About once a week I get an e-mail from someone who wants to know how to build a banjo that has no overtones. This is impossible. Here's why.

To the rest of the musical world, other than bluegrass musicians, overtones are the natural harmonics that occur when an object vibrates. For columns of air (such as what you find in flutes, trumpets, trombones and organ pipes), strings or metal bars, there is a series of overtones that follow a specific mathematical sequence. It is the combination of these overtones that gives each instrument its unique voice. The only tone that has no overtones is a sine wave. A softly blown flute produces a sound similar to a sine wave.

A clarinet produces a sound very much like a square wave.

There are many different wave forms produced by different instruments, and they can generally be described as combinations of sine, square, triangle and sawtooth wave forms. These forms are named after the shape they produce on the face of an oscilloscope.

A banjo with no overtones would sound like a plucked flute. It would be dull, bassy and have no richness at all. What we bluegrass musicians are bothered by are extraneous sounds. "aftertones" or sympathetic vibrations.

These sounds can be any of several different things or a combination thereof.

One of them is sympathetically vibrating open strings. For example, if you play your open third string in G tuning, sometimes your fifth string or your first string may begin to vibrate also. This can be caused by having a component, such as a bridge or the head, itself, that resonates at the frequency of the string that begins to vibrate. The solution may be to adjust your coordinator rods, check your head tension or replace the bridge. Submerged wood bridges seem to alleviate this to a certain degree.

Some tone rings are very prone to this kind of sound. One solution for this is to adjust the head tension to a different setting. Another approach is to use a submerged wood rim.

Sometimes the small string segments between the tailpiece and the bridge are the culprits. You can check this by playing something that causes the sound you hate, and then damping the short string segments with your right hand. If this stops the sound, weave a bit of felt in and out of the string segments between the tailpiece and the bridge.

See if the armrest is the source of the problem.

Loose brackets can cause this sometimes, also.

One other contributing factor that cannot be overlooked is your own playing technique. The closer you play to the bridge, the more nasal sounding the banjo will be. It becomes harsh and brilliant. Moving your right hand closer to the end of the fingerboard will alleviate this to a certain degree. Similarly, I have noticed that people who move their picking fingers with economy of motion generally have a better tone than those who don't. Make sure your fingers don't flounder and flop about when you are playing.

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