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Do I picture this correctly, that the bridge/saddle assembly would thus be leaning towards the nut?
Originally Posted by northernbreed
That would feel very weird for anyone familiar with bowed string instruments. On those, the bridge is wedge-shaped and the rear side is meant to be perpendicular to the top meaning it seems to lean backward. I'm not exactly certain why this is - maybe the wedge shape is just to allow the top edge to be thin enough and the base (feet) be thick enough to support the combined tension of the strings. What I do know is that we learn quite early on to monitor the bridge for leaning forward because that's what they'll all do because of tuning and the pushing down on strings with the bow.
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10-31-2024 01:08 PM
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This is one of those cases where a couple of pics would tell the story a lot more clearly! But no, the bridge wouldn't be angled towards the nut. Rather, I often seen the bridge to be close to perpendicular to the plane of the strings coming from the nut to the bridge. Which doesn't seem ideal, but I don't know for sure. The Benedetto drawings show the first case I talked about where the bridge sits on and is is perpendicular to the top of the guitar's arch, and the strings bend over it at similar (but different) angles. Originally Posted by RJVB
One of my questions is if deviations from this kind of symmetry (the strings bending more or less evenly over the saddle, as opposed to the strings coming in pretty level to the saddle and then angling over and behind to the tailpiece) would be less than ideal.
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On an archtop, the strings angle down from the saddle to the nut, meaning the break angle is <90° (= perpendicular). You could make that angle 90° by moving the bridge/base towards the tailpiece. For me that gives a forward leaning bridge/saddle.
You'd be right on a flattop with a regular flattop bridge. And there it's very clear that you don't want any forward lean; the difference in break angle on both sides of the saddle (and in string height) creates a torque that would flip the saddle if it weren't held, and any lean into that direction will increase the strain on the bridge slot (or so I would think).
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The wisdom on this topic in the guitar community is surprisingly low. The fact that you are raising the question indicates that you are on to something. Originally Posted by northernbreed
Anyone familiar with bowed string instruments, knows that there are different traditions and philosophies when it comes to the design of the bridge and its angle (tilt). Originally Posted by RJVB
Let's leave it there and remember that a guitar is a very different instrument.
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When it comes to the tilt of the bridge (tilted forward towards the nut, or backwards towards the tailpiece) there cannot be any universal truth, because there are a number of conflicting targets that cannot all be met at the same time. Which is not to say it doesn't matter. Actually, this could potentially be the difference between a good guitar and one that doesn't perform.
Here are a few parameters in play (there are more, but let's avoid the rabbit hole, shall we):
- Bridge post stability and stiffness (bridge posts strong enough to support a bridge that's not perpendicular to the top)
- String break angle (the steeper the angle, the higher the string force and pressure onto the bridge)
- Bridge height (the higher the bridge, the steeper the string break angle)
- Tailpiece height (if the tailpiece is height adjustable, string break angle can be compensated)
- String gauge and tuning (Heavy gauge means heavy bridge pressure. Open tunings alter the pressure.)
- Bridge radius (the effective radius depends on the tilt angle)
- Saddle slots (string contact and witness points depends on the tilt angle)
- Intonation (depends on most factors above, but in particular; a ToM; bridge having adjustable saddles is designed under the assumption that the saddle travels parallel with the string. When it doesn't there are consequences.)
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Shall we also forget that the archtop guitar was designed with the violin or cello in mind. Or more to the point, that the relevant difference lies in how the bridge transmits vibrations to the top but not in the physics that of the forces working on the bridge and its point of contact with the top? Originally Posted by JCat
But if my post was worded sufficiently clear and you really read it you'd understood that my message was that there are forces at play that will tend to pull the bridge/saddle forward and that this becomes worse the more the assembly leans forward.
I'm not a physicist so I won't claim there is an obvious solution or answer here, but dismissing several hundred years of "traditions and philosophies" (aka experience resulting in a single design principle) seems downright stupid.
Pity we can't ask Lloyd Loar but I'm guessing there must be a patent somewhere, and drawings showing how he thought about the question. (Wonder also if he knew the guitar and viola da gamba families are very closely related.)
That seems to be about as realistic as string companies specifying tensions at pitch assuming that there is no stretch. In this case I don't see how that design assumption can hold unless there are no break angles ... I can see how in practise it might be acceptable to have 2 near identical break angles but that would mean tilting the saddle in the direction of the steepest of the 2, so towards the tailpiece.bridge having adjustable saddles is designed under the assumption that the saddle travels parallel with the string. When it doesn't there are consequences.)[/LIST]
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OK, let's open this can of worms then, Originally Posted by RJVB
The adjustable ToM string saddles are supposed to adjust the length of each string to compensate for additional string tension when fretting. (The higher the string height, the higher the fretting tension, making notes pitch sharp unless compensated).
