Tuesday, March 23, 2010

String Tension Terminology

Players, violin makers, and scientists all use the same term tension to describe slightly different things. This can sometimes lead to confusion.

When scientists and engineers discuss tension, they mean the pulling force exerted along the length of a string. This is what we specify in our catalog and website. This force is determined by the amount of mass (material) on the string, the tuning (frequency at which the string vibrates) and the vibrating length of the string. For standard instruments and tunings, the string vibrating length and tuning are fixed. So the only variable that the string designer can change to affect the tension is the amount of material on the string. The more mass, the higher the tension.

When instrument makers discuss tension, they usually mean the force exerted by the strings on the top of the instrument. This force is determined by string tension as well as the geometry of the bridge and the instrument. For example, the flatter the string angle over the bridge, the less static vertical force the strings exerts on the top of the instrument. Most makers believe this force can significantly alter the sound and playing characteristics of the instrument. I’ll discuss this topic in a future post.

When players discuss string tension, they mean the subject feeling of the string from both their left fingering and right bowing hands. While this subjective feeling of tension is largely determined by the string tension, it is also affected by other factors including string response, string sound, core elasticity, the diameter of the string, etc.

Another confusing term is string gauge. Gauge refers to the diameter of the string, not the tension. In the gauge system most commonly used for gut strings, the diameter in millimeters is equal to the gauge times 0.05. For example, a 14 gauge string is equal to 0.70mm, or 0.0276" in diameter. For guitar strings, the gauge most often refers to the diameter in inches or thousands of an inch. So a 36 or .036 gauge string is 0.036" in diameter.

For an unwound string (or simple guitar strings with one type of winding), larger diameters lead to more mass and therefore higher tension. However, modern bowed strings are wound with multiple windings of different materials with different densities . Therefore, a larger diameter string may not be heavier tension. That is why bowed string manufacturers specify the tension rather than the diameter or gauge.

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