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There's one bit of guitar theory that I can't really get my head around and it has to do with saddle position. Conventional wisdom as I've learned it is that the distance from the nut to the middle of the saddle should be = scale length + about .125".

How can this make sense? The nut line and fret positions are all "perfect"...and then we just tack on this extra bit at the end? We certainly wouldn't want to tack on an extra 1/8" from the nut to the first fret...

I'm sure there is a logical explanation for this...

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This is a deep subject and one that has been covered in depth before.

You can start to get an idea of what is involved by reading THIS THREAD

Hope this helps!

Ken

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Reguards,

Ken H

Us beginners doo dat dat whey becoze it looks coul. Dats wye wii doo dat.

Ken, thanks for the links. I'll ponder it and hopefully I'll eventually understand - as Grumpy (aka Captain Helpful
) puts it - "wye wii doo dat".

The real reason for my question is that - of course - the bridge is glued on a little bit further north than I would like it. I'll go ahead and string this one up in a day or so and will post the results afterwards. I'll also see if my friends can pick this out acoustically...or if it just goes over their heads. I've got 2 friends who build and play a lot..so it will be really interesting to see if they can pick this out.

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You wouldn't need compensation if the string laid flat across all the fret tops and you fretted a note by pressing down over a fret rather than a space. Of course, you'd need to convince your string to vibrate in only one plane, as well.

So the answer is that it's to counter the difference between ideal and real string tension and vibrating length which had to be non-ideal because of string height above the frets which had to be changed to account for the uncontrollable vibrational plane of the string.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Remember, it not only has to do with the saddle position but intonating the saddle as well. You can get the saddle in the exact location but the guitar will still play out of tune if it's not intonated correctly. How wide is your saddle slot? If you can enlarge it more to the 'south' you can get the guitar in tune without anyone knowing any better.

Mike Doolin's articles on intonation can be found here.

Warning, this can certainly be a topic which becomes spirited during its debating.

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

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Sorry, I should have said this after the link in my last post.

Spend some time to educate yourself by reading the Doolin articles, it's a lot to read but really gives you the answers to your question and much more.

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

ya mean we don't do it because angled saddles look cool?

dang... more beginner's luck.


signed:

Capt. Helpless.













.

Grumpy, it must be terrible to find out you are just a beginner.  What will you tell your clients?  I'm depressed, and I am a beginner!    

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Nah, we just need more chisels...

Wonder how many sets and sizes we need to be master?

[QUOTE=grumpy] Us beginners doo dat dat whey becoze it looks coul. Dats wye wii doo dat.
[/QUOTE]

Cabin fever:n.
Boredom, restlessness, or irritability that results from a lack of environmental stimulation, as from a prolonged stay in a remote, sparsely populated region or a confined indoor area. Esp. prevalent in winter conditions when lack of daylight and cold temperatures prevail.

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Billy Dean Thomas
Covina, CA

"Multi famam, conscientiam, pauci verentur."
(Many fear their reputation, few their conscience)

The closer a string is to its maximum tension before breaking the less pitch change you get when you bend it. The string on a guitar that is closest to its breaking point is the high E. Thus the high E needs the least compensation. The other strings are all at less tension and, in general, there is less tension as you go lower in pitch.

The tension is based not on the guage of the string but of the core of the string. Therefore the wound G string is at a higher tension than the B string because the core is under higher tension. The extra mass that comes from the winding is what make the string have a lower pitch.

For the unwound B string the lower pitch is gained by adding mass the the string, That makes for a string that is considerably less close to its maximum tension and therefore needs more compensation. That is why you will see that the compensation of the B string if farther back than the rest of the strings.

Different brands and sizes of strings have different compensations. It is a good idea to compensate your saddle for a common brand and gauge of string and then re-compensate the saddle when the customer settles on the strings that he things work best.

Whassa cure?

[QUOTE=grumpy] Whassa cure?
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[QUOTE=Parser] There's one bit of guitar theory that I can't really get my head around and it has to do with saddle position. Conventional wisdom as I've learned it is that the distance from the nut to the middle of the saddle should be = scale length + about .125".

How can this make sense? The nut line and fret positions are all "perfect"...and then we just tack on this extra bit at the end? We certainly wouldn't want to tack on an extra 1/8" from the nut to the first fret...

I'm sure there is a logical explanation for this...


[/QUOTE]
Here's my understanding of this - at least the big picture. There are a number of good explanations for compensation and intonation that may say it better, but anyway, here goes...

If there was some kind of guitar string material that could be tightened to pitch - for any pitch - then all of the strings could have the same diameter and mass. If that was possible (it isn't), and you had a guitar where every string was identical, then the saddle would not be angled in the bridge.* So, the angle of the saddle is to compensate for the various diameters and masses of the strings. Fatter strings need more compensation. It might help you wrap your head around it better if you visualize the distances required to fret each note starting from the saddle, not starting from the nut. So whatever the correct compensation is for a particular string to create the correct note on the 12th fret, when you move down to the 11th fret, that compensation is still there, and on and on down to the nut.

Compensation gets you into the ballpark; intonation hits the home run.

Now that the saddle is placed correctly on the soundboard, with the saddle angle set to get very close to the correct amount of compensation, filing is done on the saddle to move that point back (towards the butt of the guitar) until the note at the 12th fret (fretted) and the note at the 12th fret (harmonic) is the same. Note that you can't easily add material to the front of the saddle, so your ballpark compensation (the saddle angle in the bridge, and where the bridge is glued onto the top) had better be very slightly too short, not too long.