If a ToM bridge is tilted in any direction vis-à-vis the string plane, the saddles are travelling on a slope. Then it won't be possible to adjust string length without at the same time altering string height, which makes it very difficult (sometimes impossible) to intonate the guitar. Furthermore bridge radius is going to change with saddle travel. It's simply a mess and a moving target.
Fortunately a one-piece wooden bridge doesn't have this problem, still all the other parameters (and some more) in the list above are applicable.
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Hmmm, a can of worms indeed.
Screw-worms, even
OK, so what you were referring to is the plane of the sounding part of the strings (and how you mean "string action" rather than "string height"). Yes, I can see how you'd want to the micro saddles to travel along an axis that's parallel to the sounding length of the strings. In that case you'd probably want the saddles to be perpendical to those axes to prevent unnecessary shearing torques. Originally Posted by JCat
I still think you'd want the rest of the assembly perpendicular to the top though.
That isn't really true, is it?! The same principles still hold for each nut slot/string contact point, the only difference is that you can't adjust the position of those contact points w.r.t. each other reversibly. I suppose that an experience luthier who micro-compensates a saddle for a specific guitar will take care of setting the proper string length and string action. Any meaningful changes to string action as a result of adjusting compensation by rotating the bridge (changing the azimuth?) can presumably be minimised by increasing the saddle height on the side that was moved backwards?Fortunately a one-piece wooden bridge doesn't have this problem
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Yes the same principles apply to the string slots/contact points of a one-piece wooden bridge, also the fact that the effective radius depends on the tilt angle. And yes, an experienced luthier would slot the bridge to meet the desired radius and secure the witness points. However, when the top is arched, the effective bridge tilt and the effective radius depends on the exact location of the bridge foot. But this exact spot also depends on your string height/"action" preference, i.e the higher the bridge, the further back it needs to go and consequently it'll tend to lean backwards due to the arch of the top. Fortunately most archtops got an area somewhat flat where the bridge is located, thus having sufficient tolerance for various user preferences, provided of course your setup is not out of bounds. But some guitars got a really steep arch and then it's very obvious that bridge tilt depends on the location of the bridge posts (assuming these are perpendicular to the top). Originally Posted by RJVB
Now, consider this: If the bridge posts are located on an arch and square to the apex, when you adjust the thumbscrews to dial in bridge height, you are also going to change the lengths of the strings. This is less of a problem if the bridge is tilted backwards (as string length will increase with string height, like we want, but if the guitar got fixed bridge posts and the bridge is leaning forward, any increase in bridge height (using the thumbwheels) would cause string length to be shortened, i.e the opposite of what we want.
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So, back to my initial question ... and this is all relative to wood bridge/saddle combinations.
Here's the image (found all over the web) that shows how Benedetto apparently sees things for where the bridge assembly is ideally located relative to the arched top, the incoming slope of the strings from the nut, the slope of the strings from the saddle to the tailpiece, and ultimately, that the bridge is aligned vertically. Obviously the scale length, setup (string height, relief, gauge), and nut slot depths need to be accounted for where the bridge is located. And on this diagram, there is a fairly broad, flat area on the arched top for positioning the bridge fore/aft to take the above into account. Also note the steeper string slope after the bridge, but still a fair bit of slope before it.
Question is, what happens when the luthier starts to deviate from this - where the bridge is no longer perpendicular to the flat part of the arched top.
If it's leaning towards the nut, would most everyone say that's not optimal? Is it OK to lean it bit towards the nut, but past a certain point (say, when the bridge alignment starts to get close to being perpendicular to the string plane) then it's really not good? And yet, I see some fine archtops out there that start to get close to this.
And what about the bridge slanted/leaning a bit towards the tail piece? What happens then?
I'm guessing there's a range in there that is optimal for tone, intonation, evenness of forces applied to the saddle posts, etc..
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Guess I'm not yet completely braindead after all Originally Posted by JCat
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If you just look at the break angles you'd probably be tempted to think that the idea bridge orientation would be such that these 2 angles are as identical as possible. Possibly even a bit tilted backwards if you consider the differences in weight between the 2 sets of string segments.
(But could it be that the saddle-stringholder distance is dimensioned such that the break angle difference compensates for the weight difference?).
