Miscellaneous Topics
Intonation is Easy
Setting intonation generates a lot of questions online just as it generated a lot of questions decades ago when I was a teen-ager hanging around the local music store. Like many poorly understood subjects there is plenty of misinformation out there, probably more misinformation than solid, reliable, useful information. In spite of all the mystery, intonation is actually very simple and easy. Anyone that can accurately tune their guitar already has the skills needed to set intonation.
Why Does Intonation Have to be Set?
The answer is simplicity itself; strings raise in pitch when they are bent. That’s the reason intonation is a variable on your guitar. Most guitarists have bent strings sideways on purpose to bend into a higher pitch. It’s a staple of Blues, Rock and Country playing and has been for many years. What is less obvious is the fact that pushing down on a string also bends the string and raises the pitch. How much it affects the pitch is a function of two factors, the amount the string is bent, in other words how high the action is set; and the gauge of the string. The thicker the core of the string the more the pitch will increase for a given displacement. A wound string will intonate considerably flat compared to a plain string of the same gauge because it has a thinner core and the core of the string is what matters when it comes to bending and the effect on pitch. Believe it or not, if you understand everything written above you know enough to set intonation accurately and without a major hassle but just to make things easy I’ll go into greater detail about how to apply this knowledge.
The bottom line: Intonation is but one of many adjustments that allow a guitar to be used with various string gauges and various action heights.
How Accurate Does It Have to Be?
I’ve heard of people going to great lengths to get their intonation absolutely perfect but in my opinion it doesn’t pay to get too worked up about the issue. The reason is that the guitar, by its very nature, is not all that accurate. One of the hardest things to do when testing intonation is to press down the strings accurately without bending them sideways and affecting the pitch. When we are playing we are always putting a degree of sideward displacement on the strings. The pitch of any fretted note is bound to be less than 100 percent accurate.
Ditto for the frets themselves. Every few years I’ll see a guitar advertised with some sort of compensated fret placement that I designed for perfect accuracy but I’ve never seen any of these designs become popular in the marketplace. The fact is that guitars, along with most musical instruments are just not perfectly accurate devices. Beyond that, arguments regarding equal temperament have been raging for hundreds of years. Depending upon who you choose to listen to regarding the matter there are all sorts of different ideas of how musical temperament should be handled, the guitars you and I own are a compromise at best, as is every other musical instrument.
The bottom line: Intonation is important but perfect intonation is an impossible dream. Even if you accomplish perfect intonation at the 12th fret the variable introduced in normal playing will reduce this perfection considerably.
The Nut and Its Effect on Intonation
Guitars are for the most part mass produced products. Manufacturers have gotten very good at making instruments that satisfy customers with a minimum of specialized adjustment. A guitar being setup for the first time in the factory is given a conservative baseline setup and sent on its way. After being boxed, stored and then shipped to a dealer it can very well go through some changes as it settles into life as an instrument. For this reason the nut may be cut a bit higher than it needs to be and if the nut is too high the guitar will intonate sharp, especially on the lower frets. Working with nut slots is best left to someone that has experience in these matters or you can end up with a guitar that buzzes on the open strings and intonates flat. Frankly, I have the stock nut on most of my guitars, untouched since leaving the factory. They may be a bit sharp on the lower frets but it’s not enough to be bothersome. I would suggest that nut work be the last resort when dealing with intonation problems, something to undertake after everything else is sorted out.
The bottom line: If the nut is cut too high the lower frets will be sharp when the intonation is set properly at the 12th fret.
The Bridge and Its Contribution
The more a string is bent the more sharp it will sound. The higher the bridge is set the sharper the intonation. If you set the intonation and then raise the bridge substantially the intonation will become sharp. If you lower the bridge substantially after setting the intonation the intonation will become flat. It’s that simple. This can be useful in some situations. If you are setting the intonation and run out of travel within the adjustment range lowering or raising the bridge might give you enough extra range to save the day.
One big problem comes when the radius of a bridge does not match the radius of the fingerboard. If a 9.5” radius fingerboard guitar has a bridge with a radius of 12” the action will be lower at the center strings and higher at the edge strings. This plays absolute havoc on intonation settings not to mention making it impossible to set the action of the outboard strings as low as that of the center strings.
Bridges with individually adjustable elements for each string came along in the ’50s and were common by the late ‘60s. Gibson’s Tune-O-Matic was the standard most of these bridges were judged by but I noticed one other curious thing, some players got rid of their adjustable bridges and instead bought solid wood bridges, usually made of ebony. Some of these bridges had a degree of compensation built in.
As you can see from the picture this bridge is carved to be similar to an adjustable bridge that is setup for a string set with a wound 3rd string. As it is, installed on my archtop the intonation is close to perfect with a standard string set. There’s no special magic afoot here, as long as the ratios between the strings are fairly consistent and the bridge matches the radius of the neck accurately such an arrangement will usually intonate accurately. It doesn’t vary that much from guitar to guitar provided that the fretwork was done properly and that the nut was cut properly. You could take this very bridge off of the Heritage guitar it’s currently installed upon and move it to a Gibson, Gretsch or D’Angelico of the same neck radius and it would intonate properly. Solid bridges do a better job of transmitting vibration to the top of the guitar at the cost of individual adjustability. A well-designed one piece bridge that matches the fingerboard radius can eliminate the need for an adjustable bridge.
