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  • close to topic- fret spacing

    At long last I've gotten back to one old project, the alumitar- aluminum electic guitar. I found the figures I had calculated for fret spacing and wanted to check them for accuracy. Then I started reading about stretch compensation which counteracts the increase in tension of a string when you bend it to touch a fret. I was surprised at the relatively large difference in fret spacing when the compensation factor was put into the equation. For example, at the tenth fret, there's about a .070 difference in the position where the fret should be. That sure seems like a lot when you consider that the fret positions are calculated to four decimal places- not that I know of anyone who can saw a fret slot that closely. My questions, how close is good enough, say for a trained ear, and are there any frets which should be very finely positioned because an error there would be most noticable? I can imagine that at a harmonic, that fret position would be more critical.

    I've decided to go with the compensated figures since from one simple test using a keyboard and beat tones, the positions given seem to be right on the money. What I have read about equal temperment, etc, suggests that many of the notes could be altered slightly in their frequency (by positioning the frets differently than the standard formula suggests) to achieve a more pleasing sound. After all, hearing a guitar being played is supposed to be pleasant- not getting into the relative merits of differing types of music-.

    I'm aware of pretty much all the parameters regarding intonation and adjustments, including the effects of different brands of strings, the height of the strings, the curve of the fretboard under the strings, etc, but the rather broad range of possible fret positions seems like an anomaly to me. If a guitar is properly in tune, what kinds of changes in fret position might make it sound even better that it normally might? Does anybody ever add a compensation factor for average finger pressure?- that alone seems to me to be a much larger factor than small deviations in fret position.

    Comments, anyone?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    My questions, how close is good enough, say for a trained ear, and are there any frets which should be very finely positioned because an error there would be most noticable? I can imagine that at a harmonic, that fret position would be more critical.
    I haven't tested my frequency resolution in a long time but I do have perfect relative pitch. What that means is that if you give me a note I can then give back any other note accurately relative to the tone supplied. When I tested that back in high school I was good to about 1/4 cycle per second at 440 hz (American Standard A). Since the next semitone, B flat, is the 12th root of two higher at 466.16372 hz that corresponds to a sensitivity of about 1 percent.

    I don't know how my tone discrimination compares with others but it doesn't take much off key for me to notice. This is particularly apparent in the beat frequencies. In fact, I don't really like the equally tempered scale as it is not a perfect tuning.
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    • #3
      darryl, you might consider sending a private message to Frank Ford on this as I believe it would be right up his alley. Incidently, I'm may need to pick your brain as I'm pondering a lap steel project for the winter and since I'm a total newbie, I'm going to need some serious guidance.
      John B

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      • #4
        Never heard of it done at the frets. At the bridge, yes.

        The tuning of a guitar and even a piano are a comprimise. The human ear actually likes a tiny bit of what seems to be out of tune.

        Is this going to be an "all" aluminum guitar? Seems like it would feel cold. And prone to bad vibrations.
        Last edited by topct; 08-26-2007, 08:39 AM.
        Gene

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        • #5
          The human ear actually likes a tiny bit of what seems to be out of tune.
          Speak for yourself. I like perfect tuning. It does mean playing in only one key though unless you retune, a somewhat awkward proposition for a piano.
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          • #6
            Actually, there are a lot of aluminum guitars around. I suppose they are used to play light metal music...
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              Originally posted by topct
              The tuning of a guitar and even a piano are a comprimise. The human ear actually likes a tiny bit of what seems to be out of tune.
              In the visual art world it's called "evidence of hand". If it exist there, no reason it shouldn't exist in music. It's one of the reasons I maintain we live in a analog universe and not digital.

              As for the OPers question, I'm betting it ain't that critical. If it is, explain to me how they made guitars hundreds of years ago.
              Last edited by Your Old Dog; 08-26-2007, 09:33 AM.
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              • #8
                Originally posted by topct
                The tuning of a guitar and even a piano are a comprimise. The human ear actually likes a tiny bit of what seems to be out of tune.
                Temper is actually a little more complex than that. It stems from the oddity that if you set perfect intervals going up the scale, then perfect intervals coming down, you wind up with a slightly different note from where you started. Tempering is an attempt to deal with this remainder. If the error is distributed among all the intervening notes it's equal tempering. However, this seems to just make any key sound bad. The more common strategy is even tempering which distributes the error unevenly, assigning more of the error to keys that are used less frequently. That's why transposing a piece of music to a different key can make it sound different. If all things were equal, transposing a piece would make it just the same except at a higher or lower pitch. Because of the uneven distribution in even tempering the color of a piece can change in a different key. In modern times we've become accustomed enough to even temper that we hardly notice, but in the Baroque era they were much more sensitive and struggled with how to solve the problem. There some instruments made with multiple keys for the "same" note tuned for diffent keys so you could actually play the correct note in that key. Didn't turn out to be a very viable solution.
                .
                "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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                • #9
                  Darryl, did you happen to see this?

                  http://www.charliehunter.com/gear/novax.html
                  Gene

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                  • #10
                    Yep, I've played with people that say they have perfect pitch and they are constantly tuning the instrument because it never sounds right to them. When they get it right in one tune and we play another tune they start tuning again to get the strings right. We no longer stop playing for them to tune.

                    Having perfect pitch is a curse if you want to enjoy the music. They even complain that the music is out of tune on a recording, which I am sure it is to their ears.

                    I just tune it and play it and enjoy it. I'm glad I'm not afflicted with perfect pitch.

