"Reverse" intonation, miss a bit of info on intonation / frets position

Discussion in 'Hardware, Setup & Repair [BG]' started by ELynx, May 16, 2018.

  1. Story:
    I side-shimmed neck on my bass to get correct neck angle and better string alignment. Afterwards I adjusted the setup, especially focusing on intonation since tension and string length changed. During that I used "cable" tuner, not my everyday clip-on because a) it feels more accurate b) clip-on does not really feel vibrations when string is not opened.

    What I did:
    Started practice today, wanted to check if bass is in tune and if some changes to intonation are needed. Was too lazy with to get "cable" tuner, went for clip-on. Then, to get vibrations to the "head" side of string I plucked left of 12th fret, and got far-off readings. Then I realised that to get same (?) string length I need to fret on 12th fret from side of 13th fret. This got me readings pretty close to BEADG octave up, but actual BEADG. I checked, intonation in regular way is set, same tuner gives BEADG in usual way.
    I realize that saddles don't adjust string length from nut to 12th fret, so what I was getting in reverse is not adjusted; but how it then works as a whole? To make saddle adjustment even frest should move with it? Imagine fret positions painted on piece of rubber, and that piece of rubber is stretched - not only length is changed, all frets move a bit.

    How bass may be "in tune" if I intonate only for open string and 12th fret, what magic makes other frets produce correct pitch? I suspect that both length and tesion are involved. Or I was lying to myself every time I did setup, and it is very improbable to get all notes correct.
  2. mbasile

    mbasile Mediocre Bassist of a Year Supporting Member

    Mar 16, 2015
    Austin, Texas
    The magic is the properly placed other frets. It’s is less magic, and more math.
    funkinbottom and sissy kathy like this.
  3. sissy kathy

    sissy kathy Back to Bass-ics Gold Supporting Member

    Apr 21, 2014
    Arbutus, MD
    When you intone an instrument, you are stretching the string to match the spacing of the frets. Think of that rubber band as the string. You are making the rubber band marks line up with the frets. As the rubber band stretches the marks get closer to the frets. When the 12th mark lines up, so do all the others.
    Angel Rabbit likes this.
  4. Lofreck


    Apr 25, 2013
    If you stretch the string, the increase of its tension will push the frequency up much faster than increase of the length would pull the frequency down. So tension wins. The distance from 12th fret to the bridge should be slightly bigger than distance from 12th fret to the nut in order to compensate bigger tension when string is fretted. The higher the action the bigger should be the difference. The "harder" the string, the bigger should be the difference.
    Angel Rabbit and ELynx like this.
  5. sissy kathy

    sissy kathy Back to Bass-ics Gold Supporting Member

    Apr 21, 2014
    Arbutus, MD
    Right and that is why you never get a perfectly tuned instrument, the string stretches as you fret. And the different gauges have different lengths. The frets are really only a very good approximation of tuned. Either go fretless or pay several thousand USD more for a bass with those squiggly frets, but be aware those squiggly frets will only work for one gauge of one brand of string. Straight frets are a compromise. Also realize that while you may be in tune with your squiggly frets, the guitars with straight frets won't be, but you are the one that will sound out of tune. Don't let the theory muddy your thoughts; accept that fretted instruments are imperfect.
    Last edited: May 16, 2018
  6. OK, understood. I missed idea how both factors work together, especially that tension changes pitch faster.

    I will pass on squiggly frets :), I can barely discern pitches to pick a tune. Plus frets will get naturally squiggly some day, although not in the good way.

    Thank you for answers, this cleared another thing for me in setup.
  7. lz4005


    Oct 22, 2013
    Wait, wait, wait.
    Shimming a neck does not change string length or tension unless you did it very very wrong.
    A shim normally changes the neck angle, which doesn't alter length or tension. A shim on the side of the pocket will keep the neck from shifting to the neck left/right but not change anything else.

    And intonation doesn't have anything to do with changing the scale length. It is a compensation for thicker strings being less flexible. Frets are positioned with the idea of a mathematically perfect string, which assumes a high degree of flexibility. Intonation adjustment compensates for reality differing from theory.
    ddnidd1 likes this.
  8. Yes, a shim on the side of pocket. But before I installed it neck was rotated clockwise, not misplaced. So when I adjusted it treble side strings got a little bit more tension, and bass side strings got little less tension.

    For second part - I have to process that. I thought that saddle movement changes total string length, and those millimeters count for pitch. Then tuning in with tuners changes tension, which changes pitch too.
    So with tuner I set string tension, and string sound to (say) A4. Then I move saddle so middle of string (zero point for standing wave wave 2 times shorter / 2 times higher pitch A5) is right over the 12th fret, thinking flageolette. But that changes open pitch, so I go back to step and tuner. Rinse and repeat until sufficient level of approximation is achieved.
  9. lz4005


    Oct 22, 2013
    By rotated do you mean the neck was twisted? A shim is not an appropriate fix for a twisted neck.

    And regardless, shims don't alter string length, which is the only thing that makes string tension increase if you're using the same strings and the same tuning.

    There's a difference between scale length and string length. Scale length is the distance from the nut to the 12th fret multiplied by two. You then adjust the saddles to compensate for real world strings not being mathematically perfect.

