Setting Correct Intonation on a Hollow-Body Guitar

[Ignatius]

Hey all--

 

A few folks from the old forum suggested that this entry from a while back is a useful way for newbies to understand correcting the intonation on an archtop guitar with a floating bridge (i.e., like an ES-125, ES-150, or any hollow-body guitar that lacks a mounted, stationary bridge). Just in case the original version gets lost when the old forum goes away, I thought I should post it here for future reference:

 

In any case, your guitar--if it is a hollow-body archtop of the ES-125 sort--has what is called a floating bridge, meaning just what you said: it is not attached to the guitar body, but it instead "floats" around wherever you want it and is held in place by string tension. The bridge can only be placed in one place on any given guitar, but that place is unique to each guitar: it has to be set so that the harmonic chimed on the twelfth fret is in tune with the note played on the twelfth fret. (Of course, it is roughly the same place on all given guitars of a certain model, but each guitar has a unique sweet spot where the harmonics and notes at the twelfth fret match just right. Also, it is a given that the bridge must be someplace where the strings run straight in line with the neck of the guitar; don't move the bridge accidently too far to the left or right.)

 

To do this, place the bridge about where you think it needs to go. On some old guitars like mine, there is a lot of scuffing and minor scratching in the area where it used to be. Then restring the guitar and start tuning up: once the guitar is in tune, check the note and the harmonic at the twelfth fret. Start at the first and sixth strings: once the two ends of the bridge are in place, the rest should be close to proper intonation as well. You will need to loosen the strings in order to move the bridge, and only move it a little bit at a time if the harmonic and the note are close. Then tighten up the string or strings on the side of the bridge you are adjusting and check the harmonic and note at the twelfth fret again.

 

It can be done by ear if you have a good ear and patience. It is easier if you have an electronic chromatic tuner that shows flat or sharp and can pick up the harmonics as well. I have a cheap Dean Markley tuner that came with a set of strings once, and it does the job just fine.

 

If the note is sharper (higher in pitch) than the harmonic, move the bridge down toward the tailpiece. If the note is flatter (lower in pitch) than the harmonic, move the bridge up toward the neck of the guitar. When you move the bridge, move it one side at a time, and work on getting either the sixth or the first string set first. When I say move the bridge, I am talking about moving it a sixteenth of an inch or so at a time. This is a time-consuming process so you need to give yourself a long time and a lot of breaks the first time you try this. It can be very frustrating at first, but as your ear develops, it gets a lot easier.

 

Two last notes. First, it is a lot easier to check and correct the bridge intonation when you are changing strings. Then, the bridge already is in roughly the right place, and you will find it easier to tweak the bridge movement because you could check the intonation on, say, the first string when you take the second string off to change it, and so on. Second, you may end up with your bridge at an angle. Not all guitars end up with the bridge perfectly straight across the body of the guitar. Sometimes, the bridge may have one end (typically the lighter strings) higher than the other end. No problem with that.

 

Oh, and of course, changing the height of the bridge will also affect intonation. If you lower the action of the strings, you may find that you need to re-do your intonation. You also will need to re-do intonation if you switch from light to medium strings and vice versa. All in all, if you can't get your archtop guitar to sound properly in tune, the bridge probably is misaligned. If all this sounds bewildering, it may be worth spending the money to have someone set up the guitar right the first time and then you learn by trial and error on a guitar that already is close to correct in its intonation.

 

I hope this helps!

 

Oh, and for all you other posters who have offered helpful semi-hollow and hollow-body advice back at the old forum, maybe now would be a good time to repost that information here, perhaps with a more clear heading so the forum becomes a more easily searched resource.

 

Let's keep the hollow-body forum rolling!

 

Ignatius

[jmendoza]

One thing I have noticed missing from almost every article on setting up a floating bridge on an archtop that is crucial is the angle of the strings. You need to have the string angle in front of the bridge (towards the neck) and in back of the bridge (towards the tail piece) equal. A quick check can be done to see if the bridge is leaning towrads the neck, as this is what usually happens from tightening the strings during tuning. A bit of pencil lead or graphite in the string grooves of the bridge is helpfull to keep the strings from pulling the bridge towards the neck while tuning, and also while aligning it fore and aft. The first thing to do is to get the bridge standing straight up and perpendicular to the top, such that the string angle is eqaul on both sides of the bridge because this adjustment affects intonation. Once you start moving the bridge to intonate it, double check that the bridge is not tilted towards the neck or tail piece, and the string angle remains equal. Some of these adjustable bridges have the adjuster studs screwed into the base (part with the feet) at an angle, so be sure yours did not get turned around backwards accidentally when someone removed the bridge and took the saddle off of it.

 

The reason this is so important is because archtops derive their tone and volume from the downward pressure the strings exert on the bridge. If the bridge is not sqauare with the top, and the string angle over it is not equal, it reduces the maximum force being exerted on the top by the string and therefore you lose volume and tone. This is a very common problem with the violin family that somehow gets overlooked in archtop guitars. In severe cases, you may have to re-fit the feet of the bridge to the guitar's top, but usually there is enough clearance in the bridge saddles' two holes that go over the height adjusting studs to allow it to be moved and adjusted. If you find the holes in the saddle for the adjuster studs are too big and allow the bridge to tilt, then you can bush them with a short section of brass tubing to correct the condition, or replace the bridge/saddle.