Thermoacoustic engines (TAEs) are devices that convert thermal energy input to sound energy output which can be used to drive different mechanisms. TAEs are a promising technology since they are environmentally friendly and require low maintenance and costs. The main component of the TAE device is the stack which is a solid porous material that allows heat transfer between the fluid and stack plates. Thermoacoustic engines take heat from a hot reservoir and converts some of the heat energy inside the stack to sound energy while dumping the excess to the heat sink. The purpose of this paper is to investigate the stack length and position using the experimental apparatus as well as the numerical modelling. Experimentations are conducted alongside the numerical analysis. The numerical model is governed by the non-isothermal conjugated heat flow of the unsteady Navier-stokes equations. Pressure and velocity are monitored at different locations along the resonator. Experiments conducted showed that the stack position and length have an influence on the efficiency of the TAE. For both lengths tested, the efficiency increased as the center position of the stack moved further away from the pressure anti-node, however this was not observed in the numerical analysis, as the maximum output was obtained with stack placed at 0.3L from the closed end of the tube. Moreover, the longer stack of 9cm gave a better performance than the shorter stack of 4.5cm.