An analytical approach for predicting the rotational sound due to blade loadings in propeller ducts, based on definable propulsion quantities is presented. It is assumed that the sound field in the propeller plane may be represented by expanding the rotating net blade pressure distribution in a suitable series that satisfies both the wave equation and the boundary conditions associated with the duct and hub. The equations allow for the calculation of the spectral and spatial sound‐pressure distribution along the axis and radius. The validity of the analytical approach is investigated by exploring the sound field of a full‐scale model duct under measured operational conditions. Calculated and measured sound pressures along the duct wall in front and in the propeller plane are in good agreement. Behind the propeller plane, the deviations increase. This effect may result from an increased turbulence behind this plane as demonstrated by a spectral analysis. The analytical approach did not consider a finite tip clearance. Effects of a variable tip clearance on the sound field were explored experimentally. An increase of tip clearance from 0.38 to 1.5 in. resulted in a reduction of the over‐all sound pressure level by 5 dB.