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The cooling fans for small air cooled engines can be an important contributor to overall noise levels. Frequently, the noise spectrums contain strong pure tone components which degrade sound quality. For fifteen years, Briggs & Stratton has been spacing the fan blades unevenly to reduce the pure tone noise caused by equally spaced fan blades. This phase modulation technique has been very successful, however the modulated fin spacing produces an inherently unbalanced part and it is desirable to minimize the amount of modulation required. Unfortunately, building experimental fans with varying amounts of modulation is expensive and time consuming. This paper describes a system for electronically simulating fan noise to be used for subjective testing. A multifunction synthesizer was used to generate signals with varying amounts of phase modulation. The modulated signals were mixed with filtered pink noise to closely approximate the total fan noise.