The vibration of strings
is placed alongside the string so that the field is perpendicular to the string. Lorentz force will result from the current interacting with the field, creating an oscillation. This will then generate an EMF by Faraday's induction which can be measured. To measure the voltage, there must be two distinct ADCs for the left and right channels (Or there will be a shift different between V1 and V2).
By changing the frequency of the excitation signal, a graph could be produced, plotting frequency against normalized
amplitude (Vs/ VI ), Vs being voltage proportional to the speed (measured in the experiment) and VI (V = IR), varying the current will let us compare the effects it does to the movement of the string.
Results
From Marcello Carla’s result, several measurement series have been obtained varying the sweep time (from 30 s/Hz to 240 s/Hz), the frequency interval (from 4 to 10 Hz around the string resonance) and the current level. As seen in this figure, the lowest current values lead to a classical symmetric bell- shaped curve for the amplitude, while the phase follows the usual S-shaped curve. As the current level increases the shape of the curve changes; the peak becomes lower and moves rightward, and a hysteresis loop begins to appear. The hysteresis loop widens as current increases further, with the upper branch traversed during the upward frequency sweep and the lower branch traversed during the downward frequency sweep. From these data, it is quite clear that effects described in the amplitude equation are present in the resonance of the guitar string.
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