The acoustic signals from effervescent sprays were experimentally investigated across a range of injection pressures, flow rates, and gas to liquid ratios by mass (GLR). An unconventional description of spray features under various operational conditions was obtained through the time-frequency-amplitude distributions of spray acoustic by adaptive optimal kernel (AOK). The acoustic energy was calculated through the Hilbert Huang transfer (HI-IT) method and was confirmed to be affected by both the GLR and air flow rate. A new evaluation of spray unsteadiness was established based on this finding. The results show that the gas flowing out of the orifice leads to an increase in the amplitude of the high frequency component. Discrete phenomenon in effervescent sprays was exactly observed by AOK spectrogram as the amplitude distribution was discontinuous with time and the amplitude fluctuations showed variation in different conditions. The factors influencing the acoustic energy include both air and liquid flow rate. The unsteadiness levels under different conditions were calculated after the new spray unsteadiness was evaluated through a simple atomizer. The unsteadiness levels had a low value when the GLR was higher than 5% and varied across a wide range when the GLR was below 4%. The flow regime had a significant effect on the spray unsteadiness as the bubbly and churn flow regimes produce a relatively stable spray, whereas the slug flow regime induces unsteadiness. (C) 2015 Elsevier Ltd. All rights reserved.