Generation of desired signals from acoustic drivers

Abstract A general but systematic procedure has been developed to control transient signal generation for the study of internal noise propagation from aircraft engines. Transform techniques are used in a simple algorithm to produce signals—pulses in this study—of any desired waveform from acoustic drivers. By a judicious input, the accurate driver response function is calculated. From the driver response function the limiting frequency characteristics are determined. The undesirable frequencies where the driver response is poor are eliminated from the analysis. The inverse of the response function is then convolved with the desired signal to produce a synthesized signal. The shape of the synthesized signal is in general quite awkward, in both the time and the frequency domain. Nevertheless, when the distorted signal is fed into the driver, the driver generates the desired signal. The driver is operated in two environments—in a free field and in a duct—and results are presented to show the impedance matching effect of the driver. A set of results with a high frequency cut-off value as a parameter is given to demonstrate the extent of the applicability of the synthesis procedure. The error in the numerical inversion is highlighted. The results show that, within the imposed guidelines, it is possible to generate desired signals through the signal synthesis procedure.