An approach to spatial-spectrum estimation of broadband sources is described. The approach, termed broadband signal-subspace spatial spectrum (BASS-ALE) estimation, is based on the eigenstructure of a broadband spatial/temporal covariance matrix and is justified by identifying the low-rank character of spatial/temporal observations of broadband sources. BASS-ALE estimators are described which incorporate: source focusing, spatial/temporal noise decorrelating, a signal (or noise-only) subspace generated from the eigenstructure of the transformed spatial/temporal covariance matrix, and broadband source models. Through discussion and simulation, BASS-ALE estimators are compared to the coherent signal-subspace processor (a similar subspace method), and relative advantages of the two are identified. >