# Instruments and Equipment > Builders and Repair >  Bridge Compensation

## Jim Baker

Can anyone tell me if there is a formula for bridge compensation based on scale length and string gauge? Making a bridge is next on my list for my octave mandolin. Thanks

----------


## Jim Baker

Could I assume that, in order to measure compensation for each string one would need to make a temporary bridge, string up and check intonation on each string?

----------


## Schlegel

Not only gauge and length but material affects the compensation too. I suspect it may be too complex with all the various string types for a simple formula.  I've never made an octave bridge, but I have hand compensated mandolin and mandola bridges.  Small adjustment, tune up and check.  Lather, rinse, repeat.  It's such a small area to file that it's really the repeated removal and tuning up that takes the time.  You can file with a bridge still on the top, but it's very easy to make one bad slip.  :Frown:

----------


## Willie Poole

I posted on here one time a few months ago, "why the compensated bridge " back in the early days bridges were straight across with no compensation...I made a saddle years ago with no compensation and installed it on one mandolin and it seemed to have the correct intonation, I sold the mandolin with that bridge on it too....I have had a few antique mandolins and all of them had non-compensated bridges so It`s beyond me why they have them...I asked it it had anything to do with the gauges of modern strings and some of the builders on here said gauge size didn`t matter, it was the length and the fret spacing that made it needed to be compensated....Good luck in getting an answer....Willie

----------


## Soundfarmer Pete

I would suggest that gauge size (or more correctly tension) does matter (based on my guitar experiences)!
Suppose you have a guitar that intonates perfectly at the 12th fret in standard tuning. Drop the low E to a D and check the intonation - it will be wonky. Since I play mostly DADGAD, I make up my string sets from singles with heavier gauges for the dropped notes.
With the wound strings, I wouldn`t be surprised if different manufacturers use slightly different wire for the core so even if a string is say .040", it probably won`t have the same tension from manufacturer to manufacturer

----------


## David Newton

String compensation is so complicated, I think the best way is just to trust those little bridge tops with the back-and-forth saddle positions.
Just joking, but I don't know a better way to state it. I have also had success with a straight line saddle, slanted.

----------


## Graham McDonald

There is not a simple formula, though Mike Doolin wrote a comprehensive article for American Lutherie a few years back on calculating compensation. An OM like your will need around 2mm compensation on the top e string and 3-4mm more than that on the bottom G. It gets a little more complicated depending on whether you want to use a plain or wound a string. A plain a string will need another 2-3mm compensation behind the e string, but a wound a, because of the thin core wire will want a shorter string length than the e. Compensation is much dependant on  the diameter of the plain steel wire, whether as as the core of a wound string or a plain steel string.

For a pin bridge octave I usually start by positioning the front of the saddle slot around 1mm past the theorectical scale length and start from there. For a floating bridge it will be a matter of little bits of wire to mark the saddle setbacks. 

Here is a diagram of a four course saddle if that is any help

cheers

graham

----------

Rob Zamites

----------


## Paul Hostetter

No fixed formula, because there are so many variables. That said, Gibson established a pretty good standard, if you have a typical 13-7/8" scale and J-74 strings. 

There are also many, many earlier threads on this issue - search the archives.

----------


## Jim Baker

Good place to start. Thanks guys.

----------


## Paul Hostetter

> Here is a diagram of a four course saddle if that is any help


This is precisely the opposite of the orientation Gibson originally intended. In this image is a '20's F-5, w/original bridge. This is how the bridge was meant to be oriented.





I find that the D, A and E work well but the G still tends to play sharp up the neck, so I often do a different setback for that:

----------


## Graham McDonald

Maybe it is just my diagram, but it looks pretty close to the Gibson saddle as far as I can see. It is what I have been using for Octave mandos/ bouzoukis for a very long time. Jim B is building an octave not a standard mando, and the stringing is a little different.

cheers

graham

----------


## Jim Baker

I'll be starting off with a set of J80's. I think they are 12, 22w, 34w, 46w. Just a starting point.

