How to Know If False Strings Are Hurting Your Sound

Once a common problem, false strings still occur and can make your instrument sound out-of-tune

YI_Tao

Acoustician and string developer Fan-Chia Tao.

One of the most common questions about stringed-instrument strings is about the nature of false strings. What is a false string? Musicians often use the term to describe any string that does not sound right, such as a string that sounds dead or won’t bow properly. However, a false string technically occurs when a string doesn’t produce the correct pitch due to a lack of uniformity or defects. In rare cases, the instrument itself may be the source of intonation issues.

To understand false strings, it helps to understand a few basic concepts. When we talk about uniformity, what we mean is that the string is not what physicists call an “ideal string.” An ideal string is uniform in density and mass along its length and is completely flexible. This ideal guides the choices that string designers make with materials and varieties of string design.

Corrosion & Conformity

False strings were more common when gut was the primary string material. Gut strings are a natural product made from highly processed sheep intestines and, like other organic materials, it is subject to variations in temperature and humidity. Thanks to modern production techniques and materials, like metals and synthetics, false strings are less common. However, strings can become false with use, through rusting and corroding from the inside or by players damaging the winding by pressing them down too hard on the fingerboard. In areas where damage has occurred to the string, rosin, sweat, and oils can get into the windings, accelerating corrosion and creating non-uniformities.

For any given length, a string will vibrate naturally at many different frequencies. The fundamental is the lowest natural vibration frequency and the higher natural frequencies are the overtones. If the overtone frequencies are exact multiples of the fundamentals, then they are harmonic. For example, if we play a cello’s open A string, the fundamental frequency is 220 Hz (the abbreviation for Hertz, the technical term for vibrations per cycle), and the harmonic overtones occur at 440 Hz, 660 Hz, 880 Hz, and so on. However, the overtones of a vibrating string are harmonic only if the string is completely uniform throughout its vibrating length.

Perfect Harmonics

Another requirement for perfect harmonics is that a string be completely flexible. If a thick string is made from a large, solid piece of material, it will be stiff and its lack of flexibility will cause the overtones to become progressively sharp. Fortunately, this is not a significant problem with most modern wound strings, where the windings give the string extra mass, while keeping it flexible.

Our Western (as well as much non-Western) music and harmonic language is dependent on overtones being harmonic. A plucked string vibrating with non-harmonic overtones can sound out of tune. Non-harmonic overtones can also cause problems with bowed strings, which vibrate differently than plucked strings. As you draw rosined bow hair across a string, it forces the string to vibrate with harmonic overtones in a sawtooth waveform. This behavior is called the Helmholtz motion, after the 19th-century German physicist who first described it. If the string does not naturally vibrate harmonically, it can slow down or interfere with bowing response. In extreme cases, the string will not bow at all.

In a perfectly uniform string, the frequency of vibration is inversely proportional to the vibration length. So, for example, a uniform string will vibrate exactly one octave higher if you divide the string in half, a fifth higher if you divide it in two-thirds, etc. Some players test for false strings by playing fifths on adjacent strings, but this procedure is unreliable because it requires both strings to be uniform and for the player to accurately stop both using her fingertips. Some players use an artificial aid, like a matchstick, to stop both strings accurately, but even this method is not completely reliable because the instrument itself can cause imperfect fifths.

The alignment of the nut and bridge, as well as the deflection of the string when pressed onto the fingerboard, can lead to false-sounding strings or imperfect fifths. Guitar makers go to great lengths to adjust the nut, bridge, fingerboard, and frets to compensate for these effects. Violinists, whose instruments lack frets, have a much greater tolerance for such problems, though it helps to have everything adjusted as carefully as possible.

The Impact of the Instrument

The instrument itself can also cause imperfect fifths and intonation problems. The body of an instrument has its own natural modes of resonance, which can detune a string—almost a quarter tone in some cases. It’s even possible for the instrument’s resonance to prevent the string from vibrating at exactly the desired frequency no matter where you stop the string. The extreme example of this phenomenon is the wolf note, which occurs when the played note matches the instrument’s resonant frequency. This effect produces a sustained harmonic overtone that is so strong that the string can’t vibrate correctly when bowed.
Another method used to detect false strings is to listen for a pitch change after the bow leaves an open string. This method can also lead to an incorrect diagnosis of a false string because the instrument’s resonance affects the sound’s purity, which affects your pitch perception. How you hear pitches is dependent on volume, so as a note decays, the perceived pitch can change even if its frequency stays constant.

How to Detect a False String

There is no simple, foolproof way to detect false strings. However, some commonsense procedures can help narrow down the cause. The first step is to replace the suspected string with another string of the same type. If that fixes the issue, the original string was the problem and is a false string. If you suspect a brand-new string is defective, and replacing it doesn’t solve the problem, try a string from a different manufacturing date (since strings made at the same time may share the same defect) or a different brand. If the symptoms do not go away, the instrument is the cause. If the string has only recently become false and replacing it doesn’t solve the problem, the instrument may have gone out of adjustment.

Finally, the sound of a string does change with time, and some strings will change much more so than others, without necessarily causing intonation problems. Many variables can determine string life, including string construction, materials used, frequency of use, and a player’s sweat chemistry, so that predicting a string’s lifespan is difficult. Some players replace their strings every few weeks while others play happily for years on the same set.

The only hard and fast rule is: if your string changes for the worse, consider changing your strings.

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*This article appeared in Strings June 2011
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