Diagnosing dead spots of electric guitars and basses by measuring the mechanical conductance

Abstract

The ‘‘sustain’’ of the string signal is considered as a quality attribute of an electric plucked instrument. In musical practice, distinct locations are observed on the fretbroad where a string decays faster than at adjacent frets. Such ‘‘dead spots’’ originate from the fact that the string may cause the neck to vibrate. Energy flows from the string to the neck with the consequence that the string vibration decays irregularly fast. Experiments were performed with the aim of finding a measuring approach for the diagnosis of dead spots in terms of the vibration willingness of the neck. Various parameters (decay rate, surface velocity, admittance) were ascertained for a series of electric guitars and basses. Special care was taken to ensure comparable and ‘‘natural’’ boundary conditions. Measuring the mechanical conductance (i.e., the real part of the point admittance) on the neck with the instrument held in normal playing position proved a straightforward and reliable method for the diagnosis of dead spots. The measuring procedure and instrumentation will be presented. Typical results will be given in a compact 3-D representation (conductance versus frequency for each fret), evaluated and related as well to the decay rates as to the vibrations of the instrument body.