----------


## Graham McDonald

For the J80 set the .022w will be the forwardmost (if that is a word) contact point, the .012 and .034 1-2mm behind behind, and the .046 back another couple of mm. As Paul points out, getting the G to play in tune can be tricky.

cheers

graham

----------


## Jim Baker

Graham, can you tell me is that because the core of the A course strings will be smaller than the E course strings? Just trying to understand a bit. 
I have a 17 fret tenor banjo that I was having A string trouble with. When I switched to a wound A string it solved the problem. 

Thanks

----------


## Graham McDonald

The core of the .022w string will be something like a .008, and so needs less compensation than the .012p e or the .034w D, which will have a core around .010 or .012. There will hopefully be someone here who can explain the science behind it, but my understanding is that it is the core diameter (or plain string diameter) which has a major part in how much compensation is needed, rather than the overall diameter of the string.

cheers

graham

----------


## Paul Hostetter

Wound strings intonate very differently than plain ones. Using a typical Gibson mandolin bridgeright-side up or upside-downwith its compensation for _two_ pairs each of plain and wound strings on an octave mandolin, which has only one course of plain strings and three pairs of wound strings, strikes me as a recipe for hopelessly intractable intonation. I replace such bridges all the time. Depending on the scale, action and so on, I use either of the two fairly similar patterns below for octave mandolins:

----------


## Michael Lewis

Mandolin scale is much shorter than OM and is much more sensitive to intonation issues.  The shorter the scale the more critical the fret placement and compensation.  As explained, there are so many possible variations that there is no rule or established pattern to follow so one needs to adjust the compensation for each course of strings while on the instrument.  The saddles Steve Smith supplies with his Cumberland Acoustic bridges have a nice wide area on the top so there is room to make the needed adjustments.  Once you set the intonation you can remove the excess material on the back edge of the saddle.

----------


## thistle3585

I just strung up a 20.75" scale OM that I made and I used a mandolin bridge as a starting point to set the intonation and it ended up being spot on.  I don't think I could get it any better and I did use a .022 wound A string.  I am still working on the best for the G string.  By the way, along these same lines of setting up a bridge, what type of spacing do you use on your longer scale instruments?  My fretboard looks way too large from the 12th fret up because the spacing on the mandolin bridge is too narrow.  Should I consider increasing the string spacing or narrowing the fret board on the next one?

By the way, I used on of Steve Smith's bridges that he uses on his Redline Travelers.

----------


## Ben Milne

> 


Interesting stuff... where is the mando-matic bridge from, Paul?

EDIT - found your answer Here... 

So I gather If you had one of your hypothetical mando-matic bridges, you'd basically use it to intonate each instrument, and then duplicate the compensation in a fresh cut...

----------


## thistle3585

Vanner98,
That is a reality.  Here is what I came up with for my electric mandolins.  I've made them in brass and wood, but the wood ones are easier to make since I run them on the CNC.  I don't see why you couldn't make a base for them to determine compensation.  The only downside is their height.  The saddle piece itself is 1/2" tall although I have sanded up to an 1/8" off them.  I can't recall what the hole spacing is , so I don't know if they will fit on a standard mandolin base. 

Note:  The saddles are tilted because I don't have the correct ones in there.  
Andrew

----------


## Graham McDonald

My octave/bouzouki fretboards are 34mm wide at the nut and 44m at the 12th fret. The spacing between the outermost strings at the bridge is about 44mm, but adjusted as required to have the strings almost parallel to the outside of the fingerboard. The line of the outside strings almost follows the flair of the fingerboard, which uses the same proportional flair as a guitar fingerboard. The top e is 2-2.5mm from the edge and the bottom G about 3mm from the edge at the nut. This does mean that a standard mandolin bridge (with an outside string spacing of around 40mm) can be a bit tight, but I don't use mandolin bridges on OMs/bouzoukis anyway.

