Intonation Check

Here is an interesting question received by email:

Roger, I see your posting on Deja news from time to time where you will respond to questions about other luthiers or guitars. I was wondering if you would answer a question for me. In looking at two of my guitars, a Takamine C136S and an Amalio Burguet 1A, I noticed that on my Burguet that the saddle is inserted at a very slight angle where the Takamine is square to the bridge, and I was wondering why? The Burguet cost quite a bit more and is a much better guitar but that doesn't explain why it differs from my Takamine.

Thanks in advance for your consideration in this question.

Douglas G.

Answer:

This is a good question, especially since you have observed a difference between your instruments which made you curious.

The slight angle is to help with intonation problems created when the string is pressed down to the fret; the added tension causes the pitch to rise. Since the bass strings are set higher they require more compensation, thus the saddle angle in that direction. Actually each string should have a unique individual saddle placement, which explains the compensation notching in guitar saddles and the complex electric guitar bridge designs. Low tension nylon strings by nature don't go sharp as readily as stiffer steel strings; therefore, the compensation is even more important for steel string guitars. For nylon guitars I find that either system, angled or straight saddle, is adequate (but never perfect) so long as the bridge is glued down in the correct location.

The fret scale is an ideal mathematical progression. The expected bridge saddle placement would be the distance from the nut to the 12th fret times two. But, since the strings are above the frets and will rise in pitch when pressed down, the expected placement is not quite correct. To compensate, the saddle (on a nylon string guitar) is customarily moved back an additional 5/64" from the ideal, mostly to fix the 6th and 3rd strings which are the most sensitive (because they are thick) to going sharp. The angled saddle is an attempt to further refine the compensation by slightly lessening the compensation on the treble side (which are usually closer to the frets) and slightly increasing it on the bass side (where the strings are usually higher from the frets).

As a test, string both your instruments with identical sets. After the strings stabilize use a sensitive electronic tuner (chromatic) to test various notes: the high to the low on an individual instrument and then between the two guitars. First check the 1st and 6th strings at the nut (open position) and 12th frets to see if these notes are in tune. If so, then the bridge is generally glued in the correct location on the soundboard. Then check open notes, low notes and high notes on all strings which should all register in tune. If, for instance, the high notes consistently read sharp across all strings then your bridge placement may be fautly. If one string gives inconsistent readings then it may be defective (also termed "false") and should be replaced. With matched true strings your guitars will perform identically but, if the bridges are placed differently by the manufacturer there may be a discrepancy.

Both your classical guitars represent differing philosophies about the necessity of compensating for string tension. The fact that both guitars will perform satisfactorily if the bridge is correctly placed demonstrates that neither system is critically important. Bridge placement is just one of several related factors of equal validity: high quality strings, correct action adjustment at both the nut and saddle, accurate fret placement, correctly milled frets to remove wear marks and grooves. If all the necessary factors are coordinated the instrument will tune accurately.

Article:

Using an Electronic Tuner to Check the Guitar's Bridge Placement

This method works best with a chromatic tuner and assumes that the string height settings are correct at either end of the scale. Install new strings, allow them to stretch naturally, and then carefully tune the guitar.

I. For each string, tune the open note and then check the 12th fret harmonic (if using a chromatic tuner you can also check fretted notes at the 15th or 16th frets). These notes should read true without retuning. (If the open note and harmonic do not match the string may be false or distorted and must be changed.) Next, check the fretted 12th fret note against the open string.

A. If the fretted note is sharp the bridge needs to move back to lengthen the string.

B. If the fretted note is flat the bridge should come forward, shortening the string.

C. If the fretted note is in tune then the saddle placement is correct.

II. For a classical guitar with nylon strings there may be a discrepancy between the 3rd and 4th strings.

A. The thick nylon 3rd string is problematic and tends to go sharp more than the 1st or 2nd strings. The 3rd string is also has the least tension, another contradictory factor leading to intonation problems.

B. The adjacent 4th string is thin but has the most tension. It therefore behaves quite differently from the neighboring 3rd string.

1. The result is frequent tuning problems generated by the contradictory intonation tendencies of these two adjacent strings.

C. Determine that the 1st and 6th strings indicate the overall bridge placement is correct. If so, then the saddle itself can be specially compensated to offset the natural conflict between the 3rd and 4th strings on the classical guitar.

1. If the 1st and 6th strings are showing a discrepancy which is not likely caused by faulty strings then the guitar should be taken to an experienced luthier for further checking.

a. Bridge relocation or saddle slot rerouting may be necessary.

III. The steel string guitar has intonation problems between the plain 2nd and the wound 3rd strings.

A. The thick plain steel 2nd string tends to go sharp more than the 1st and the 3rd.

B. The thin wound 3rd string only needs slightly more compensation than the first.

C. If the 1st and 6th strings read very close to true then a compensated saddle will help resolve the intonation conflict between the 2nd and 3rd strings.

1. Do not check individual fretted notes at a position with obvious playing wear into the fret. This wear will affect the accuracy of the reading.

IV. The electric guitar has intonation problems between the thick plain steel 3rd string and the thin wound 4th string.

A. Most electric guitar mechanical bridges have individually adjustable saddles to facilitate precise tuning of each string over the entire fret scale length.

1. Sometimes incorrect bridge placement limits the travel of individual saddles and prevents completely accurate intonation.

a. Relocation of the bridge may be necessary.

B. If the 1st and 6th strings can be tuned via the individual saddle adjustments then the entire bridge placement is correct and each string can be compensated for perfect intonation.

Let me know what you think about my page. Send mail by clicking here.

]

All material on this this website is protected under international copyright law and as such is prevented from being used for any other purpose without express written approval

Thurman Guitar & Violin Repair, Inc.
900 Franklin Av.
Kent OH 44240
Toll Free: 888-803-8693