Definitive experimental knowledge of discrete-frequency noise reduction, which can be obtained in an aircraft turbofan engine through increased axial spacing between the fan rotor and outlet guide vanes, has been lacking. An experimental scale-model research program has been undertaken to fill this void. Using a unique heavy-gas scale-model anechoic test facility, rearward radiated discrete frequency and broad-band noise was investigated for a scale model fan. Data has been obtained for fan tip Mach numbers of 0.7–1.4, and rotor to OGV spacings of 0.13, 0.5, 1.0, and 2.0 rotor chords. Discrete frequency noise reductions up to 17 dB were obtained. At close spacing, discrete frequency reduction was at a rate greater than 6 dB per double spacing. Relative harmonic content was not influenced by spacing and reduction was independent of rotor speed. No significant change in broad-band noise was observed.