I think that we're probably overthinking this though. Bridge position is dictated by scale length, neckjoin fret number, but also by the kind of voice the builder is after. OTOH, the use of a domed top is very much a structural (aka architectural) consideration; these can be made thinner and yet withstand the pressure from strings.
Suppose an architect were to design, say, a church in a place with an almost permanent wind blowing out of the same direction, would he design the spire to lean into that those winds and thus slant the supporting dome and walls accordingly?
I guess what I'm trying to say is that in archtops the area where the bridge is supposed to go will probably typically be "flat" seen from the side and parallel to the top rim.
If you'd want to raise the bridge height you'd have to do what was done (sorry, again ^^) in the violin family, somewhere at the beginning of the 19th century. Re-neck to put the fretboard at a steeper angle (rake?).
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Read my posts again. What matters is you and your guitar. What "most everyone say" on most guitar related topics is based on what most everyone believe, aka folklore. Originally Posted by northernbreed
You have to figure out why your bridge is leaning and if there are consequences.
Are you able to tell if the tilt is on purpose by design, or if it's an unwanted consequence of poor design? Maybe your setup is out of whack, maybe something is broken?
About thumbwheels:
These are thin discs with a threaded hole in the center. Those threads are supposed to carry the load of the strings tuned to pitch. There's tolerance and there's wear and those thumbwheels tend to lean on the posts they are screwed onto. An old rock n' roll trick is to use two thumbwheels on each post, thereby stabilizing the wheels so that they won't tilt.
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What's the load again they'd be carrying in a typical setup, and how does that compare to what similar bolts 'n nuts might be carrying in, erm, real-world Originally Posted by JCat
applications? I've wondered about this myself (the posts in my stock Loar bridge were thinner than in the AllParts replacement) but despite the fact that my posts were indeed leaning a bit the thumbwheels always turned smoothly.
So yes, lean in the saddle can also be the result of the posts not having been installed too carefully, or they might have gotten bent somehow.
In the end it turned out that a good part of the perceived lean in my saddle was an optical illusion. The walls of both ends that go around the posts are in fact slanted giving the impression that the entire saddle was leaning backwards when looking from it sideways. I only noticed this when I got the assembly off, put the posts in straight and the saddle back on in its lowest position.
EDIT: something that's been at the back of my mind: if the saddle and posts are leaning w.r.t. the top surface where the bridge sits, isn't there a risk that the base will move while playing? I've had that happen in my resonator (biscuit+cone assembly shifting in the well), only in this case because the tailpiece wasn't properly centred on my instrument (so the shift was lateral).
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The drawing posted is not accurate, it's an idealized drawing. The top of most archtops is not a perfect arch from edge to edge, there are areas that are flat, and the bridge area is usually one of those, with little or no arching for some small distance. The bridge is also not in the center of the body longitudinally, it's much closer to the tailpiece end than shown in the sample drawing. That drawing can't be taken literally, it's just for illustrative purposes to show what the author wanted to emphasize.
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FWIW, these are the drawings I meant to refer to: https://benedettoguitarsarchives.com...archtop-plans/
As you can see, there is a flat area on top of the arch (maybe 2" or more) that would accommodate the bridge placement. Otherwise these seem pretty literal.
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The string pressure depends on the string break angle. If the string break angle would be 0 degrees the corresponding force would be null and the bridge foot would not stay put. When the break angle increases, the force increases up to some critical point when the integrity of the bridge assembly gets compromised; bridge tilts, posts bend, bridge radius gets flat and heaven falls down. Originally Posted by RJVB
This critical point, depends on the individual guitar, its individual bridge system, the user specific string set, tuning and last but not least, the user, i.e You.
A user that prefers high action and heavy gauge is dancing on the edge of the danger zone. Not all guitars and not all bridges are able to handle such extreme force:
If the guitar got a steep neck angle, then if the user prefers a dead straight neck (zero relief) the bridge must be jacked up very high to prevent fret buzz. This is going to put additional force on the bridge as string break angle gets steeper.
Try this; release the truss rod and see how the string height increases. Now you can lower the bridge. The string break angle is reduced and thereby the force also gets reduced.
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The bridge should be perpendicular to the top where it's mounted, IMO. If the bridge leans, it's usually because either the studs are leaning because the holes are too big or drilled crooked, or because the base was sanded more on one side than the other, and perhaps the base is not flat. Sometimes it's both, or all of the above.
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THAT is what I was looking for. Thanks! Originally Posted by sgosnell
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