The decrease in reactance of perforated plates at high sound pressure amplitudes is of interest for the design of Helmholtz resonator liners. It is associated with the loss of end correction due to flow separation at the orifices. In practical applications, complex acoustic signals impinge on perforations. The loss of end correction due to multiple stimuli of unrelated frequency and phase has not been considered yet. This study assesses and presents an empirical approximation for the reduction of end correction of perforated plates at primary frequencies when flow separation is induced by an additional secondary unrelated high amplitude stimulus.