The aim of this study was to test the hypothesis of independent processing strategies in adjacent binaural frequency bands underlying current models for binaural speech intelligibility in complex configurations and to investigate the effective binaural auditory bandwidth in broad-band signals. Speech reception thresholds (SRTs) were measured for binaural conditions with frequency-dependent interaural phase differences (IPDs) of speech and noise. SRT predictions with the binaural speech intelligibility model by Beutelmann and Brand (2006, J. Acoust. Soc. Am. 120, 331-342) were compared with the observed data. The IPDs of speech and noise had a sinusoidal shape on a logarithmic frequency scale. The bandwidth between zeros of the IPD function was varied from 18 to 4 octaves. Speech and noise had either the same IPD function (reference condition) or opposite signs of the IPD function (binaural condition). Each condition had two subconditions with alternating and non-alternating signs, respectively, of the IPD function. The binaural unmasking with respect to the reference condition decreased from 6 dB to zero with decreasing IPD bandwidth for the alternating condition while it stayed significantly larger than zero for the non-alternating condition. The observed results were well predicted by the model with an analysis filter bandwidth of 2.3 equivalent rectangular bandwidths (ERBs).