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| bridge locate theory http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=22378 |
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| Author: | mikemcnerney [ Fri May 15, 2009 5:54 am ] |
| Post subject: | bridge locate theory |
I'm pretty confused about where the bridge goes? If someone could push me in the right direction. I am building a 000 14th joined, 25.4. In the campiano book if I am getting it correctly he says to measure down the centre line to the centre of the saddle, in my case, 25.4. I have spoken to maker of many guitars who measures from the 12th fret down the high E string & adds 2mm through 1/3 the thickness of the saddle & makes his straight front bridge parrell with nut/frets. The saddle is slotted at the specified angle on my design? Mike McNerney |
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| Author: | Mark A Thorpe [ Fri May 15, 2009 6:37 am ] |
| Post subject: | Re: bridge locate theory |
The bridge is parallel to the frets and nut. Where I place my bridge is the scale length ends up 1/16" on the bridge, From the 1/16" on the bridge I compensate from there, more compensation on the low E and less on the high E. |
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| Author: | bluescreek [ Fri May 15, 2009 7:00 am ] |
| Post subject: | Re: bridge locate theory |
Setting a Bridge and explaining compensation and the variables of intonation: This is not that difficult and I am sure you will hear more than one theory. This is the method I have been using and one I learned from Dave Nichols of custom pearl. All I can say is that it works very well. You must first know your line of center from the neck. I use masking tape and mark the tape so in front of the bridge I know where that center line is. Do not assume the tops center is where the bridge is to go. Once you have center established you can begin the actual plotting of where it should be. You need to consider these variables . ( 1 what action height do you want to go with ) ( 2 string gauge ) (3 the strings physical properties ) This effects the placement in that higher action will pull strings sharp , and a heavier gauge seems to need a touch more compensation. I am figuring the placement using normal gauge ( lite and med ) and an action height that is around 4/64 to 7/64 Ok now you know the center , you need to set the bridge on that line and square it up . This is using a 3 degree compensation angle as does martin . I feel this will get you the best intonation that you can get on a fretted instrument. . I suggest a 1/8 saddle slot. The heavier slot allows for better single string compensation. Recap: center line and square Now follow the line of the first E and low E and center the lines to the bridge holes. I like to have a minimum of 1/16 from the edge of the fretboard. This is to check your bridge pin positions are matching your neck taper. So along the line of the 1st string ,if I have a 3/32 bridge I will want to position the bridge so the front of the saddle will fall at the position of scale length doubled ( nut to 12th fret 12.7 doubled = 25.4 plus 1/8 inch for compensation) The reason we do this , is that you are trying to match a dynamic length ( on that is in constant flux ) to a static ( actual fret placement ). So in essence a long scale ( 25.4 scale will place to 25.5 ) This extra length of compensation allows for the strings to stretch as you play them. If I am using a 1/8 saddle I will place the line more to the center of the saddle. I do this for the saddle compensating later. You have more to work with on the 1/8 so this allow tweaking in both directions ( flat and sharp). The human ear will notice a sharp note easier than a flat . I then measure along the line of the lower E and place that 1/8 inch longer than the hi E. So you are looking at the lines along where the string would be placed these measurements. Hi E 25.5 and low E 25.6 For short scale ( 24.9 you want ( Hi E 25.0) 9 Low E 25.1) again this is from the position of the nut to the front of the saddle on 3/32 saddles On 1/8 saddles you can place the bridge with with the line .25 inside the saddle. Now you have the bridge located. At this point I drill through the 1st and 6th string holes and pin the bridge so it won't move when I clamp it. Recap: Center - square - compenated. Hope this info helps john hall |
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| Author: | Fred Tellier [ Fri May 15, 2009 7:43 am ] |
| Post subject: | Re: bridge locate theory |
I like to have jigs for things and made a copy of the Stewmac Saddlematic and if you follow their instructions on using it the intonation comes out very close. I have used mine 4 times and needed only a little filing of the saddle to get the intonation correct. I use the Luthier Suppliers center finder to get a centerline and square up the bridge and then the Saddlematic to get the distance from the 12th fret. http://www.stewmac.com/shop/Tools/Special_tools_for:_Bridges/Saddlematic.html Fred |
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| Author: | Ken Franklin [ Fri May 15, 2009 9:07 am ] |
| Post subject: | Re: bridge locate theory |
