Sound source characteristics may be one of the main causes of objective speech intelligibility metric inaccuracy. In this study, the influences of the sound source directivity and frequency response were investigated using three typical sound sources: an artificial mouth, a monitor speaker, and a dodecahedral sound source. The results show that, the simultaneous influences of directivity and frequency response on the objective speech intelligibility metric are significant, typically with a variation of 0.147 in speech transmission index (STI); sound source directivity may also result in a noticeable difference in the objective speech intelligibility metric, typically with a variation of 0.123 in STI. In comparison with sound sources with a high directivity index (DI), the measurement results for sound sources with a relatively low DI may be higher when background noise is high, and may be lower when background noise is low. The influence of sound source directivity may also depend on the room acoustic conditions, and at receiver position where reflections are abundant, the influence of sound source directivity may be more significant. Not applying frequency response equalisation resulted in large errors in the values being measured, which deviate from the real values of STI by up to 0.172, depending on the original frequency response characteristics of the sound sources that are used.

Acoustic barriers designed for sound insulation block airflow transport at the same time. However, in acoustic engineering, particular scenarios are calling for noise control in a flowing-fluid-filled circumstance. Acoustic metasurfaces, owing to their unique functional characteristics and vanishing size, hold out new solutions for acoustic ventilation barriers. In this review, we trace the development of acoustic ventilation barriers and categorize them into several variants. We focus on the core underpinned physics, such as local resonance and Fano-like interference, that can fulfill the task of simultaneous ventilation and sound-proofing. Since these mechanisms naturally support a very narrow working range, we further underline those efforts taken on expanding the sound-proofing range. Finally, current challenges as well as the outlook of future directions in this emerging field are discussed.

Summary:The subjective Chinese (Mandarin) articulation scores of a total of 50 sound conditions, namely at 12 receiver positions in four rooms, were obtained by expert listeners based on in-situ measured binaural room impulse responses (BRIRs) and binaural technology for headphone reproduction from a phonetically balanced test. The relationship between Chinese speech articulation scores and the speech transmission index (STI) according to IEC 60268-16 was established. The spectrum difference between the average spectrum of Chinese and that recommended by IEC may noticeably influence the measurement results with a STI difference of up to 0.054. However, the STI method can evaluate Chinese intelligibility without modulating the correction factor values recommended by IEC; the standard deviation between the articulation scores and the curve was 5.70%, which is relatively small.2014 Acta Acustica united with Acustica Date

The rate of sound decay in an enclosed space has been used as the measure for assessing the reverbrance initiated by Sabine a century ago. Such evaluation is based on the energy consideration and can be tested by a monophonic receiving system. But, it is questionable for reverberance evaluation of unroofed spaces, such as, traditional Chinese courtyard theatres or Greek/Roman amphitheatres. It can be seen that even the decay rates of the enclosed and unroofed spaces are similar, but their reflectograms show significant difference due to the absence of reflections from top in the unroofed space. The spatial distributions of the reflections toward the listeners for both spaces are also very different. Series of subjective comparison tests of synthetic room impulse responses through stereo-system (pickup and playback) in our laboratory also showed that the reverberance in an unroofed space was quite different from the result through mono-system as in the conventional way following ISO 3382. However, subjective tests through mono-system for enclosed and unroofed spaces with similar decay rate do not show significant difference of reverbrance. Therefore, in an unroofed theatre, the factor of spatial information of the reflections should not be neglected for reverbrance criteria.