge to work on traditionally designed tops, will something need to be changed to make the shorties work long term?

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camog

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## David Houchens

IIRC, John Hamletts Tail pieces were near in-line with a standard bridge spacing.

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Pete Jenner

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## Pete Jenner

> I certainly don't mean to sound argumentative -- and I mean to encourage your experiment! -- but I believe that you are wrong about the spreader-with-feet not acting as a secondary bridge. 
> 
> The tension in the strings causes them to bear down on the main bridge (usually through the saddle, or in your case, through 4 separate saddles), and after the strings are sent into vibration by the energy introduced by the pick, some of that vibration, and energy, is transmitted through the bridge and down into the top.  _But not all of it_.  Quite a bit of the remaining vibrational energy travels rearward, beyond the bridge saddle, and towards the tailpiece. In fact, that is the reason that many mandolinists use rubber grommet dampers, Weber "wood nymphs", or bits of felt or leather to dampen these vibrations, which can cause parasitic, unwanted sounds.  And this same vibrational energy is also what causes loose tailpiece covers to rattle!  So, it is a significant amount of energy.  In your current setup, you are coupling the vibrational energy of the strings behind the bridge to the mandolin top through the feet of the string spreader.   It will definitely act as a secondary bridge. Whether it turns out to be a small or a large perturbation, over-and-above the primary bridge, remains to be determined, but an effect is to be expected.  Also, by bearing down, the two feet of the spreader will tend to produce a NODE line (a line of zero vibrational amplitude) in the complex modes of vibration of the top, thereby suppressing any of the (many) vibrational modes that happen to have high amplitude under the location of the spreader feet. (This is equally true of the regular mandolin bridge, which is one of the reasons why Lloyd Loar moved the F5 bridge more towards the center of the top, by lengthening the portion of the neck before it reached the body to 15 frets, compared to the earlier, shorter-neck F4).  That will also change the sound, for sure.
> 
> Anyway, theory only tells us so much.  You have to do the experiments!  But, I hope you agree, these need to be "cleanly designed" to test what you think you really want to test -- and not something else.  If you want to test the effect of 4 separate bridge saddles instead of just 1 common saddle, you ought not (1) mass-load and dampen the strings behind the bridge position with a spreader, and (2) have that spreader transmit vibrations to the top.  It's still an interesting sonic experiment as you have it, of course, but I would not know how to interpret the results.  Any change in sound or timbre  _could_ be due to the separate saddles, but it could equally well be be caused by the spreader. Or both!  You will be left with a mystery. You want to design your experiment to change as few things at a time as possible.


Yes I do agree the spreader is not a great idea but will have to remain until I have an alternative. I don't think it will establish nodes or node lines any more than a planted piny or resting arm would. The downwards pressure on the blocks from the strings at that point is only sufficient to immobilise the spreader and that is one of the thicker parts of the top. But it is all speculation on my part and the goal remains to replace the spreader with a better solution.

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## Pete Jenner

> IIRC, John Hamletts Tail pieces were near in-line with a standard bridge spacing.


Maybe he'll be willing to sell me one if that's the case.

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## Pete Jenner

> "Kevlar body armour donned and securely fastened, I sit  prepared for the ridicule, derision and ignominy that will doubtless ensue from this thread....."
> 
> Quite possibly the most insightful thing ever stated here!!!!
> 
> Peter, good on ya' for the creativity and curiosity and even bolder for wilingness to stand naked and post it around here; keep it up! As for the crusty crusty whole lotta nuthin' nay sayers....a simple two word phrase comes to mind.....
> 
> j.
> www.condino.com


Thanks James.

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## Pete Jenner

> OK Peter, you have strung this rascal up, what does your ear tell you? First impression?


Initial impression is that it doesn't sound too different from the standard 2 footed bridge but I'll start taking some measurements this afternoon or tonight.

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## Pete Jenner

Just a as a general note on this exercise, it is not designed to take over from or make the standard bridge designs redundant.
I'm just trying to shed a bit more light on bridges and explore possibilities. If it turns out this system has a place in the world of mandolin bridges, that's great. If not, that's fine too.

One thing I have discovered is that the thumb wheels on the D and A strings are nearly impossible to access. Eventually they will be will replaced by hex nuts like the ones used in Marty Jacobson's bridges.

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David Houchens, 

Timbofood

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## Pete Jenner

> +1 to Skunkwood's comment.  David Grisman's F5 had the bridge base bobbed back in the mid 1970's, and later he went back to the original long style....i wonder why.  There have been numerous testimonies of tops sinking under 2 footed bases and not affecting the middle section, and full contact bridge bases solved the issue.
> 
> Good on y'all if it works.  However, the old style long base seems to reach the tone bars and distribute the force over more of the top -- a full contact bridge even more.  So for a short bridge to work on traditionally designed tops, will something need to be changed to make the shorties work long term?


The 'Heretic' is X braced with the X crossing not far in front of the bridge position.

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## Marty Jacobson

> You would lose the normal rocking motion that a traditional bridge applies to the top plate.  BTW, bridges don't transmit vibrations to the top.  The bridge acts as a lever, more of a mechanical force, not like electricity.


Why do you think that? Just curious.

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## dan in va

Pete, the X braced top seems like a good idea with your bridge idea.  It wouldn't be hard to add a little brace under the bridge if any sagging started.  Thanks for the update, and i hope you'll revisit the thread over time.