                    Most guitar finger boards have the fret slots cut with a CNC machine. They can program the spacing for the length of the strings from the nut to the bridge and have it sound ok but it will never be perfect and always sound off to those with perfect pitch.

                    I would suggest you buy a ready made finger board rather than cutting your own.
                    Last edited by Carld; 08-26-2007, 06:34 PM.
                    It's only ink and paper

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                    • #11
                      Topct:

                      My first reaction to that fanned fretting was positive, but then common sense set in. I can see how, let's call it second degree adjustments, like the odd angled fret, could be useful in compensating for differences in fretting lengths required for different string thicknesses etc, but how can it possibly be necessary for different strings to have different lengths ?

                      If a string is too long, open (unfretted), you just tune it - you tighten it or loosen it. Maybe to cope with some fret positioning errors, like the fretting compensation this thread is about, you might wish (theoretically) to have frets that aren't straight across, but lengthening the string isn't going to do anything.

                      Darryl:

                      Sorry about the OT. Have you inquired what the fretboards/fingerboards from the luthier suppliers are set to ? I've had this kind of thing on my project list for a while, but unlike the gifted few, I would have to have more recourse to calculation than to the ear to feel I had got it right.
                      Richard - SW London, UK, EU.

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                      • #12
                        Ok, well, first of all, the guitar in not all aluminum. There's some laminate in there, brass screws, and considerable stainless. There will be some maple laid in alongside the aluminum neck, and also some maple around the body. None of that is structural, so my thinking is that its main contribution is esthetic and mass. The nut on this guitar is an abomination of brass rollers and stainless pins. The strings are captive within this part so they can't get out of the groove, so to speak. This is important as will be shown later.

                        The bridge is a fairly understandable piece with individual height and length adjustments. Behind the bridge is the piece which constrains the ends of the strings, also in such a way that they can't leave the 'groove'. This piece has a sort of hinge action, and can be adjusted to tune all the strings at once, or taken off completely and easily. Again this is important.

                        The neck is held to the body using one knob, no tools required. This guitar comes apart in two major pieces, and can go back together again quickly and be in tune. Individual string adjustments put direct tension on the strings, so there's no unwinding going on when the guitar is apart. There are no tuning pegs to wind the strings onto.

                        The fretboard mounting area is flat, which is a compromise. I would have preferred to have a slight curve across the top of the strings, but this is how it will be. It's not a big deal to me.

                        The fretboard itself- this is going to be a build-up of sections with frets held captive between sections. As of this point tiday, I have about a third of these sections machined to individual sizes, and done according to the stretch compensated program to determine fret spacing. I'm exactly at the point where I need to make sure the fifth fret is exactly where I want it, and basically this is what prompted my questions.

                        Because finger action changes the tone produced more than about any other parameter, I wanted to include a corrective factor for this. If I find that a typical finger pressure against a fret results in the exact tone desired, then I will have suceeded in placing that fret correctly, regardless if the program says it should be somewhere else. As I suggested earlier, there is a considerable variation in fret positions when only one corrective factor is considered- and I want to include at least three factors, one ot those being 'does the note sound right'. The one compromise anyone must make is because every individual fret must work for all strings, so the result is that few notes will be exactly what they should be. For the sake of actual buildability, the equal tempered scale is used, and as suggested, it's not quite right- close, but not exact.

                        It's been interesting for me to educate myself on all this, and relate it to actual experience, that is, of having listened to the guitar being played, and pondering the 'imperfections', even though the guitar could be in 'perfect tune'. I've had decades to consider this, but only recently have I explored ways to improve on this situation.

                        Interesting read on the Charlie Hunter site. That's the first radical change in fretting and scale length I've seen to address some of the problems. It would appear that some practice would be needed in order to play one of those guitars. Maybe it's actually easier- hmm.

                        Anyway, it's back to the project now. Thanks for all your inputs.

                        John and Richard- I'm sure that by the end of this project I'll have some more insights into making it tick, and I'll share that for whatever it's worth. Others are certainly more knowledgeable than me on this topic, but maybe I can add something.

                        Last point- I guess that since this guitar is constructed of aluminum parts with substantial thickness, I can't really lay claim to having invented a new type of music, but light metal sounds like a welcome change from heavy metal. Had I gone thinner, I could have invented sheet metal music
                        Last edited by darryl; 08-26-2007, 08:10 PM.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                        • #13
                          I could have invented sheet metal music

                          No, I think that the "chink-a-chink" music of those that were sent way south by the English were a few years earlier.
                          Today I will gladly share my experience and advice, for there no sweeter words than "I told you so."

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                          • #14
                            Having perfect pitch is a curse if you want to enjoy the music. They even complain that the music is out of tune on a recording, which I am sure it is to their ears.
                            It can be a curse. I don't listen to music at all any more. That is one of the reasons.
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                            • #15
                              I build an accoustic guitar from fiber glass years ago. That's all fiberglass, no wood. Don't ask me; I was proving something. Anyway I built my fret saw machine strictly to 12th root of two fret spacing and once the bridge was set to produce true octaves the rest of the frets produced almost perfect tempered pitching.

                              No fiddle factors no nothing. Adjustable bridges used by electric guitar players and jazz musicians are seldom tweaked from string change to string change. From this I conclude that special compensation factors are more mystic refinement than anything else.

                              I suggest a test. Make a crude sample neck and stretch a string above some cobbled up frets. Tension the string with a precision scale on it. Fret the string and note the tension change. If the tension change is down in the third decimal place it's too subtle a change for listeners to note.

                              I still have the fret sawing machine. Anyone interested?

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