I just set the high and low E strings. I use a straight edge from the nut to the saddle to make the distance from the fretboard edge to the string equal for both strings. (Maybe a little closer on the bass side for those who like to play with their thumb over.) Then I set the distances like John 25 1/2 for High E and 25 5/8 for low E on an 1/8 inch saddle. I use LMI's templates for slotting the fretboard. My saddles are slanted back 7 degrees to help with compensation at different action heights, but I start off at 3/32 at the 12th fret. |
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| Author: | Alan Carruth [ Fri May 15, 2009 1:23 pm ] |
| Post subject: | Re: bridge locate theory |
Theory: Guitars are set up for 'equal temperament': the cumulative error that you'd get from adding up twelve 'perfect' fifths is divided equally among all the intervals, so that everything except octaves is a little bit off, but nothing is so far out as to make it too unpleasant. The fret distances are usually calculated as if the string tension was not going to change as you use the guitar, and as if the bridge and the nut were mounted on a rigid base. But, of course, the string tension _does_ change when you fret the strings: when you push the string down it gets longer. Just how much longer will depend on the action height, and, to a lesser (but still important) degree, how much relief you use, and on other things. Just how much the tension changes will depend as well on the material and construction of the string. Generally speaking, the less stretchy the string material (the higher the Young's modulus) the greater the tension change for a given displacement. All else equal, a fat string will change tension more than a thin one. We're not so much interested in the tension change per se as the change in pitch it causes. It turns out that the change in tension for a given string will be the same for a given displacement in a given place, no matter how tight it is to begin with. Thus, a plain steel string .020" diameter might see a 1/2# increase in tension when you push it down on the 12th fret on your guitar (just to pull a number out of the air), and that change in tension will be the same whether it's tuned to high E (329.6 Hz) , or G (195.9 Hz). But the E string started out with about 63# of tension, while the same string tuned to G was only pulling 22.5#. That added half pound of tension from displacing the string makes a lot more difference in the pitch of the G than the E, and the pitch change will be the same for any plain steel string no matter what diameter. That's why plain Gs 'bend' more. One way we try to 'compensate' for the pitch change induced by string stretch is by moving the bridge a little further away from the nut than it 'ought' to be. This more or less works, since the strings are farther off the frets as you move down the fingerboard toward the bridge. On the one hand, the percentage of extra length gets greater and greater (the added length is the same, but the string itself is, in effect, shorter) as you go down, but you push the string down more, too. In theory you ought to be able to calculate this. In practice it's not so easy. For one thing, you'd need to specify everything very exactly, and that includes how hard the player pushes down on the strings. There are also a lot of 'non-linear' things going on, that throw the math off. And aside from all of that, there is the motion of the bridge and, to a much lesser extent, the neck, to take into account. In the end, most of us start out with some amojunt of compensation that seems to work well enough for the high E (which usually needs the least compensation), and set the saddle at an angle that makes all of the strings come out 'pretty close'. I don't think it's possible to get every note on every string to play 'in tune' perfectly. There are too many things going on that throw the pitch off. and besides, this is equal temperament: if you get it 'just right' it's still going to sound 'off' by it's very nature. We probably get closer than most pianos. though. |
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| Author: | bluescreek [ Sun May 17, 2009 7:58 pm ] |
| Post subject: | Re: bridge locate theory |
thanks for the information Al , May I print this out for reference? thanks |
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| Author: | Alan Carruth [ Sun May 17, 2009 8:04 pm ] |
| Post subject: | Re: bridge locate theory |
Print away! |
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| Author: | martinedwards [ Mon May 18, 2009 8:03 am ] |
| Post subject: | Re: bridge locate theory |
I'm a much more "hands on" rather than theory kind of guy. I make my bridge, bung in a temporary saddle, and the I use a home made tail peice to anchor the two E strings. then I use the same technique as setting the position of an archtop or mando bridge to get it 95 % right. then I remove the varnish underneath and glue it down. |
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| Author: | TonyKarol [ Mon May 18, 2009 9:33 am ] |
| Post subject: | Re: bridge locate theory |