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## Bertram Henze

The good thing I see there is decoupling of transversal guidance from vertical and longitudinal adjustment, like in a nut/zero fret combination. 
I am not sure about the decoupling of courses from each other, though: what happens to overtone injection? Does the high D (A strings 5th fret) still make the open G strings ring along as strong as it used to? The camps are divided in how that would be a good or a bad thing, but I for once would miss the richness in overtones.
Also, I am not sure about busting common myths - for each myth busted there will be two new ones created. But that's a welcome enhancement in oncoming Cafe discussions on the "Jenner 4 cylinder engine"  :Wink:

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Marty Jacobson, 

Pete Jenner

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## Pete Jenner

I think you may have a point about the de-coupling adversely affecting overtones Bertram.  I put the original bridge back on with the string spreader in place and there was a very noticeable improvement in the sound.

So... I've come up with a way to couple the posts below the thumb wheels and still allow them to be adjusted forwards and backwards. This will probably take me all night so bear with me.

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## Michael Lewis

Pete, I think your idea can benefit from side to side stability.  If you elongate the feet for each bridge to give that stability the feet will have to run past each other.  If you angle them slightly they will form a continuous contact base of bypassing pieces.  Diamond shaped feet would form a single "foot" of four pieces.  Imagine smooth straight edges along the base front and back, with diagonal lines showing the edges of the individual feet.  I don't have a thousand words.

Also, you state the separate pieces together weigh less than the original style bridge.  I think you may get better sound with a bit more weight, but experimenting will show you what works best.  It may well prove that different weights work best for different strings (frequencies).

Though this design will be a bit more fiddly and have more pieces than the standard design it may well be a superior concept.

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## Pete Jenner

Thanks Michael. It's very useful to get all this input from great builders.

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## Bertram Henze

Don't forget to make recordings of all possible configurations. Don't rely just on memory. I guess we all are looking forward to a big acoustic bridge concept tasting showdown in the end.  :Cool:

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## Pete Jenner

I spent hours trying to get Audacity working with my hardware today and gave up in frustration.

...then I remembered the mic has an off switch. ...stupid bloody off switch ....should be illegal.

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Killian King, 

Timbofood

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## Bertram Henze

> ...then I remembered the mic has an off switch.


Being freaked out with the overlooked obvious is a sure symptom of mental overload and insomnia. Rest is brain's best friend.

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## Pete Jenner

So now that I have audacity working, should I plot the spectra on a logarithmic scale or linear? 
Should I save a text version of the spectrum data or take a screenshot of the graph?

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## Bertram Henze

> So now that I have audacity working, should I plot the spectra on a logarithmic scale or linear? 
> Should I save a text version of the spectrum data or take a screenshot of the graph?


- logarithmic is better
- screenshot is more colorful

But we like to hear it, too!  :Cool:

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Pete Jenner

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## Pete Jenner

I was thinking of just playing single notes on open and fretted strings or should I play some tunes as well? Tunes won't sound great because I only have one E string at the moment - no spares until Monday.

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## Bertram Henze

Single notes are ok (how about one scale over 2 octaves from G to g') and most reproducible, but the courses should be complete. No need to hurry. I'd expect this to be more of a longterm project, no?

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## Pete Jenner

Absolutely. It may go for months ...or years.  :Smile:

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## Michael Bridges

Take your time, Pete! I get this mental picture of yo starting to look like Doc Brown , running around your shop. "To sleep, perchance to dream"

----------

Pete Jenner

----------


## Pete Jenner

> Take your time, Pete! I get this mental picture of yo starting to look like Doc Brown , running around your shop. "To sleep, perchance to dream"


I've got no idea what you're talking about Mike but If my calculations are correct, when this baby hits 88 miles per hour... you're gonna see some serious sh*t.   :Grin:

----------

Marty Jacobson, 

Michael Bridges, 

Timbofood

----------


## fscotte

> but I for once would miss the richness in overtones.


In the piano world, it's called sympathetic resonance, and adds a great deal to the acoustic piano sound.  Thus the reason why so many digital pianos sounds like, er digital.  They try to emulate the resonance, but it's not real.  I think if an instrument is in tune, those resonances is what adds to the complexity of the sound.

----------

camog

----------


## fscotte

> Why do you think that? Just curious.


A short lever would have less control over the top.. would it not?  If you isolate each string on a post about 1/8" wide (if possible without damaging the top) how would that exert more or the same amount of force on the top as a bridge that extends from one side to the other.

Que, Dr. Cohen, but I see this thing as a lever, or better yet, a see saw, nothing more.

----------


## Timbofood

This is going to be fun!

----------


## fscotte

Pete, you could also superglue the posts to the top and possibly forego the crossbrace?

----------


## Timbofood

I was thinking something like the links on a bicycle chain thin plates with a hole in each end just heavy enough to keep thing from slipping toward the center.  If this makes a billion dollars, it was my idea for that! :Laughing:

----------


## Marty Jacobson

> A short lever would have less control over the top.. would it not?  If you isolate each string on a post about 1/8" wide (if possible without damaging the top) how would that exert more or the same amount of force on the top as a bridge that extends from one side to the other.
> 
> Que, Dr. Cohen, but I see this thing as a lever, or better yet, a see saw, nothing more.


Interesting, thanks. To clarify, which direction do you think the forces are acting in? The width of the bridge, or the thickness of the bridge?
An easy way to test this (besides some quick free body diagrams for sanity checking) is to make a 50% wider than normal bridge in whichever direction is appropriate. I have done wider bridges (s-shaped like Weber mandola bridges designed by Vern Brekke), but not especially long bridges.

----------


## fscotte

Dave can certainly clarify the motion of bridges.  Rocking sideways, forwards?  Maybe another motion as well.  

There's some videos of strings in slow motion and they have this whipping motion, stabilized at the bridge and the nut.  In minute terms that's really kicking the bridge around, a mechanical force.  But it's not really just the bridge, it's the entire top.  The bridge makes solid contact with the top, so it is one entity.  You could essentially carve a bridge out of the top plate.. if it were possible.

I think you've read Dave's papers and posts, so he will correct any issues, but that's my take on it, no matter how scientific or unscientific it may be.