The bottom line: The higher the bridge the sharper the intonation. Bridge radius has to match the fingerboard radius or all other adjustments will be compromised.
String Gauge
String sets are fairly consistent from manufacturer to manufacturer. There’s a good reason for this, maintaining even string tension from string to string requires that the string gauge differ by the amount of pitch difference between strings. Strings that are tuned a 4th apart are roughly 13.3% apart in pitch, if you analyze most string sets you will see that the difference in string area (best measured in circular mils) tends to vary by 13% to 14% between strings. For the detail oriented among us I will add that the interval between the G and B strings, a Major 3rd, translates to a frequency difference of about 12.6%.
When it comes to the amount of pitch change when the string is displaced the core wire is what is being bent and that is what determines how much the pitch will change when it is bent by a certain amount. It is common for players to use solid third strings if they intend to do a lot of bending because using a wound third string will require much more of a bend than a plain string. In terms of setting intonation, if you replace a wound third string with a plain third string the intonation for that string will most likely be affected. As a rule, a plain third string will intonate sharp in comparison with a wound string. If you intend to substitute a plain 3rd string be prepared to try several gauges before you find the one that works. This is especially important if you are dealing with a one piece bridge that does not allow you to set the intonation for each string separately. With one-piece bridges string gauges can be used to fine tune intonation. Usually this happens at the 2nd or 3rd string. A little experimentation can do wonders.
The bottom line: The thicker the core of a string is the sharper it will intonate for a given string height. String gauge can be used as a way to fine tune intonation with one piece bridges.
Setting Intonation in the Real World
Somewhere in my teens I discovered harmonics, the ability to touch a string at a certain point and have it ring out a clear, sustained tone. Soon I realized that these harmonics where available at the octave (12th fret), at the fifth (7th fret) and at the two octave point (5th fret). If you chimed an octave harmonic and then played the fretted note at the 12th fret there might be a difference in pitch. By moving the bridge these two pitches could be synchronized and the intonation would be correct. Some people called this “setting the harmonics” but not even Einstein or Stephen Hawking can change the laws of physics and “set harmonics”. The harmonics are always correct; the accuracy of the guitar’s bridge placement is what is in need of adjustment.
So as a diligent teen-aged guitar nut I used to chime away and set the intonation by ear. This was before the days of inexpensive electronic tuners and the only way to be more accurate was to use a strobe tuner. Many music stores had one on site and they made easy money by setting intonation for customers eager to have accurate intonation. Meanwhile, kids that couldn’t afford to have it done at the store continued to do it by ear with highly variable results. Amazingly, decades later, with accurate electronic tuners, high quality guitars and years of experience it’s almost impossible to improve upon the way I set intonation back in the dark ages. It still is as much an art as it is a science.
The rules are still the same, if the intonation is too sharp move the bridge to lengthen the string and vice-versa. Before you even start thinking about intonation the action should be adjusted carefully and you should be certain that you are going to be satisfied with the way it’s adjusted.
The next step is to tune the open strings as accurately as you reasonably can. Tuning is also an art, but modern electronic tuners can make the task a lot easier. If you move the bridge itself in any way you need to re-tune the guitar before going forward. Keeping the guitar tuned is the greatest challenge of the intonation process. If you do this scrupulously the rest will come easy.
The rest comes down to measuring the tuning at the 12th fret in comparison with the open string. A good quality electronic tuner will do the job, even the old method of comparing harmonics to the fretted note can be surprisingly useful. In most cases this is how I set intonation and then I double check it with an electronic tuner when I’m finished. If a note is sharp, move the bridge segment for that string away from the nut, retune the string and check again. When both the open and the 12th fret note are in tune that string is intonated and you can move on to the next string.
For one piece bridges a good starting point is to set the high and low E strings, then check the strings in between. If the one piece bridge has compensation built in this may be all that is necessary. If not, try to find a close compromise. In most cases the second or third string will be the source of the trouble but you can obtain single, plain strings inexpensively if you find that this is what it takes to bring your guitar into intonation. If you find that one string is too sharp try a string of slightly smaller gauge, if it’s flat try a slightly larger gauge. I have four Gretsch electrics with one piece bridges and I can intonate all of them easily with standard string sets. I do substitute a plain third string for a wound third but I find that using a plain third string about .003” thinner than the wound string gives me even string tension and accurate intonation. I use Compton Compensated bridges on all of my Gretsch guitars. The compensation profile of these bridges is based upon the settings of an adjustable bridge with a standard set of strings. For me it’s the best of both worlds, the sustain and power of a one-piece bridge along with the accuracy of an adjustable bridge.
The bottom line: Setting intonation is not much more difficult than tuning your guitar. If you take your time and keep your wits about you it is well within the scope of anyone that can tune their guitar. Once you’ve performed the task of intonation a few dozen times it will become second nature and you will wonder why you ever thought that it would be difficult.