It seems as though setting compensation at the bridge can be a variable thing, and does suggest that different instruments do need different setups. Ah, the joys of lutherie  :Smile: 

cheers

graham

----------


## Jim Baker

Thankyou guys. I'll post a picture when I get it working.

----------


## Paul Hostetter

> So I gather If you had one of your hypothetical mando-matic bridges, you'd basically use it to intonate each instrument, and then duplicate the compensation in a fresh cut...


Exactly. But in its absence, any bridge will work: you position the bridge so that the intonation is precisely where you want it for each course, one at a time, starting with the E, and then you measure from nut to point of contact. Or if you want to start with a block for a saddle, get the E properly set from the forward edge, and adjust the other courses from there. Kind of hard on the strings taking it off and on, but you at least know you have it. Or, as Michael suggests, get one of the Cumberlands and start there and tweak away.

----------


## oldwave maker

21.5" scale length gdae, daddario phosphorbronze.048-.034-.023-.013 YMMV

----------


## Jim Baker

I have a new question about bridge compensation. I have converted my first octave mandolin to a bouzouki with a 25" scale. I am octave stringing the G and D courses. 

I now have to make a new bridge.

Here is my question: In the G and D course is there a different compensation between the wound string and the plain string?

----------


## Paul Hostetter

There sure is, but most people don't bother doing separate compensations within the pair, but focus on the lower of the two. I've done it the more complicated way for some folks who really appreciated the effort.

----------


## Rob Grant

FWIW: I've just completed an octave mandolin with a strap hanger. The scale is ~23 inches (580mm in the "real world"<g>). I basically used the same bridge compensation that Graham shows in his publication "The Bouzouki Book" (2004). As far as my string guages, bridge height, etc goes, Graham's diagram is pretty spot on (thanks Graham). I'm using wrapped bronze strings on the G,D and A and a plain wire on the E. The Guages are 44-32-20-11.

Here's a photo of the bridge and the mando...

----------


## Jim Baker

Thanks guys. Paul, I guess it's best to read the intonation and work it up from there. With the longer scale is doesn't sound bad just using the octave mandolin bridge but it's not perfect.

----------


## Paul Hostetter

If you settle on a set of gauges you know you're going to continue to use, it might be worth dialing in the details for the unwound octaves on the two bottom courses.

----------


## Jim Baker

I bought a set from elderly that are labelled bouzouki medium. .011", .011", .016", .016", .028"w, .011", .040", .016".  They sound pretty good although the A course seems a tad weak. 
One thing I did was put the wound strings on the bass side of the G and D courses. It seems to work o.k. but is not normal.
When I get a bridge that works I'll post a picture.

----------


## Bernie Daniel

For the mandocello all strings are wound so the compensation is monotonically progressive -- longest scale, C-course to shortest scale, A-course.  See image of a Gibson K-1 bridge.  So would this relationship hold for any mandocello, regardless of scale length, if all strings were wound?

----------


## Jim Baker

I'm finding that, even using the O.M. bridge on the bouzouki unchanged, the intonation is very close. The longer scale is much more forgiving I'd say. I expect a mandocello scale would be even more so.

----------


## multidon

As a general rule a wound string needs to be shorter than an equivalent solid string to intonate correctly. I used to have a Guild Starfire guitar with factory Bigsby. It came with a matching Bigsby bridge, which had a solid aluminum base with a rocking one piece solid aluminum saddle. The saddle was compensated for a set with a wound G. Now, most guitar string sets come with a solid G, so this severely limited my string choices. Typical guitar compensation has the wound E, A, and D getting gradually shorter, then the solid G gets longer, with the remaining solid B and E getting gradually shorter again. With this particular bridge, and anything else set up for a wound G, wound E, A, D, AND G all get progressively shorter, then the plain B gets longer and plain E shorter than the B. The only set I could find for that guitar that would intonate correctly was a D'Addario set that included a wound G. Don't you just love D'Addario? If you can think of it, they have a set of strings for it.