I hope that helps! I struggled with the concept, and glued a bridge on at the wrong spot (too far forward), and was not able to file back far enough to get *perfect* intonation. So, I studied it some more, and hope not to make that mistake again.

This is definitely worth all the effort that you put into it, as it makes a huge difference in how well the notes sound up and down the neck, as well as open strings.

Also, let the guitar settle in, strung up to pitch and played for a while (a couple of weeks?) before you do the final intonation compensation.

*Note: "...every string was identical, then the saddle would not be angled in the bridge." - that is probably not 100% true, because tightening each of the identical (theoretical) strings to different pitches would probably require some small amount of saddle compensation for different pitches, but I think it would be very tiny compared to what is required for real strings with varying diameters and masses.

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Okay Mike,

With all that said and I think I'm tracking with you pretty good, my question is, how do you calculate compensation so you'll know what measurement to move the saddle.

I just learned something, I didn't know the saddle position for the B string was back farther than the rest of the strings.

 

Thanks Mike, that made this perennial question a little less muddy.  I will indeed read up on this.

[QUOTE=Papachulo]I just learned something, I didn't know the saddle position for the B string was back farther than the rest of the strings[/QUOTE]

Just to be clear B is not futher back than the rest of ALL the stings. but rather requires more compensation than high E or G. Low E is the longest string. It will intonate further back on the saddle but that saddle is further from the nut at low E than it is at B

Should have read


Just to be clear B is not futher back than the rest of ALL the stings. but rather requires more compensation than high E or G. Low E is the longest string. B will intonate further back on the saddle but that saddle is further from the nut at low E than it is at B

[QUOTE=MichaelP] Should have read


Just to be clear B is not futher back than the rest of ALL the stings. but rather requires more compensation than high E or G. Low E is the longest string. B will intonate further back on the saddle but that saddle is further from the nut at low E than it is at B

[/QUOTE]

Michael is right. The B string is not farther back than the rest of the strings. Just the high E and the G string. It might be a little forward or farther than the D string or about the same. Usually, the difference is within the thickness of the saddle. 3/16 saddles are nice in that you have lost of room for intonation.

[QUOTE=Papachulo]

Okay Mike,

With all that said and I think I'm tracking with you pretty good, my question is, how do you calculate compensation so you'll know what measurement to move the saddle.

I just learned something, I didn't know the saddle position for the B string was back farther than the rest of the strings.

Thanks Mike, that made this p<SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 'Times New Roman'; mso-fareast-font-family: 'Times New Roman'; mso-ansi-: EN-US; mso-fareast-: EN-US; mso-bidi-: AR-SA">erennial question a</SPAN> little less muddy. I will indeed read up on this.

[/QUOTE]

I find that moving the center of the saddle back .125" will almost always allow me to properly intonate. I don't remember the angle that I put my saddle at. I have it written down in the shop. Some builders measure the angle of the saddle and add the compensation in the middle. Others measure the compensation at the two E strings. It's two ways to get to the same thing.

The basic reason for compensating is not string stretch when fretting, but rather string stiffness.   Because of that stiffness, the actual point at which the string nodes occur are rather fuzzy; it is not at the nut or fret at one end and the saddle witness point at the other.   The string vibration is damped because of the break angle and the stiffness and so the string's hinge point at each end moves away from the theoretical nodes, and the higher the harmonic on the string, the further away from the theoretical nodes the hinge point appears.   Because of this, string harmonics drift ever sharper the higher up the harmonic series you go. The fatter strings are stiffer, and the larger diameter of the unwound B makes it stiffer than the typical wound G.   Hence the zig-zag compensation.   

String stretch does add to this issue, but it's not the underlying cause of the need for slanted compensation of the bridge saddle.

Ok, get a load of this...!

I ran the numbers for all of this. I built a spreadsheet to compare "stretched/fretted" notes with the "unstretched" notes (aka an action height of 0) at various positions on the fingerboard based on vibrating string theory. The spreadsheet takes into account the change in tension due to fretting a string, based on the height of the action at that fret, the fret, and the overall scale length.

According to this hurried analysis, saddle compensation is nowhere near as important as having a low action.

Here's a screenshot:


..and Here's a link to the actual spreadsheet, for those who want to mess with it. Only change the values highlighted in yellow....all of the other cells have formulas. Also, there are a bunch of hidden columns in here...feel free to unhide them in order to see more of the logic.
http://www.mediafire.com/?2gkulx3zm93

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[QUOTE=Rick Turner] The basic reason for compensating is not string stretch when fretting, but rather string stiffness.   [/QUOTE]

Thanks, Rick! (light bulb starts to illuminate a tiny corner of my brain.....).

That's the reason that changing string gauges pretty much always requires tweaking the saddle positions, while I've often gotten away with changing the string height (aka action) without changes to the string length ?

(This is on an electric- you can learn about this stuff a lot faster playing with a Strat knockoff instead of filing bone on an acoustic. On my 'list' is a testbed based on an electric-style bridge for getting the numbers before I do acoustic bridges...someday.)

John

One more thing...that spreadsheet does not compensate for an overwound string. It could, but it has been setup for the simple case of a plain string.

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