Active Noise Control (ANC) systems have proven to be a great alternative to diminish low-frequency noise signals in a large group of applications, considering that an important number of noise sources such as rotatory machines are related with periodical noise signals, Narrowband ANC systems are proposed to overcome this kind of drawbacks. Multi-frequency ANC systems, which are based in an array of Adaptive Notch Filters, are one of the most important architectures aforementioned. The present research evaluates the alternative of use of an optimal step size as part of the Filtered-X Least Mean Square (FxLMS) Algorithm for the Multi-frequency ANC system, developed through the implementation of the Delayed FxLMS algrithm in each adaptive notch filter. Optimal step size value is obtained starting from the operation interval and optimal values of step-size from each single-frequency ANC system.