Paul is definitely on the right track with his OM bridges. I have a bit of trouble with my mandola. Most mandolas has 3 wound courses and one solid, whereas mandolins have 2 wound and 2 solid. So if a maker uses a bridge with mandolin compensation on a mandola it will, in my opinion, be impossible to intonate, at least on the D course. Tilting my bridge a bit helps but a custom cut mandola bridge would be ideal. The Good thing for me that I rarely play above the 5th fret!  :Smile:  The mando-matic is an intriguing idea. A bridge like that should work as well on a solid electric mandolin as it does on an electric guitar. But you NEVER see anyone try anything like that on an acoustic, particularly flat-tops. One might wonder if something with that much metal in it would transmit vibrations to the top effectively.

----------


## Bernie Daniel

Here are some additional examples of bridge compensation -- the first is an image of my Weber Absaroka bridge (~21" scale).  The saddle is not compensated but instead this is achieved by the base of the bridge being canted toward the treble side (longer scale on the bass strings).

The other two images are of a 1940 Jumbo arch top guitar with what I think is typically called a Jazz bridge. 

Notice that in addition to the continuous compensation across the saddle  the bridge is also designed with a "bias" toward the bass strings.  I assume this is done to bring out the volume of the bass strings and might be something to try for octaves and mandocellos?

----------


## Phil Goodson

> Here are some additional examples of bridge compensation -- the first is an image of my Weber Absaroka bridge (~21" scale).  *The saddle is not compensated* but instead this is achieved by the base of the bridge being canted toward the treble side (longer scale on the bass strings)........


Looks compensated to me.

----------


## Bernie Daniel

> Looks compensated to me.


You are right there is some -- actually but most of the compensation is achieved by actually setting the bridge base on a line not orthogonal to the neck.

What do you know about the base of the guitar bridge?   Why is it canted to the base side of the guitar?  Would this be something that could be productively applied to a mandocello bridge?

----------


## Ben Milne

> orthogonal


Twice in a week...

----------


## Bernie Daniel

> Twice in a week...


I assumed everyone who studied quantum mechanics would surely know what orthogonal was...but see figure below if you don't.  Line AB is orthogonal to line CD -- on the Weber octave the bridge base is NOT orthogonal to the neck.  

OK, there you have it.  I just get tired of writing "perpendicular" sometimes don't you?  

Now do you happen to know the answer the question I raised about the arch top bridge?  :Smile:

----------


## Dave Cohen

Uhh, Bernie, surely you know that orthogonality in the Hilbert space formulation of Quantum mechanics is quite the superset of what you were implying in your last post.

http://www.Cohenmando.com

----------


## Ben Milne

I'm all for using a wider range of descriptions than just perpendicular Bernie.  
The word was mentioned a few days ago in a grain direction thread and it was highlighted that someone had to look it up as rarely had the term been used in discussion here before.

Using your diagram as a reference, and the line of AB as string direction, are you talking about having bridge contact point C closer to the tailpiece and bridge contact point D nearer the cutaway? 

It seems this would be a way to dial in intonation in small increments without having to get the chisel out.  On the bridge in your photo this actually brings the curved feet back around to similar positions on the sound board.  If the angle were too aggressive it may begin affect the interaction with the tone bar beneath the top.

Dr Cohen has obviously spent some time in development to end up with his bridge design and may have more insights as to how tone would be affected if the feet were straight and canted like you say.

----------


## Bernie Daniel

> Uhh, Bernie, surely you know that orthogonality in the Hilbert space formulation of Quantum mechanics is quite the superset of what you were implying in your last post. http://www.Cohenmando.com


Hmm well I see you really did study quantum mechanics.  Thank God for mathematicians!  No, I could not  have affirmed  that I still knew that.  I looked into the matter enough to get through my physical organic chemistry course in g. school (had Jack Hine, RIP for it  by the way).  But upon reflection, I think I would rather have the location of my mandolin bridge defined in inches rather than eignvalues.  :Smile: 

But on that arch top guitar bridge (2nd and 3rd images) do you know what Vega was trying to accomplish by shifting the base of the bridge over toward the bass side of the top plate relative to the saddle?  Was this to get more energy into the bass side tone bar?