For Pete's bridge to work, he'll need to forego the crosspiece somehow, otherwise he's just making a Loar bridge more complex by adding two extra feet and a crosspiece that isn't connected to the feet.

----------


## Rick Lindstrom

"Modern" mandolin design reached its zenith with Bill Monroe and the Loar F5. It's pretty obvious that anything different from the standards it set won't work. Give it up Pete.

 :Wink:

----------


## DougC

Going out on a limb here. My first impression is that the strings may need to share overtone frequencies at the string spreader or a regular bridge, where they usually do it. Do they do it within the instrument? To what extent? Hmmmm?

----------


## sblock

> "Modern" mandolin design reached its zenith with Bill Monroe and the Loar F5. It's pretty obvious that anything different from the standards it set won't work. Give it up Pete.


Well, you really had me going until I saw that emoticon winking back at me!  This comment would be more amusing if it weren't for the fact that so many Bluegrass mandolinists actually seem to believe it. Of course, this same type of thinking pervades other musical genres, as well. Onward through the fog, I say!!

----------


## Dale Ludewig

Pete, I think you're beginning to resemble this guy.   :Smile: 



CARRY ON!

----------

Pete Jenner

----------


## Rick Lindstrom

> Well, you really had me going until I saw that emoticon winking back at me!  This comment would be more amusing if it weren't for the fact that so many Bluegrass mandolinists actually seem to believe it. Of course, this same type of thinking pervades other musical genres, as well. Onward through the fog, I say!!


I may have intended a wee tiny morsel of irony with that comment. I mean, after all, everybody is working madly to recreate a design that was new almost a hundred years ago.

I can't think of any real innovations in mandolin technology since time came to a halt in 1924.

----------


## fscotte

Kinda goes for most stringed instruments from guitar to piano.  It's somewhat amazing that the "alleged" pinnacle of acoustic stringed instrument design was achieved so long ago, with only minor and occasional useful tweaks here and there.  In the case of acoustic piano, it's as if they knew what had to be done but simply did not have the technology to build it until the early twentieth century.

----------


## Marty Jacobson

> I can't think of any real innovations in mandolin technology since time came to a halt in 1924.


Whoa, that's a very sweeping statement. Is it hyperbole/litotes? 
If not, what do you consider "innovations"? 

How about some of the following, just off the top of my head:
- Modern varnish finishes
- Radiused & compound radiused fretboards
- Magliari compensated fretboards
- Carbon fiber mandolins
- Carbon fiber neck stiffeners
- More efficient manufacturing techniques (CNC, FFT spectrum analysis, etc.)
- Cast tailpieces, James tailpieces, etc.
- Anything designed by Verne Brekke, especially the Brekke bridges in both wedge-adjust and thumbscrew variants

Lots and lots more... just read through the Big Red Books of American Lutherie and you'll be astonished. I believe every single luthier who has built 10+ instruments has developed useful innovations in the craft. Any many luthiers come up with useful innovations on their very first instrument. It is far from a static set of objectives or processes.

Also, there are many different mandolin voices out there. Every single on of my customers describes something which is a little different. I don't think that there is one single pinnacle of mandolin technology that would satisfy all of them. Even if I could make a Loar sound-alike for $3000, not everybody would choose it.

----------

Bob Clark, 

CeeCee_C, 

JEStanek, 

Pete Jenner, 

Rob Zamites, 

sblock, 

sgrexa

----------


## Killian King

> I've got no idea what you're talking about Mike but If my calculations are correct, when this baby hits 88 miles per hour... you're gonna see some serious sh*t.

----------

Hudmister, 

Michael Bridges, 

Pete Jenner, 

Timbofood

----------


## Bob Clark

> . . . That's why I need to get a wide tail piece. I'd be interested to hear from anyone who can tell me how to make one.


Please forgive me if this idea has already been suggested or if you've solved the tailpiece issue some other way, but how about making a tailpiece like Walt Kuhlman makes for some of his mandolins, but even wider?  If you made one wide enough, the strings would continue in a straight line below the bridge to the tailpiece.  He posted this picture in another thread a while back.  It's of a nylon-strung mandolin I now own, but I thought a tailpiece like this, but even wider, might help your experiments.

----------

Pete Jenner

----------


## Pete Jenner

Yes it would indeed Bob.

----------


## Rick Lindstrom

> Whoa, that's a very sweeping statement. Is it hyperbole/litotes? 
> If not, what do you consider "innovations"? 
> 
> How about some of the following, just off the top of my head:
> - Modern varnish finishes
> - Radiused & compound radiused fretboards
> - Magliari compensated fretboards
> - Carbon fiber mandolins
> - Carbon fiber neck stiffeners
> ...


Pretty much everything you mention is more or less an incremental improvement. Like going from v1.0 to v1.1 or something like that. Some kind of major innovation, which hasn't happened as far as I can tell, would be like going from v1.0 to v2.0. Or like going from Windows XP to Windows 7 if you follow my drift. Apologies to you Mac and Linux users out there.

Carbon fiber mandos almost qualify, but it's still really just the same old design executed in a different medium. As far as voice goes, every mandolin has it's own unique voice. No two are identical, and it's always been that way. Maybe the CF mandolins all sound the same, but I wouldn't know because I've never heard any of those in person. What a shame it would be if they all _did_ sound identical.

----------


## Bertram Henze

> ...Or like going from Windows XP to Windows 7 if you follow my drift. Apologies to you Mac and Linux users out there.


Apology accepted. However, XP to 7 is just an increment to me (wouldn't exactly call "less frequent freezing up" or "looking more like OSX ten years ago" an innovation), and improvement remains a vast untapped potential with Windows...  :Cool: 

A real innovation must enable applications not possible before, like, for instance, the jet engine vs. the propeller.

