Source characterization of a ducted source using acoustic free velocity

A common method to characterize linear time invariant ducted acoustic sources is the electroacoustic analogy. The sources are typically defined by their internal source strength and source impedance. Various methods have emerged to determine the source characteristics, broadly categorized into direct and indirect methods. Direct methods involve using a secondary source with significantly higher amplitude to measure source impedance, but those methods are unable to determine source strength. Indirect methods vary acoustic loads to obtain both source strength and source impedance, but accuracy depends on appropriate load combinations. In this research, we propose an inverse method to determine the acoustic source strength from the measured acoustic transfer function and the operational acoustic pressure. This approach yields the “acoustic free velocity,” corresponding to a volume velocity source that characterizes the original sound source. Subsequently, the source impedance is obtained using the acoustic free velocity in conjunction with the load impedance and acoustic pressure in the acoustic circuit. The method is demonstrated using a compressor driver source attached to an impedance tube. Validation of the measured source strength and source impedance is conducted using a two-load method. Prediction of muffler insertion loss shows good correlation with experimental measurements.