----------


## Bernie Daniel

> I'm all for using a wider range of descriptions than just perpendicular Bernie.  
> The word was mentioned a few days ago in a grain direction thread and it was highlighted that someone had to look it up as rarely had the term been used in discussion here before.
> 
> Using your diagram as a reference, and the line of AB as string direction, are you talking about having bridge contact point C closer to the tailpiece and bridge contact point D nearer the cutaway? 
> 
> It seems this would be a way to dial in intonation in small increments without having to get the chisel out.  On the bridge in your photo this actually brings the curved feet back around to similar positions on the sound board.  If the angle were too aggressive it may begin affect the interaction with the tone bar beneath the top.
> 
> Dr Cohen has obviously spent some time in development to end up with his bridge design and may have more insights as to how tone would be affected if the feet were straight and canted like you say.


I was just being silly with the wordsmiting!  :Smile: 

But yes I think you have the idea on the octave.  I think Bruce Weber just kind of figured out a clever way to put some compensation angle into the base of the bridge without making it too obvious.  If you lay a straight edge along to top of that saddle you can see right away that that a center line through the bridge base would lie at a pretty good angle relative to a line through the neck.  

But my main question is with that guitar bridge -- why is the base shifted to the bass side relative to the saddle?

----------


## Ben Milne

Oh, the abbreviated treble side foot. 
Now I can see what your enquiring mind is pondering...

----------


## Phil Goodson

> ....
> But my main question is with that guitar bridge -- why is the base shifted to the bass side relative to the saddle?


The base isn't really SHIFTED, it's shortened on the treble side.   I don't know the answer you're looking for, but I recall that Red Henry did some experimenting with the length of the base feet and found increased volume when the feet were not overly long.   Whether this translates into using the shorter foot to fine tune the treble tone or volume, I have no idea.  Surely it has nothing to do with intonation though.
 Would be interesting to query the builder, but unless it is a factory built instrument, I speculate that the builder from 1940 might not be able to answer. :Frown:

----------


## Bernie Daniel

> The base isn't really SHIFTED, it's shortened on the treble side.   I don't know the answer you're looking for, but I recall that Red Henry did some experimenting with the length of the base feet and found increased volume when the feet were not overly long.   Whether this translates into using the shorter foot to fine tune the treble tone or volume, I have no idea.  Surely it has nothing to do with intonation though.
>  Would be interesting to query the builder, but unless it is a factory built instrument, I speculate that the builder from 1940 might not be able to answer.


I agree -- shortened on the treble side better describes the situation.  It is a factory instrument -- Vega (Boston, MA) -- and I have found that it was one of their "standard" bridges.  So they must have thought it has some redeeming features?   

One thing that interests me is the compensation on that bridge is not much different than that on my Gibson K-1 mandocello.  Now both the guitar and mandocello have similar scale lengths but the last two strings on the guitar are plain whereas all on the mandocello are wound of course.

I am strongly tempted just to use that bridge when I convert the guitar to a mandocello but I am thinking maybe I should go with a conventional (symmetrical) base so as to spread down-vectored force over a larger area.

----------


## Paul Hostetter

> The other two images are of a 1940 Jumbo arch top guitar with what I think is typically called a Jazz bridge...Notice that in addition to the continuous compensation across the saddle the bridge is also designed with a "bias" toward the bass strings.  I assume this is done to bring out the volume of the bass strings and might be something to try for octaves and mandocellos?