----------


## Pete Jenner

Windows 7, when properly set up with minimal background processes running is as good as XP. For me it's better because I went from 32 bit to 64 bit thereby allowing me to access all 16 gigs of memory. Windows 8 on the other hand is complete rubbish.

----------


## Rick Lindstrom

> Windows 7, when properly set up with minimal background processes running is as good as XP. For me it's better because I went from 32 bit to 64 bit thereby allowing me to access all 16 gigs of memory. Windows 8 on the other hand is complete rubbish.


I like Windows 7 a lot, but the reason I switched from XP (which did everything I needed just fine) was because Microsoft pulled the plug on it as far as support and updates. I agree that Win8 was probably pretty bad (never used it), but it seems like 8.1 (incremental advance-LOL) addressed a lot of the problems 8 had.

I read somewhere that Microsoft plans to give away Windows 10 free to people that are running registered versions of Win7 and above. That should be interesting.

Actually, I liked Windows 2000 pretty well. When it first appeared, MS intended to call it NT 5.0 (major version update-LOL again), and I'm pretty sure that everything MS has done with Windows since then has been elaboration on the NT 4.0 platform.

The regularly scheduled program of mandolin related content will now resume........

----------


## Pete Jenner

I liked Dos 5, Dos 6.22 and Windows 3.11. Then Windows 2000, XP and 7. ME was rubbish as was Vista, 95 was bad but 98 was better. I upgraded to 7 because my son bought it for me.

No work on the bridge system for a few days - real life intervenes.

----------


## Rob Zamites

I'm an OS X guy. Just call me a heretic, but it works for GUI/Music stuff well, and has a command line back end/*nix framework (I'm a Linux admin).

----------


## sblock

Wow, folks seem to be having trouble staying on topic.  And some of us here are old enough to remember OS's like RSX, RT-11 (both DEC) and CP/M and ZPR3 (for the Z80 chip). Thank the gods for evolution, I say!   :Wink:

----------


## fscotte

DOS 2.1 = Loar
Windows 10 = Pete Jenner

----------

Rob Zamites, 

Timbofood

----------


## Pete Jenner

Haha.

Don't tell anyone but I run Fedora GNU/Linux on my laptop.

----------


## Bertram Henze

> Wow, folks seem to be having trouble staying on topic.  And some of us here are old enough to remember OS's like RSX, RT-11 (both DEC) and CP/M and ZPR3 (for the Z80 chip). Thank the gods for evolution, I say!


I remember RT-11, and nights in front of a PDP. Those days are over, or so I thought, until I had one hell of several nights 20 years later in front of a Windows NT laptop in China. Evolution? Yes, but that should involve extinction.

----------

sblock

----------


## Rick Lindstrom

You Linux folk should try Puppy Linux. It's a very small Linux implementation that loads entirely in RAM (about 100meg) and runs from what I assume is something like a RAM-disk. Because it runs from RAM, it is almost instaneous.

It can be booted from a flash drive, and I start my Windows machine with Puppy when I do online banking or other sensitive stuff.

----------


## Timbofood

I'm so confused! Flashing boots, puppies out windows, where is Linus's blanket when you need it!

----------

Mandocarver

----------


## des

> Pretty much everything you mention is more or less an incremental improvement. Like going from v1.0 to v1.1 or something like that. Some kind of major innovation, which hasn't happened as far as I can tell, would be like going from v1.0 to v2.0. Or like going from Windows XP to Windows 7 if you follow my drift. Apologies to you Mac and Linux users out there.
> 
> Carbon fiber mandos almost qualify, but it's still really just the same old design executed in a different medium. As far as voice goes, every mandolin has it's own unique voice. No two are identical, and it's always been that way. Maybe the CF mandolins all sound the same, but I wouldn't know because I've never heard any of those in person. What a shame it would be if they all _did_ sound identical.


Do you think Brian Dean's work qualifies ? Lots of info here -    http://www.josephbrent.com/mandolins/

----------


## David Houchens

Heres a shaot of a Hamlett tail piece. Never seen masking tape used to dampen the strings between bridge and tailpiece. Dead on inline with bridge.

----------


## Rick Lindstrom

> Do you think Brian Dean's work qualifies ? Lots of info here -    http://www.josephbrent.com/mandolins/


That's some beautiful work- thanks for pointing Brian out to me.

Guess we gotta split hairs on this discussion. What I probably meant to suggest by the term "innovation" is a design that eclipsed the F5 design and sidelined it the same way that the F5 has done to other designs. I know that A models are popular, but they are scorned by the bluegrassers that make up the (apparent) majority mandolin market nowadays. I know this is simplifying things, but readers  of this forum probably know what I mean. F5 mandolins are what "everyone" wants and what a lot of builders spend most of their time building. I'm not in any way blaming the builders- they're building what the market demands.

Also, it may just be an American phenomenon because the US is the home of Bill Monroe. I know that bluegrass is quite popular in Europe, but I wouldn't expect the F5 to dominate so completely there because Europe is the home of classical music. The rest of the world? Who knows. I bet there are plenty of countries where people have never heard of bluegrass music.

PS- I'm really interested in finding out how Pete's 4 bridge trials go, and I'm sorry to have hijacked this thread- my apologies to Pete.

How's it going with your new bridge design Pete?

----------


## Bertram Henze

> ...it may just be an American phenomenon because the US is the home of Bill Monroe.


In single cases, the reasons may be completely different ones. Blessed with a Freudian violin trauma in my youth, I approve of an instrument that is openly making fun of the violin's stylistic elements, and I always feel better when I see one. It is not neccessary to actually own one, though - just seeing it at regular intervals will suffice for me.  :Cool:

----------


## Tobin

> Heres a shaot of a Hamlett tail piece. Never seen masking tape used to dampen the strings between bridge and tailpiece. Dead on inline with bridge.


