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Thread: Bridge Compensation

  1. #26
    Café habitué Paul Hostetter's Avatar
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    Default Re: Bridge Compensation

    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.
    .
    ph

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  2. #27
    Registered User Rob Grant's Avatar
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    Default Re: Bridge Compensation

    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...

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    Rob Grant
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  3. #28
    Registered User Jim Baker's Avatar
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    Default Re: Bridge Compensation

    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.
    Jim Baker

  4. #29
    Café habitué Paul Hostetter's Avatar
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    Default Re: Bridge Compensation

    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.
    .
    ph

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  5. #30
    Registered User Jim Baker's Avatar
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    Default Re: Bridge Compensation

    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.
    Jim Baker

  6. #31
    Certified! Bernie Daniel's Avatar
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    Default Re: Bridge Compensation

    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?
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    Bernie
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  7. #32
    Registered User Jim Baker's Avatar
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    Default Re: Bridge Compensation

    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.
    Jim Baker

  8. #33
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    Default Re: Bridge Compensation

    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! 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.
    Don

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  9. #34
    Certified! Bernie Daniel's Avatar
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    Default Re: Bridge Compensation

    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?
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    Bernie
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  10. #35
    formerly Philphool Phil Goodson's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Bernie Daniel View Post
    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.
    Phil

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  11. #36
    Certified! Bernie Daniel's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Philphool View Post
    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?
    Bernie
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  12. #37
    In The Van Ben Milne's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Bernie Daniel View Post
    orthogonal
    Twice in a week...
    Hereby & forthwith, any instrument with an odd number of strings shall be considered broken. With regard to mix levels, usually the best approach is treating the mandolin the same as a cowbell.

  13. #38
    Certified! Bernie Daniel's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Ben Milne View Post
    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?
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    Last edited by Bernie Daniel; Nov-13-2011 at 8:11pm.
    Bernie
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  14. #39
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    Default Re: Bridge Compensation

    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

  15. #40
    In The Van Ben Milne's Avatar
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    Default Re: Bridge Compensation

    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.
    Hereby & forthwith, any instrument with an odd number of strings shall be considered broken. With regard to mix levels, usually the best approach is treating the mandolin the same as a cowbell.

  16. #41
    Certified! Bernie Daniel's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Dave Cohen View Post
    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.

    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?
    Last edited by Bernie Daniel; Nov-14-2011 at 8:44am.
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  17. #42
    Certified! Bernie Daniel's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Ben Milne View Post
    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!

    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?
    Bernie
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  18. #43
    In The Van Ben Milne's Avatar
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    Default Re: Bridge Compensation

    Oh, the abbreviated treble side foot.
    Now I can see what your enquiring mind is pondering...
    Hereby & forthwith, any instrument with an odd number of strings shall be considered broken. With regard to mix levels, usually the best approach is treating the mandolin the same as a cowbell.

  19. #44
    formerly Philphool Phil Goodson's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Bernie Daniel View Post
    ....
    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.
    Phil

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  20. #45
    Certified! Bernie Daniel's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Philphool View Post
    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.
    Bernie
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  21. #46
    Café habitué Paul Hostetter's Avatar
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    Default Re: Bridge Compensation

    Quote Originally Posted by Bernie Daniel View Post
    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.
    .
    ph

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  22. #47
    Bacon 1921'
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    Default Re: Bridge Compensation

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

  23. #48
    Bacon 1921'
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    Default Re: Bridge Compensation

    What company 1st introduced the compensated bridges?

  24. #49

    Default Re: Bridge Compensation

    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!

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  26. #50

    Default Re: Bridge Compensation

    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

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