    You're misunderstanding the intonation procedure. Tune the open note, check how far off the octave harmonic is from the fretted note at the 12th, then slack the string (if you're increasing length, so that you don't strip the screw), move the bridge saddle, retune the open note and re-check the harmonic vs the fretted note. Repeat as needed.
    ELynx likes this.
  10. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    I wonder about those "squiggly" frets. Bit of a problem if you do any string bends. Probably not recommended for blues.

  11. sissy kathy

    sissy kathy Back to Bass-ics Gold Supporting Member

    Apr 21, 2014
    Arbutus, MD
    I got the impression the strings were too close to one side of the fretboard and he shifted the neck sideways and then shimmed it to hold it there. Theoretically, shifting the neck would change the string length, and tension. Retuning cures the tension difference.
    Last edited: May 18, 2018
    ELynx likes this.
  12. lz4005


    Oct 22, 2013
    I've seen video of Steve Vai playing a guitar with squiggle frets. His rhythm guitarist and bass player were using non-squiggles. Bends sounded the same. Everyone sounded in tune with each other.

    This is another option for micro-managing intonation.

    Using a fretless bass solves all intonation issues. And creates lots of new ones.

    Maybe it's a language issue. "Rotation" doesn't imply left/right alignment to me. But maybe that's what he meant.
    ELynx likes this.
  13. Yes, this too. Let me make a great mechanical picture of quality, in world-renowed CAD software.
    On the left, I explain what I mean by rotated. Not twisted (happy for me). Beside strings not really sitting with edge of fingerboard strings were not 100% between pickup poles. I pulled neck straignt so strings sit on fretboard, and align with pickups. Then I checked where in neck pocket I have a gap. Gap appeared between right side of pocket and neck. I shimmed that gap, without even taking off the neck, with a piece of plastic cut to size of pocket (will use wooden weneer when I will do the trip to "arts and crafts" shop). Place I shimmed is red on the right side of image.
  14. These squiggles? I thought some special height...
    I do think they solve something, for sure. But I will pass, because learning to play this thing is like learning riding a bike with "squiggly" frame. Sure, turning left may be much easier, but luck with riding anything else.
    (I am not against any variations on bass, pros can and will use such things and do a good job with it. I is just so above my level of usefulness that it is useless to me).

    For some reason I get to post in late evening, and my English degrate significantly; mixing of native and English terms in my head does not do this process easier either. Thanks for patience so far to everyone.
  15. Angel Rabbit

    Angel Rabbit

    Mar 26, 2019
    Hi, Good morning from the Caribbean, Kathy, the way you explained here made my whole picture a lot clearer,awesome . Thanks to all for the great input,great day.
  16. ixlramp


    Jan 25, 2005
    Wut ... don't play the string on the wrong side of a fret to get vibrations to the headstock, the results will be completely wrong and completely irrelevant, don't let this confuse you. Clip-on tuners are only for tuning open strings.
    Use a cable tuner to intonate.
  17. ixlramp


    Jan 25, 2005
    The (unfortunately and exasperatingly) commonly recommended method of checking the pitch of the 2nd harmonic against the pitch of the 12th fret note is a slightly sloppy method that is prone to errors.
    However yes, this method very roughly results in all frets in tune.

    The accurate and error-proof way to set intonation is to use a tuner and check the tuning of every note along a string, because 'that's what intonation is'.

    The widespread misunderstanding and the important point is this:

    'Checking the 2nd harmonic against the 12th fret note' is a method only for when you don't have a tuner.
    Because: Playing a harmonic is the only way to create a higher pitch exactly in tune with the open note, against which you check the intonation of a higher fret.
    If you have a tuner this method is ridiculous because you are choosing to not use the tuner. You would obviously better off using the tuner to check the pitch of the open note and the pitch of the 12th fret note, or far better: Check the pitches of the open note, fret 1 and every 2nd or 3rd fret up to the highest played fret.

    I suspect that because guitarists learn the 'no tuner' method very early in their musical life, many therefore never think about it, question it or realise how ridiculous it is when you do have a tuner.
    I suspect it became common advice because most 'sources of guitar advice' chose to explain the 'no tuner' method in order to give advice that is also suitable for those without tuners.
    Last edited: May 3, 2019
  18. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    That won't work. Intonation is a compromise in two realms. First is that on a fretted instrument, the location of the frets is an approximation that does its best to handle variation in string gauges and the force applied to the string to fret it. The second is that in a twelve tone scale compromises have to be made for any given interval to be "in tune" in various keys. It's complicated, but was addressed as early as the 1700's by musicians such as j. S. Bach. Some modern day electronic tuners allow the user to select between various tempered tunings ("tempered" meaning modified from the accurate mathematical model), but there are several temperments (also called "sweetened tunings") available.

    So the first question when using a tuner is what do you tune to? The open string? The 12th fret harmonic? Theoretically they are the same thing an octave apart. But if you have a truly accurate tuner you may find that the two do not agree. And that variation can be due to the string manufacture. Even some high quality strings can exhibit a frequency shift between the open string and the octave harmonic. And even with a perfect string the way it is installed can cause a similar discrepancy. These differences are usually quite small, but they are there.

    Chasing perfect intonation is fruitless. What purpose does it serve? Will your audience be able to sense that the bass is two cents flat in the mix with a loud drummer, a guitarist who is equally inaccurate and a keyboard that is tempered entirely differently?
    Kro likes this.
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