The document discusses measurements of octave wave sound signals in a ducted axial fan under stable operating conditions. Experiments were conducted to analyze sound pressure level variations at different rotor speeds between 2400-3600 RPM with the throttle position fixed at 7 cm. Microphones were used to measure sound levels from 11Hz to 11100Hz in decibels. The results showed that sound pressure levels generally increased with rotor speed, ranging from 79-105 dB. Higher pressures and amplitudes correlated with increased sound levels. The experiments provide insight into fan acoustics under stable flow conditions.