THEORETICAL AND EXPERIMENTAL INVESTIGATIONS OF THE BEHAVIOR OF BOWED STRINGS UTILIZING A MAGNETIC PICKUP SYSTEM

Abstract

Pickup systems for musical instruments generally serve the purpose of improving the perceived quality of instrument sound through appropriate amplification of electrical signals. While different pickups like a microphone or piezoelectric pickup are common to many string instruments, magnetic pickups are mostly used for plucked string instruments like the electric guitar or electric bass guitar. For a bowed instrument like a violin, microphones and piezoelectric pickups are commonly used, but magnetic pickups (which convert mechanical oscillations of a magnetized string to oscillatory changes in magnetic flux, manifesting in changes in voltage) are rarely used. The primary objective of this work was to establish foundational insights for new designs of magnetic pickups for bowed instruments like the violin. A secondary objective of this work was to motivate a modified damping factor term or modified external force term associated with dampening of vertical bowed string motion based on experimental evidence. To achieve these objectives, a new experimental setup was considered for exploration of the behavior of a bowed string-magnetic pickup system, specifically examining maximum and average voltage outputs across different frequency distributions, magnetic flux densities and their evolution over time for different rotational positions of the magnetic pickup about a magnetized, monochord string. Validation studies showed that the findings were consistent with expected results from tonal theory and literature, based on analysis of frequency spectra, voltage output (both obtained from magnetic pickup and optical switches) and magnetic flux densities. Based on the new experimental setup, an optimal position of the magnetic pickup was determined according to selected performance criteria. This work showed ample experimental evidence demonstrating the prevalence of significant damping of the vertical string oscillations by the combination of the presence of bow hairs at the point of bow-string interface and the downward bow force applied. Based on the insights and findings of this work, new and advanced designs of magnetic pickups for bowed string instruments could be achieved.