On about 100 guitars and counting .... take half the scale length, measure from the 12th fret as I comp the nut as well, add 2.5mm, and place the saddle slot at this point, in the middle of the slot, between the D and G string position. I use a 3mm slot differential over a 70mm slot. IIRC, only on one guitar could I not get the G string FORWARD enough to get the octave in tune (remember - on the typical acoustic these days, the G string is the thinnest - core, not windings count here, and requires very little comp, or very similar to the high E) - I may have been a touch off though, it was an early one. |
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| Author: | Alain Desforges [ Mon May 18, 2009 9:45 am ] |
| Post subject: | Re: bridge locate theory |
Tony, if I recall correctly, we had this conversation in Erie, or maybe somewhere else, where you comp the nut 1mm. Correct? |
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| Author: | TonyKarol [ Mon May 18, 2009 1:10 pm ] |
| Post subject: | Re: bridge locate theory |
Yep .... |
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| Author: | Greg [ Mon May 18, 2009 6:57 pm ] |
| Post subject: | Re: bridge locate theory |
I have found a simple jig to locate the bridge. It corrects intonation and and centerline and srting spacing all at once. Using te 12th fret not on high and low E-strings and compare against the 12 fret harmonic. Use a tuner but you can do it by ear. Move the whole bridge toward the guitar tail if the harmonic is sharp and towqrm the neck if flat. I use a laser line to mark the midline but I also "eyball" the course of the strings along the fretboard. |
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| Author: | peterm [ Mon May 18, 2009 7:07 pm ] |
| Post subject: | Re: bridge locate theory |
Greg, that's a very cool idea! Thanks for sharing! |
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| Author: | Parser [ Mon May 18, 2009 8:36 pm ] |
| Post subject: | Re: bridge locate theory |
I ran the numbers on this stuff awhile ago. To make a long story short, the slight bit of extra length that is added to most of the strings really doesn't make as much difference in the note being played as the extra tension that is added when you fret a string - especially if your action is higher than it should be. The way that most people line their bridges up puts the high E string just a skosh past the theoretical scale length. The larger strings then increase slightly in length as you go across the fingerboard. The reason for this is that larger diameter strings behave less like the ideal theoretical vibrating string in that they have significant bending stiffness at the point that they break over the bridge. This effectively shortens their vibrating length. If anyone is interested, I'd be happy to email a copy of the spreadsheet I made up. Trev |
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| Author: | Parser [ Tue May 19, 2009 9:09 pm ] |
| Post subject: | Re: bridge locate theory |
If you guys are interested, I have posted a copy of this spreadsheet to my website: http://www.peakeguitars.com/Vibrating_String_Calcs.xls The inputs are all in the highlighted cells. The equations are for plain strings only...! Overwound strings require a few differences in terms of the calcs. Thanks, Trev |
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| Author: | Andy Zimmerman [ Tue May 19, 2009 9:25 pm ] |
| Post subject: | Re: bridge locate theory |
Tony You use 2.5mm which is close to what I do. Would you do the same for a nylon string??? |
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| Author: | Alan Carruth [ Wed May 20, 2009 1:29 pm ] |
| Post subject: | Re: bridge locate theory |
Parser wrote: "The larger strings then increase slightly in length as you go across the fingerboard. The reason for this is that larger diameter strings behave less like the ideal theoretical vibrating string in that they have significant bending stiffness at the point that they break over the bridge. This effectively shortens their vibrating length." If that's the case, then you'd need significantly more compensation if you increased the break angle over the saddle, since the string would be bending more. Do you see this? |
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| Author: | Parser [ Wed May 20, 2009 7:37 pm ] |
| Post subject: | Re: bridge locate theory |
I think the resistance in bending and in conforming to the "ideal string" is primarily a function of the tension of the string, the material, and the diameter. The breake angle might affect it some, but I wouldn't expect it to be significant. If it was significant, I would expect that the string would not lay straight across the bridge (it would "hump up" immediately after breaking over the saddle). The reason I ran this analysis is because I was pretty stymied at the time as to how you could bump the saddle position back some nominal amount while at the same time you would "fret" (haha) endlessly over the spacing between the frets, etc. This analysis shows that the distance to the saddle appears to play a much smaller role to the action in terms of intonation. It affects it, but not by near as much as a low action. Trev |
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