I assume you mean this one:



This is compensation in the simplest sense, with no real adjustment for the B. The overall angle pretty much mimics what Gibson and Selmer both used. It had nothing to do with bringing out volume (how could it?) but strictly a way to get the strings to intonate properly up the neck. Except, of course, for the B. 

BTW, back in the day, B strings were typically wound, not plain, which mean that the separate setback for the B wasn't really necessary.

If you regard the bridge, as I do, as a brace, this shortened bridge looks like trouble. I'm just finishing a restoration on an old Gibson A mandolin that had a too-short bridge and it really did some damage to the toptoo much pressure in too small an area.

----------


## Joseph Fisher

Great post ... my mandolin has a compensated bridge and it makes all the difference in intonation.

----------


## Joseph Fisher

What company 1st introduced the compensated bridges?

----------


## Steevarino

Since CA bridges have been mentioned a time or two here, I'll offer another potential solution.  I could provide you with a bridge saddle "blank" or two.  You could then carve or file whatever compensation scheme you wanted in it.  I know one trick that guitar makers and set-up folks sometimes do is cut very small lengths of guitar string (very short, maybe 1/2" long) and place them between the uncut saddle and each string course.  Once the strings are under tension, you can move these tiny sandwiched string-bits (one for each set of strings) forward and backward, keeping a sharp eye on your strobe as you go along.  Once you get all four of the little string-bits where you want them, you can take a sharp pencil and mark both sides of their location.  In theory, this should give you the compensation locations you are looking for.  File or carve to the lines, slot it, and see if this was a good idea or not!

----------

CedarSlayer, 

CJFizzix

----------


## CedarSlayer

I love it Steve! 

You could also put masking tape down on either side, and use a straight bridge to test intonation on all the strings.  After making sure the bridge is at a right angle to the strings check all the strings intonation.  Each time you find the right position for a string, mark the tape on both sides.  Then you have a chart of the correct offset for the instrument and and strings you are using.

Bob

----------


## Stephen Perry

Steveevarino has a great idea.  When I'm faced with an odd intonation problems, I simply make a new bridge saddle or whatever the strings go over, string it up, and start playing and cutting back. All the measuring in the world doesn't seem to take into account all the variables that exist. Just gradually cutting back the contact point until each string or pair or whatever we have intonates reasonably well seems the way to go about it. I've done this simultaneously at the nut and at the saddle on a few instruments. If you are a perfectly stable, sane, rational, and methodical person, that type of double ended approach will soon cure your problems. You will rapidly become just as neurotic, homicidal, and suicidal as the rest of us.

A quick web search on compensating at the nut will turn up wonderful articles. This is well worth considering.

One of the problems with working on fretless instruments all the time, and on listening very closely while I do my acoustic work, is that I have become very pitch tuned. These fretted instruments are always badly intonated. And don't get me started on the impossibility of my piano.

----------


## onassis

Stephen, I'm glad you brought up the subject of intonation adjustment at the nut. I hear of it in the guitar world, but I can't say I've ever seen it on a mandolin. Been on my mind lately because I've noticed a bit of wonkiness in my intonation, and thought the easiest fix might be at the nut. Just a bit of fine work with the Dremel. Of course, you could do the same at the saddle, just seems like much less material to work with.

----------


## Fretbear

Never had to try it on a mandolin (cutting back the nut point contact) but it was the only cure recently for the high E on a new Recording King R0S-06 guitar. The saddle point had given all it had in it's position, so I gave it a little more on the nut, and voila, it would then play in tune without a capo. I fit some some paper shims under the string before I went after the nut just to be sure.

----------


## mrmando

Just did a little setup work on a 1925 snakehead. Came here to double-check compensation. The bridge has been on backward for goodness knows how long ... the saddle's even slotted the wrong way. It's already playing better.

----------


## Paul Hostetter

Gibson employee Ted McHugh invented and patented both the adjustable truss rod and the height-adjustable bridge in 1921. Gibson had a compensated one-piece bridges for guitar and mandolin well before that, of course.

----------

