Data from a set of conventional beamformers, each steered to a point in location (and frequency), are analyzed in beam-space processing. By selecting a location sector of interest, and by using only those beamformers which are steered within this sector, processing is in a Reduced-Dimension Beam-Space (RDBS). For spatial-spectrum estimation, advantages of processing in a RDBS rather than in element-space include; reduction in data and therefore computation required for spatial-spectral analysis, reduction in resolution thresholds, and attenuation of out-of-sector sources through spatial filtering. A beam-space preprocessor structure provides the element-space to RDBS transfor-mation. For broad-band source processing, its objectives are data reduction, spatial filtering and broad-band source focusing. In this paper we investigate beam-space preprocessor design.