I've been following this thread with interest and curiosity.  One thing that occurs to me as I look at the photo is that even if a tailpiece were to spread the strings out to the spacing one desires at the bridge, the strings still have to converge a bit as they approach the nut.  So the 4 separate bridge posts would still have some degree of side-loading on them, as it would be impossible to put a spreader between the bridge posts and the nut.  One would hope that the bridge posts would be stable enough to resist slipping or vibrating towards each other over time due to this constant lateral force.  But I would suspect that over time, the spacing between courses would change as the bridge posts try to slowly walk their way towards being in-line between the tailpiece connection points and the nut slots.

The only way to fix this would be to have an even wider tailpiece that doesn't just spread the strings out to normal bridge spacing, but that spreads them out even wider so that the strings are at the correct bridge spacing _where they cross the bridge posts_, and flaring slightly wider by the time they reach the tailpiece.

----------

camog

----------


## Timbofood

Now, you see what you have done Peter!?

----------


## fscotte

Superglue.

The second time I've mentioned this.  Amazing stuff.

----------


## Marty Jacobson

I've been trying to remember what this bridge system reminded me of. Eureka -- Koto.


Tobin, the forces are such that I do not think Pete needs to worry about the posts moving once under tension. 

There is still a usability issue, though. Ganging them together somehow is definitely preferable from a user's standpoint. As with any bridge, ideally the luthier will set it up, then the player never has to think about it. 
Fixed pin bridges on flat top guitars are the ultimate in usability from the unsophisticated user's perspective. From a slightly more savvy user's perspective, a mandolin bridge or electric guitar bridge comes next, since there is a level of user-adjustability which comes in handy, yet no special tools are needed other than a screwdriver, allen keys, and a decent chromatic tuner.

----------


## Bertram Henze

> I've been trying to remember what this bridge system reminded me of. Eureka -- Koto.


That photo clearly shows that the discussion about full-contact vs two-footed bridges also applies for every single one of these.  :Grin:

----------


## sunburst

> IIRC, John Hamletts Tail pieces were near in-line with a standard bridge spacing.


Whew!!
I just found this thread, and before commenting, I thought it would be good if I read the whole thing. (That's an hour of my life that I'll never get back...)
Lots of misinformation from several sources, lots of erroneous speculation and assumptions... but I'm not getting into any of that, I'm just here to say that my tailpieces do not space the strings the same as the bridge. I thought about that when I was designing the tailpiece, and I concluded that, since the strings diverge from nut to bridge, in order for them to actually cross the bridge in straight lines, they would need to diverge from bridge to tailpiece by an amount that kept them all in straight lines from nut to tailpiece. Different string spacings at the nuts and/or bridges of individual mandolins would compromise that, so it isn't even possible to design a tailpiece that works for all mandolins and keeps the strings straight from nut to tailpiece.
Add to that, the fact that I see no good reason for having the strings run straight from nut to tailpiece, and add to that the fact that we're only talking one dimension here... (perhaps it would be better if they crossed the bridge straight with no break-over angle) and once again, I see no good reason for "straight line" tailpieces (with normal bridges). Add to that, the strangely wide look of a "straight line" mandolin tailpiece, and the aesthetics of the thing are starting to suffer, and for no good reason (IMO).
After going through all that in my mind, I opted for aesthetics instead. I measured the distance from the bridge to the tailpiece, transferred that distance toward the nut from the bridge (with fairly standard string spacing), and measured the total width of the strings at that point (near the end of the fingerboard). That was the total string spacing I used in my tailpiece design, so the strings converge at the same rate going each direction from the bridge. It is a subtle thing, but I think it improves the look of a mandolin, and is completely overlooked by many tailpiece makers.

So... that's a long way of saying that, no, my tailpiece would not work for what you are trying to do, Peter. In the case of your experiment/study, there actually _is_ a reason for the strings not being deflected to the side as they cross the bridge, so it looks like you will (as you have already concluded) have to make something to do the job.
As for the spreader you've settled for so far, as long as you are using it with all bridges you try, you've controlled that variable so it isn't a big problem scientifically speaking. With a wide tailpiece instead, however, I think you'll get results that are perhaps closer to "real life".

And for the record, I think I agree with the "respected scientist/luthier who is a member of these forums" "that phase interactions in bridges is not significant enough to warrant such an exercise", but don't let that deter you. Direct observation can be a great learning experience even when we think we already know the answer, even if we find out we _did_ already know the answer.

Oh, and one more thing... we've got 8 strings here, why only 4 bridges???  :Confused:

----------

David Houchens, 

Jim Adwell, 

Marty Jacobson, 

Pete Jenner

----------


## Jim Garber

It is late for me so I did not read every post here but got some idea. 

Just for historical background, DeMeglio mandolins often (if not always) had a string tensioner positioned after the bridge, evidently part of the Demeglio system which was patented somewhere around the turn of the last century. However this tensioner was actually screwed into the top and, sadly, there were not four separate bridges.

Here's what one looked like back in 1901. I don't know if that helps anything...

----------

Pete Jenner

----------


## Pete Jenner

> Oh, and one more thing... we've got 8 strings here, why only 4 bridges???


It's all I could afford.  :Smile:

----------


## Pete Jenner

Progress is slow due to other commitments but I've made a coupling plate which will mean I'll have to adjust height using washers until I devise a better system.





I'll do recordings with and without the coupling plate and with the old bridge.
The string spreader will remain but sans the supporting blocks.

More soon I hope.

----------


## Shelagh Moore

I'm using a very similar concept for a fretless solid stand-up bass design I'm working on where the individual post bases will bear down on a piezoelectric strip to add a different dimension to the coil pick that I'll also fit. I'll be interested to hear your comments when you're up and running Pete.

----------

Pete Jenner

----------


## Pete Jenner

I'd love to see it Richard.

