Equalization of Nonlinear Propagation Distortion in Cylindrical Waveguides

Abstract

A model-based pre-equalizer for propagation-induced distortion of acoustic waveforms in an air-filled waveguide at high sound pressure levels is developed. The nonlinear distortions introduced by propagation are modeled using Burgers propagation model. This equalizer is stimulus-independent and mitigates nonlinear distortion at some predefined distance in the waveguide. The pre-equalizer digitally propagates the waveform backwards using a sign-inverted propagation model. The output of the pre-equalizer is fed to the waveguide. When the forward model completely characterizes the waveguide, the waveforms arriving at the chosen destination will be identical to a delayed version of the input signal fed to the pre-equalizer. Experimental evaluations employing sinusoidal and multitone stimuli demonstrated approximately a two-fold reduction in the intermodulation distortion and a four-fold reduction in total harmonic distortion at low frequencies. These results represented a two-fold improvement over a model-based method available in the literature.