Acoustic measurements of sources in non-ideal acoustic environments, often the case in industrial product development, issue challenges in source characterization. This study investigates the room-acoustical effects of a bespoke fan test facility on aeroacoustic source characterization via a second-order scheme of spherical harmonics of the half-space. An experimental test of a compact monopole-like sound source reveals the influence of the room's transfer function at low frequencies. Applying the scheme to a benchmark case of a low-pressure axial fan at different loading conditions showcases a satisfactory estimation of sound power and directivity.