----------


## David Houchens

Dang, I'm wrong again. I confess, I didn't measure both ends but it sure looked even to me. Sorry for any problems this may have caused. Hope nobody rushed out and ordered the wrong thing on my say-so.

----------


## fscotte

> Progress is slow due to other commitments but I've made a coupling plate which will mean I'll have to adjust height using washers until I devise a better system.
> 
> 
> 
> 
> 
> 
> 
> I'll do recordings with and without the coupling plate and with the old bridge.
> ...


Adding the coupler - doesn't this essentially make it into the very thing you're trying to redesign?

----------


## Pete Jenner

> Adding the coupler - doesn't this essentially make it into the very thing you're trying to redesign?


I'm not really trying to redesign anything. I'm just trying to find out more about bridges.
Having said that, if this design works, it allows a way of adjusting action and intonation on each pair independently. Additionally, we may discover more about the relevance or otherwise of such things as foot length.

This exercise is NOT an attack on the more traditional bridge designs but IS an attempt to understand them better. There is no pass or fail here.

----------

David Houchens, 

Paul Kotapish, 

Rob Zamites

----------


## Jim Garber

For some odd reason, I might think that this would evolve to a acoustic mandolin version of this  :Smile:  :

----------


## Timbofood

I think it's kind of a cool project, not that I wish to attack it. I appreciate the thought you are putting into this Peter. Might a piece of sheet brass ( pierced as you have the ebony)give the spacing support and be thin enough to allow the use of your adjustment screws?

----------


## Dave Cohen

Since there was a phantom mention of me in a post or two, I will add a post to this.  

Multiple strings on a single bridge or even multiple bridgelets are endemic enough to plucked strings that the subject has long since shown up in textbooks.  All here could have saved some time and also zeroed in on the correct physics of the matter by doing some reading.  The most pertinent introductory material is in the Fletcher & Rossing text, "The Physics of Musical Instruments, 2nd Ed."  The pertinent sections are section 4.9, "Vibrating String Coupled to a Soundboard", pp 119-120, and section 4.10, "Two Strings Coupled by a Bridge", pp 120-125.

There is a lot of conjecture in this thread (and in many others) about "what bridges do".  The catch is that except for tall, thin violin family bridges, they don't really do anything that the top plate itself doesn't do.  Even a violin bridge doesn't have any of it's own motions until up around 2.5 kHz and higher.  Plucked string instrument bridges don't just move in some fashion and impart that same motion to a top plate.  There is no "bow loading" or anything goofy like that.  Instead, they impart the force pulses from the strings to the top plate, and the top plate in turn moves in its' _own_ allowed set of motions (the 'normal modes' that I have so often mentioned).  So, to the extent that a top plate moves up and down ("trampoline mode", aka (0,0) or T(1,1) mode), the bridge moves up and down with it.  Similarly, when the top plate rocks sideways ((1,0) or T(2,1) mode), the bridge rocks sideways, and when the top plate rocks longitudinally, again, the bridge rocks longitudinally with it.  As with strings, the overall motion of a plate is the sum (actually a "Fourier superposition") of all of its' normal modes of motion.  Consequently the bridge, like the top, is undergoing a Fourier superposition of all of those same top plate motions.

So what does all of that have to do with Pete's bridge experiment?  Plenty.  What it tells us is that the separate bridge posts are not really very 'separate'.  His configuration may decouple the string pairs a bit from what they would be with a typical bridge saddle, but even so, the decoupling will not be complete, b/c the strings are still coupled through the top plate.  Imo, there won't be much decoupling at all, but I can't be sure of that without doing the experiments.  So, have at it, Pete.

----------

Pete Jenner

----------


## Pete Jenner

Thanks for that input Dave.
Have you got any recommendations about how I should do the measurements or indeed what to measure?

----------


## Killian King

> Heres a shaot of a Hamlett tail piece. Never seen masking tape used to dampen the strings between bridge and tailpiece. Dead on inline with bridge.


What a piece of work.

----------


## Eric Oliver

To encourage Mr. Pete in his search to reduce crosstalk or phase additions or subtractions...as if I know what that is...is there a way to have a mandolin top that would have separate top segments for each bridge string post?
I am thinking of the cracked Charlie Sawtelle Martin guitar top.

----------


## Bertram Henze

> ...is there a way to have a mandolin top that would have separate top segments for each bridge string post?


Since the neck would contribute a little coupling as well, it would be best to have 4 different mandolins with one bridge post each...  :Whistling:

----------

derbex, 

Jim Adwell

----------


## Dave Cohen

> To encourage Mr. Pete in his search to reduce crosstalk or phase additions or subtractions...as if I know what that is...is there a way to have a mandolin top that would have separate top segments for each bridge string post?
> I am thinking of the cracked Charlie Sawtelle Martin guitar top.


You can put all of the cracks or slits in the top you want.  It will not alter the main normal modes of the top.  If you look at holography (aka interferometry) data, you will see that the shapes of the normal modes go right through the soundhole areas as if they weren't there.  Holes or cracks are not a barrier to the modal motion of a plate.   To create a barrier that will impose a node (and hence a phase reversal across the nodal line), you need something massive, like f'rinstance a very large brace.  Even that won't change things much for the very lowest frequency modes.  So the direct answer to your question is that there is not a practical way to "separate" the strings.  It would just be contradictory to what top plates actually do, or for that matter, need to do.

----------


## Pete Jenner

An 40 fret mandolin with one pair of strings might work.

Dave, did you see my question?

----------


## Dave Cohen

> An 40 fret mandolin with one pair of strings might work.
> 
> Dave, did you see my question?


