The purpose of this study is to investigate the temporal changes of the Turbulent Kinetic Energy (TKE) of an impinging rectangular self-excited jet in order to identify a reduced zone that is active in producing TKE. An experimental set up consisting of a rectangular jet impinging on a slotted plate was considered for a Reynolds Number Re= 5435. This configuration is accompanied by a high level of noise due to the appearance of self-sustained tones that occur in optimal conditions for energy transfer between fluctuating velocity and acoustic field. High Speed Tomographic Particle Image Velocimetry (PIV) technic was used to evaluate the Turbulent Kinetic Energy (TKE) field derived from the aerodynamic one. Through this study, it was found that a reduced volume of height of 0.5* H and a length of 2* H (where H is the height of the nozzle exit) was satisfactory to represent the three-dimensional TKE activity between the jet exit and the plate. The findings of this research lies in investigating the evolution of the TKE that could feed the acoustic generation in order to develop new techniques of noise control. Such sub-volume of the flow would also save a considerable time of calculation.