Experimental acoustic investigation of under-expanded free and impinging jet is carried out for various nozzle-plate spacing. The reservoir pressure is slowly increased from atmospheric pressure to 6 bar and than decreased from 6 bar to atmospheric pressure. The free jet acoustic radiation remains same for both paths but it is observed that for impinging jet the acoustic radiations differ in some regions. The hysteresis effect observed in acoustic characteristics may be due to the presence of hysteresis effects in the recirculation zone of the impinging jet. This variation is significant for nozzle-plate spacing of 2 to 4 times jet diameter. It is also seen that the acoustic staging occurs for low pressure and high pressure for small and large nozzle-plate spacing, respectively. © 2013 Acoustical Society of America.