You mean w/ regard to ideas about measurement?  Yes, but I forgot to answer.  Sorry.  How you measure depends on what you want to measure, and what you want to measure depends on the question you want to answer.  If you look in the sections I referenced in the Fletcher & Rossing text, there are a couple of different things you might want to look at.  One is string frequencies.  Section 4.10 points out that a string coupled to another string through a bridge (saddle) will have it's pitch (aka frequency) thrown off very slightly by the interaction as the pitches of one string approaches that of the other.  The problem with just plucking the strings and doing an ft spectrum is that the combination of your sensor, computer, and software probably don't have sufficient resolution - mainly the computer and the software.   Those measurements don't work well enough for that experiment with ordinary 44.1 K resolution.  Maybe w/ 196 K resolution, if you have that.  The other thing to measure based on sections 4.9 and 4.10 is impedance.  You could also measure something like accelerant, as the two are related (see the Appendix to chapter 4).  You would do that at your various bridge saddle points.  May want to damp the strings for that, or maybe not.

----------

Pete Jenner

----------


## Timbofood

This is so cool! I am virtually a moron with respect to the physics but, the thought behind all this is fascinating!

----------


## Dale Ludewig

Dave, I've seen the interferometry and so forth, as you know.  I hope this is related to this thread.  What would happen if a crack or a narrow saw kerf were to run the entire length of the top, rim to rim lengthwise.  I know the plate doesn't seem to notice a hole in it, like ff-holes or an oval hole,  but the plate is still a 'whole', with a hole in it.  Assuming one could build a top that would support the string tension, do you think it would still act the same being coupled only at the rim?  I would think that at that point, it's no longer a plate, certainly not what it was before and the behavior would be drastically changed.?  Just thinking.

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## Dave Cohen

> Dave, I've seen the interferometry and so forth, as you know.  I hope this is related to this thread.  What would happen if a crack or a narrow saw kerf were to run the entire length of the top, rim to rim lengthwise.  I know the plate doesn't seem to notice a hole in it, like ff-holes or an oval hole,  but the plate is still a 'whole', with a hole in it.  Assuming one could build a top that would support the string tension, do you think it would still act the same being coupled only at the rim?  I would think that at that point, it's no longer a plate, certainly not what it was before and the behavior would be drastically changed.?  Just thinking.


In my post #106, "accelerant" should have been "accelerance".  Damn software thinks it is smarter than me.   Not that it's all that difficult to be smarter than me, except that the @#$ software is actually _dumber_ than me.

Your question is one I hadn't thought about before.  Can't say it is something I would want to try.  What you are describing is two independent half plates.  They wouldn't be completely independent, because they would be _coupled_ at the tail and the heel of the body.  Assuming you had independent half bridges to drive each half plate, you would have twin plate modes at a higher frequency, since modal frequencies depend on plate size, among other things.  Not a good thing.  Also, both half plates would be coupled to the same air mass in the body cavity, and also to the same back plate motion(s) through both the cavity air mass and the ribs.  It is an oddity that someone might well want to try (not me!), but it opens up some cans of worms.

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## Timbofood

I am in complete accord about spell checking software!

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## Jim Adwell

> Dave, I've seen the interferometry and so forth, as you know.  I hope this is related to this thread.  What would happen if a crack or a narrow saw kerf were to run the entire length of the top, rim to rim lengthwise.  I know the plate doesn't seem to notice a hole in it, like ff-holes or an oval hole,  but the plate is still a 'whole', with a hole in it.  Assuming one could build a top that would support the string tension, do you think it would still act the same being coupled only at the rim?  I would think that at that point, it's no longer a plate, certainly not what it was before and the behavior would be drastically changed.?  Just thinking.


What a bizarre idea.  I'm tempted...  But how could one brace the two tops without joining them somehow other than with the rim?


EDIT: a longitudinal brace on each side at the edges nearest the center might work.

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## sunburst

> What would happen if a crack or a narrow saw kerf were to run the entire length of the top, rim to rim lengthwise.


I saw such a mandolin once, many years ago. I don't think I knew who built it even then, and if I did I surely would have forgotten by now anyway (most likely). The top was made as two separate halves with about 1/4" gap between them. I didn't see any "accelerant" spectra or anything like that, but it sounded a lot like an oval hole mandolin, so whatever goes on in that top, my guess is that it is something like what goes on in an oval hole top.
It seems that anything we can think of, someone has already tried it...

One of my silly ideas is to do a similar thing but make the top 3 separate pieces with two slots about where the f-holes usually go. Maybe I'll get to that in my "spare time"... or maybe whomever has already tried it will chime in here soon and save me the trouble.

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Jim Adwell

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## Jim Garber

A lot of this is flying way over my head. I know this prob has nothing to do with anything we are talking here, however... take a look at this oddball Gelas mandolin:

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## Pete Jenner

> A lot of this is flying way over my head. I know this prob has nothing to do with anything we are talking here, however... take a look at this oddball Gelas mandolin:


I'd actually thought of making a bridge like that for my 12 string guitar to see if it reduced bellying.

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## Astro

As usual I can plead total ignorance on this thread. But even if this type design has no effect on tone, doesnt it at least make it easier for set ups ? Especially long term after notches get worn, sound boards settle, preferences change with different players, ect.

I have always wondered if it wouldn't be a design improvement to have the tuners and end pin hooks all lined up straight with the string spacing so that such a sharp lateral turn of the strings at both ends would be diminished. Would that effect tone, sustain, string life, tuning ease?

And btw Pete, where's the whammy bar ?

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## belbein

Mr. Jenner, I admire your creativity.  I have no opinion on whether the current bridge technology is "as good as it gets" or isn't.  I will just observe that the history of science teaches us that every time we say "it's as good as it gets" we find out that we left something out of our equations.  And throughout history, it's been the lonely old inventor, working in his pajamas and down-at-the-heels slipper, with a half-drunk bottle of dark ale on his workbench in his dank workshop in Kiwiland, who pushes technology forward.  

