Comparative analysis of the acoustical impedance of a set of traditional trombones versus P-Bone

Abstract

In this work, the impedance response of a set of trombones is analysed in order to find correlations between their sound and timbre and the main characteristics of the impedance curves. For this specific application, an impedance tube has been designed and manufactured to measure the different trombones' impedance curves. A plastic trombone (P-Bone) has been considered in the experiments to determine the importance of the material used to fabricate the instrument. In order to parametrise the trombones considered here, the instrument profile has been theoretically studied using a conical approach. More precisely, the tube and bell cone of the trombone has been discretised along its length in a set of small conical segments. Also, the influence of the mouthpiece is considered in the analytical formalism, and all these factors are optimised by employing a genetic algorithm to find the physical parameters that fit the experimental impedance curves. The experimental results are also compared with the opinions obtained from a survey about the subjective assessment of the same music passage recorded with the different instruments considered here. The results show that the impedance curve and some of the fitted parameters obtained correlate with the assessment of trombones in the blind survey. Moreover, the quality of the impedance tube here designed reveals that it is an excellent option to find leakages or dysfunction in this instrument.