If the tension of the strings is changed by scordatura, the outcome depends on the extent of the detuning. Slight decreases in tension increase overtone content since, relative to the new lower fundamental, the frequency of the highest possible overtone increases. However, if the tension is decreased further, overtone content is restricted by the slackness of the string, encouraging damping. Eventually, the string becomes difficult to control and responds slowly to excitation, especially bowed articulation. Increases in tension by scordatura are limited because the string is liable to break under high tension. However, slight increases in tension have the effect of detuning the upper partials and making the string less responsive to excitation, particularly bowed articulation.
As a string is tuned down, its tension decreases. Small decreases in tension might at first strengthen the overtone content slightly since the frequency of the highest contributing overtone, set by string width and other factors, stays constant for a decrease in fundamental pitch. However, further decreases in tension weaken the potential overtone content of the string; the less tense string is shaped less sharply at the bridge and nut and more energy is lost to damping as vibration is reflected in these regions. Therefore, for a fixed contact point, the timbre is less overtone-rich and the scope of sul ponticello sound is reduced. For small decreases in tension by scordatura, the string is easier to set into motion. Therefore a relatively ‘normal’ sounding tones is possible under low excitation forces, flautando and overtone-takeover effects are more difficult to produce. As tension becomes very low, the vibration of the string is made up of much torsional movement, causing the string to respond slowly to excitation. This causes some irregular pitch changes and a noise component in the sound. The scope for varying plucking/striking force and bow speed/pressure is reduced, particularly at the upper end of the scale, and loudsounds are unsustainable. For high excitation forces the string often strikes the fingerboard during vibration. Eventually the string becomes too ‘floppy’ to sustain transverse vibration. The lower strings are first to be effected by torsion since their increased width increases the propensity to vibrate in such a way.
As tension increases above ‘normal’ tuning, the sound becomes slightly louder since the string exerts an increased force on the bridge; the coupling between bridge and body is strong. Higher partials become weak and out of tune with the fundamental due to string stiffness. Vibration becomes difficult to control, particularly in bowed sound. Rapid bow changes are difficult as the string is very sensitive to changes in plucking/striking force and bow speed/pressure. Longitudinal vibration of the string might be heard in the form of high-pitched squeaks.
If the tension of one string increases or decreases significantly, the corresponding change in down bearing force on the bridge affects the amplitude of the other strings. The amplitude of the other strings increases and decreases in inverse proportion to tension.