Experimental tests of free reed instrument simulations

Abstract

Recent simulations using finite element software have been used to study the fluid dynamics, pressure acoustics, and structural mechanics couplings involved in self-sustained reed oscillation and reed-pipe coupling in free reed instruments. This paper reports on two experimental studies related to these simulations. One of these involves reeds of the type used in harmonicas and accordions. The results verify that the assumed dependence of sounding frequency on blowing pressure, which has long been used as a benchmark for a successful simulation is correct for blowing pressures close to those normally used in playing the instruments. At higher pressures, however, a variety of anomalous results can occur. The second study involves finite element models of pipes from the free-reed Asian khaen. Pipe simulations produce results for the input impedance of the pipe that agree very well with experimental measurements. A pressure acoustics model of the khaen pipe coupled to a free reed produces results that appear realistic for sound radiation but does not realistically capture the mechanism of the self-sustained oscillation of the reed driven by airflow. Measurements in the current study show that this model does provide approximate quantitative agreement with the predictions of the simulation.