The G string, or the third string of the classical guitar, is the thickest of the treble strings. It is more prone to string buzz. There are a few reasons why it happens and the solution directly depends on which of the reasons caused it in your case. While cheaper and beginner guitars are more likely to have the G string buzz, I have seen it happen on $2,000 guitars too.
The easy reason to discount is the playing technique. If you’re a beginner and are playing only in the first position like all of us once did, the irony is that the biggest finger stretches happen on the fingerboard in that beginner position. So the fingers will often fall in the middle of the frets rather than against the fret wire which is the proper technique. Result: string buzz, as the string – any string, not just the G string – doesn’t quite clear the fret ahead and vibrates against it.
Assuming improper playing technique is not causing it, the most common causes for string buzz are low action, uneven fret heights, a poorly fitted nut slot, loose tuning head parts or a bowed neck. Any of them alone can cause string buzz and often they occur in combination.
Improper distance between frets used to be an issue on older generation classical guitars. But today’s factory-made guitars are built to machine precision widths and distances, so we can mostly rule this out as a cause.
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Most likely cause: low action (and what to do)
‘Action’ is the tiny distance between the fretboard and the strings. It is around 3 mm for the first string (generally) and 4 mm for the sixth string. If this distance gets lower, the action is said to be low and the vibrating string comes in contact with the fret(s) to generate a fret buzz. With the G string being the thickest, the problem can be acutely felt here. This sort of buzz goes across the entire length of the board, as against an isolated rattle emerging at the first few frets.
To clear up fret buzz, your first move should always be to replace the strings with a fresh set – this often clears things up immediately. You can, in particular, try a new set of nylon strings with a thinner carbon G string – check the Savarez 510MR at Amazon – it has the top two strings in nylon but the G string is carbon.
Your guitar may have a tendency to react to the climate, which can sometimes cause the woods to slightly move, altering the original setup. This is not unusual if you live in a place that sees huge variations in humidity throughout the year. Inserting two stacked quarters between string and fret is a good test – the height of the coins is about 3.5 mm, which means the action is in the ballpark. Any less of a distance should be corrected.
Action can be raised by means of a truss rod if your guitar came with one – Cordoba models almost always have a truss rod. Raising the saddle can also increase the action, usually done with added buttressing under the saddle. We’re talking millimeters here so even a little added thickness with folded paper or cardboard stock at the bottom helps a lot. Any music store or qualified technician can do this for you if you are uncomfortable doing it yourself.
Ensuring that your guitar is being properly humidified will keep it in good condition throughout the seasons. If you want a primer on action on the classical guitar, read my article Classical Guitar Action to get to grips with the basics and its importance to the overall tone of your guitar.
Uneven fret heights, a common issue that needs fixing
Fret misalignment is a problem that occurs often. The frets are normally placed in a consistent plane. If one fret is too high, it can cause the string to come into contact with that fret when playing the note one-half step below. Again, the thicker G string may suffer because of this.
The problem may not be obvious with stationary strings but when a string is plucked and set in motion, the oscillations travel up and down in relation to the fretboard. Depending on how hard the strings are set in motion (and how much the fret misalignment is) the vibrating motion can bring the string(s) in contact with the fret wire for an unholy buzz. The buzzing sound usually occurs further up the fingerboard from the fretted note.
Because different strings behave (oscillate) differently on your guitar, here too the first tip to try is to change your set of strings. This simple solution is so often the correct answer! A new set often gets the sound under control. Again, a thinner carbon G string may be just the way to go.
Uneven fret height effectively changes the action of the guitar for the worse. To check for unevenness across 3 frets, place the edge of a credit card down on 3 adjacent frets. If it sits well and proper, touching all 3 frets evenly, all is good. If the card wobbles to the right and left then the center fret is a little too high.
Poorly leveled frets cannot be corrected at home easily, at least for most players who are not comfortable with woodworking. You will want to send it in for repairs. It is not an expensive thing to get done and will be covered under your warranty if yours is a relatively new guitar.
Poorly fitted nut slot: How to identify and correct it
If your G string buzzes as an open string, the problem is the nut height. Once you place your finger on any fret and the buzz goes away, it can only mean that the nut height is too low and the string is touching the first fret or two. Many players like the nut height set very low, especially if they are coming over from the acoustic/electric world.
Even if the strings clear the first fret there can be a problem called ‘back buzzing’. This is the buzz that happens behind the fretted notes (toward the headstock or nut). If you play the A chord on the fifth fret, and if you hear a rattle behind the fretted hand towards the headstock that is ‘back buzz’. Back buzzes occur when the string vibrates against the frets between the fretted note and the nut.
In either case – an open string buzz or back buzz – you have to raise the nut height. Similar to the saddle solution above, you can buttress the nut slot for added height. It is a low-tech solution but it works. You can use bone dust or baking soda with super glue to increase the string height in the nut slot. Or you can shim the nut from below with folded paper or cardboard stock.
Perhaps the best solution is to fix a new nut! It is hardly among the more expensive parts of your guitar.
Loose guitar parts rattle (Stop them)
This is probably the most intuitive cause to understand as well as fix. Stuff rattles because some other stuff in the vicinity has come loose.
Almost always, these sounds can be located in the headstock area of your classical guitar. Use your hand to dampen what may be a loose part. Check the simplest possibilities first, like a loose tuning machine screw, or a string end vibrating against the guitar. Guitars buzz in some strange places and may take some poking and prodding to locate.
Just touching a knob or a capstan roller can make the buzz go away sometimes. Removing the tuner mechanism and screwing it on again carefully and securely is the solution. A syringe injection of glue at the right joint or two is also known to help.
Bowed guitar neck, relatively rare but it happens
Even though we say the neck of a classical guitar is straight, it usually has a gentle ‘curve’ in the middle between the first and twelfth frets, dipping ever so gently somewhere between the 2nd fret and the 8th. Placing a straightedge over the length of the fingerboard will reveal this ‘dip’ or ‘relief’.
When the neck is concave or bowed forward in its alignment, the action at the bridge must be lowered. As the strings are lowered the strings get closer to the frets further up the fingerboard. This proximity will cause extra fret noise – due to the low action that we know well by now.
If the neck is convex or back bowed, the action must be raised to keep the string’s proximity acceptable in the central part of the fretboard. Generally speaking, an attempt or two at adjusting the truss rod (if you have one) is all you can do to restore normalcy. Otherwise, anything to do with a relatively serious issue like a bowed neck should prompt a visit to the store or a technician.
Or if the guitar is new, it’s time to send it back and ask for a replacement. You really don’t want to be dealing with bowed necks on your own.
On a related note, if you’re among those who have a totally different issue with the G string, you should check out my article Why Does the G String Sound Tubby and get some good information to tackle that.