The results of an experimental study of the effects of several slot type casing treatment (STCT) configurations on ducted counter rotating fan model (DCRF) noise are given in present work. The casing treatment design parameters such as lattice duty cycle and the cavity height were varied. It is shown that the most important parameter is the duty factor of the lattice. The configuration of STCT, which provides the greatest reduction of sum sound power level of the fan model was installed over the second rotor only and had the highest duty factor.