Speech intelligibility for different spatial configurations of target speech and competing noise source in a horizontal and median plane

• We have confirmed the existence of spatial unmasking that markedly increases speech intelligibility.
• We have proved that the spatial unmasking is bigger for binaural than for monaural conditions.
• It has been shown that when speech source elevation is increased its intelligibility decreases.
• We have proved that Sentence Test is a sort of universal method for speech intelligibility analysis in variety of conditions.

The speech intelligibility for different configurations of a target signal (speech) and masker (babble noise) in a horizontal and a median plane was investigated. The sources were placed at the front, in the back or in the right hand side (at different angular configurations) of a dummy head. The speech signals were presented to listeners via headphones at different signal-to-noise ratios (SNR). Three different types of listening mode (binaural and monaural for the right or left ear) were tested. It was found that the binaural mode gave the lowest, i.e. ‘the best’, speech reception threshold (SRT) values compared to the other modes, except for the cases when both the target and masker were at the same position. With regard to the monaural modes, SRTs were generally worse than those for the binaural mode. The new data gathered for the median plane revealed that a change in elevation of the speech source had a small, but statistically significant, influence on speech intelligibility. It was found that when speech elevation was increased, speech intelligibility decreased.