OK, well maybe not always in Kiwiland.

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## Pete Jenner

> Mr. Jenner, I admire your creativity.  I have no opinion on whether the current bridge technology is "as good as it gets" or isn't.  I will just observe that the history of science teaches us that every time we say "it's as good as it gets" we find out that we left something out of our equations.  And throughout history, it's been the lonely old inventor, working in his pajamas and down-at-the-heels slipper, with a half-drunk bottle of dark ale on his workbench in his dank workshop in Kiwiland, who pushes technology forward.  
> 
> OK, well maybe not always in Kiwiland.


Thanks Bob but I sleep in the nude and always finish my Dark Ale.  :Wink:  TMI?

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## Bertram Henze

Well Pete, that adds a few injury hazards to those already present in any workshop.  :Whistling:

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## Pete Jenner

What can I say Bertram? I like to live dangerously.  :Smile:

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## Timbofood

Peter, don't go there, PLEASE!

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## JeffD

Is this the kind of thing that one would use COMSOL Multiphysics software to model? I mean, is enough known that an accurate acoustic model could be developed, which would predict what effect radical design changes would have?

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## Bertram Henze

> Is this the kind of thing that one would use COMSOL Multiphysics software to model? I mean, is enough known that an accurate acoustic model could be developed, which would predict what effect radical design changes would have?


Any model must do two things:
- produce an audible result so we know "how it sounds",
- validate itself against a known design (e.g. an A5), so we can believe what we hear.

And the effort must be cheaper than just building wooden prototypes (some of which would have to be built anyway, in the end).
The big advantage of such a model would be that whatever the result, we would be perfectly able to explain it and thereby rule out any interesting speculation in endless Cafe threads (did I say "advantage"  :Confused: )...

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## Dave Cohen

Re models:  Models are "good" to the extent that they "work", and they "work" if they give the same result as experimentally observed behavior.

There are two types of models possible for string instruments.  Both have been done, and are occasionally revisited and refined.  One type is the simplistic model, employing a few masses as oscillators.  The other is the discretization of an actual instrument shape, employing powerful software such as FEM (aka "Finite Element Matrix") or BEM ("boundary Element Matrix) programs, very expensive.  There is some freeware FEM out there, but it is much more limited than the pricey stuff.

The simplistic models use a single mass for each vibrating part of an instrument.  The two- and three-mass models (Christenson & Vistisen, Caldersmith, etc.) were done in the late 1970s and early 1980s.  The two-mass model used one mass on a spring for the top plate, and a second mass for the mass of air, also on a spring, in the soundhole region.  The three-mass model used a mass for the top plate, another for the soundhole air mass, and a third for the back plate.  These experienced early but limited success.  The two-mass model predicted two peaks for the first or main body resonance, while the three-mass model predicted three peaks for the main body resonance.  What we actually see is two main peaks in some guitars (and mandolins), three in others.  Depends on whether the instrument has what Trevor Gore calls an "active back" (plate).  John Popp derived a simple four-mass model in 2010.  Wasn't peer reviewed, just presented at an ASA meeting.  Iirc, Trevor Gore also derived a four-mass model, but didn't see profound differences from the three-mass model.  Both of the four-mass models used a mass for the top plate, a second mass for the air in the soundhole region, a third for the back plate, and a fourth mass for the ribs.  Imo, the limitations for both Popp's and Gore's models were in experimental data.  _All_ of the simplistic models show limitations w/ regard to higher body resonances.

FEM or BEM models break a CAD representation of an instrument into a bunch of discrete rectangular elements - the more the merrier.  Each of the elements is governed by Newton's laws of motion.  Each element is also "coupled" to its' neighboring elements by simple spring relationships.    The overall behavior of the instrument is computed by "brute force" computational power.  The problem with those models is that they need some experimental parameters for input, which are best gained from actual experiments with actual instruments.  The alternative is to just try "best guess" values for those parameters, then keep iterating the values until the results converge to agreement w/ experiment.  So we are back to the limitations of experiment once again.  Some early discretized modeling of a classical guitar was done by Antoine Chaigne, and a few more attempts by others since then.  Much more of that stuff in the violin world than for plucked strings.

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Michael Lewis, 

Pete Jenner

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## Pete Jenner

I won't be doing any modelling. I've barely got the time to do the other measurements.

Dave, how do I measure impedance and accelerance?

Can you come here for a couple of weeks? :Whistling:

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## sunburst

> I won't be doing any modelling.


Me neither. I'm afraid the days of that possibility are long past for the both of us...

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Pete Jenner

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## Dave Cohen

> I won't be doing any modelling. I've barely got the time to do the other measurements.
> 
> Dave, how do I measure impedance and accelerance?
> 
> Can you come here for a couple of weeks?


Sure, I can pay a visit to Oz, if someone gives me a grant for the cost of the trip.

To measure accelerance, you need to measure the _motion_ of a plate.  The most direct and affordable way now is to purchase accelerometers on a chip, such as those used in hearing aid sensors.  In olden times, accelerance was sometimes measured using a phono cartridge as a sensor.  The fancy way is to use a _shaker_.  The shaker has a mechanical "head" placed in contact with the plate, which literally shakes the plate in response to the signal from a signal generator.  The shaker head also has an accelerometer built into it.  Accelerance, admittance, impedance, and other response functions are all related (see Fletcher & Rossing text, appendix to Chapter 4), so the signal from the sensor for one can be converted by your computer into another.

If you are really intent on making measurements, be prepared for the possibility that your experiment(s) will be inconclusive or worse.  That is part of doing experiments.  It is what points you in the direction of the next experiment(s) you will need to do.  Just one guess how I know that.

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## Timbofood

Some questions simply lead to more questions! Is that right Dave?

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