The standing-wave thermoacoustic prime mover is a device to convert heat into work in the form of sound. It is one of the most potential applications for a thermoacoustic prime mover to utilize low-grade heat source to drive a refrigerator or electrodynamic linear alternator. Low efficiency of the device becomes interesting to be studied; it is because of no optimum heat exchange between the channel wall and the working gas that occur in the stack. The stack is the main part of the thermoacoustic prime mover in where the thermoacoustic energy conversion process takes place. The ωτ parameter is regarded as a nondimensional parameter determining the efficiency of the heat exchange in the stack and it depends on the hydraulic radius of the stack. This experiment was carried out by changing the hydraulic radius of the stack to control the value of ωτ. The stack was made of a pile stainless steel wire mesh because it is easier to vary the hydraulic radius than another kind of stack. The length of the resonator is 1.28m and air at atmospheric pressure is used to fill the resonator as the working gas. Experimental results show that ωτ affecting the onset temperature difference, frequency, pressure amplitude, and acoustic power. Finally, ωτ parameter is a useful property which is needed to be considered to enhance the performance of thermoacoustic prime mover.