Development, evaluation, and validation of a high-resolution directivity measurement system for live musical instruments

Abstract

A measurement system has been developed to assess high-resolution directivities of live musical instruments. It employs a fixed, semicircular microphone array, a musician/instrument rotation system, and repeated note playing to produce 5-degree angular resolutions in both the polar and azimuthal angles. Its 2,522 spherical measurement positions reveal feature-rich, frequency-dependent directivity patterns. To date, a total of 16 wind and string instruments have been measured with the system. They were recorded as musicians repeated chromatic scales over standard working ranges following 5-degree rotations in the azimuthal angle, until a full revolution was completed. Directivity patterns of the first five partials of each note have been calculated and plotted as individual directivity balloons. While the approach provides high-resolution directivity results with reasonable numbers of microphones and data acquisition channels, it also has disadvantages, including lengthy recording and processing times. Special techniques have been developed to reduce the effects of nonideal measurement circumstances, including playing variances, musician movement, etc. A series of validation tests were performed using loudspeakers to simulate musicians under varying but controlled conditions. This presentation will discuss the methods and results of the work and provide comparisons to lower-resolution measurements.