Investigation of Chinese word recognition scores of children in primary school classroom with different speech sound pressure levels

Chinese word recognition (CWR) test was conducted by grades 3 and 5 children under the different conditions of reverberation time (RT), background noise level (BNL) and speech sound pressure level (SSPL) in three primary-school classrooms. The CWR scores and signal to noise ratios (SNRs) have been obtained at listening positions. Results show that the CWR score for grades 3 and 5 children increases with increase of SSPL, decrease of RT or increase of age, but it decreases with increase of BNL under the same conditions. For a mixed noise of 56 dBA (speech-spectrum-like noise and ambient noise), the CWR scores in the classroom for grades 3 and 5 children reach a peak at SNR of 15–20 dBA under the same RT and age of children condition. For the natural ambient noise, the CWR score for grades 3 and 5 children gradually increases with increase of the SNR. The high SSPL could not guarantee good CWR for children in classroom, which also depends on RT and BNL in classroom. When the classroom has long RT or high BNL, the increase of SSPL would not be necessarily to achieve better CWR. The novelty of the present study is to further evaluate and confirm the results under environments of real classrooms (not simulated room in laboratory).     

Improving speech intelligibility in classrooms through the mirror image model

Optimal classroom acoustical design can directly enhance students’ learning efficiency. Effective acoustical designs are important and necessary to achieve a high degree of speech intelligibility for listeners. A speech intelligibility metric, U₅₀, at different receiver positions in a classroom of 10 m × 8 m × 6 m was obtained by numerical simulations based on the mirror image model, with and without the uniform surface absorption coefficient. Comparisons show that increasing the absorption coefficient at the back wall can increase the speech intelligibility metric U₅₀ to the largest extent in the classroom. A numerical case study was then conducted in a typical classroom of 10 m × 10 m × 3.5 m, and the speech intelligibility was assessed through a third-order polynomial of Wonyoung and Murray [Wonyoung Y, Murray H. Auralization study of optimal reverberation times for speech intelligibility for normal and hearing-impaired listeners in classrooms with diffuse sound field. J Acoust Soc Am 2006;120(2):801-7].     

A study on the optimal English speech level for Chinese listeners in classrooms

Speech intelligibility in classrooms affects the learning efficiency of students directly, especially for the students who are using a second language. The speech intelligibility value is determined by many factors such as speech level, signal to noise ratio, and reverberation time in the rooms. This paper investigates the contributions of these factors with subjective tests, especially speech level, which is required for designing the optimal gain for sound amplification systems in classrooms. The test material was generated by mixing the convolution output of the English Coordinate Response Measure corpus and the room impulse responses with the background noise. The subjects are all Chinese students who use English as a second language. It is found that the speech intelligibility increases first and then decreases with the increase of speech level, and the optimal English speech level is about 71 dBA in classrooms for Chinese listeners when the signal to noise ratio and the reverberation time keep constant. Finally, a regression equation is proposed to predict the speech intelligibility based on speech level, signal to noise ratio, and reverberation time.     

Assessing the intelligibility of speech and singing in Mudejar-Gothic churches

Speech intelligibility in these places of worship has been assessed through a study of the spatial distribution of the RASTI and the energy-based acoustic parameters, clarity for speech, C₅₀ and definition, D₅₀. Parameters have been obtained by intensity-modulated stationary noise (IMN) signals and by maximum length sequence (MLS) signals in order to obtain the impulse responses. The 12 churches analysed correspond to the same highly characteristic architectural typology of southern Spain, and measurements were taken without occupancy. A full correlation between those RASTI, C₅₀ and D₅₀ parameters produced by different experimental techniques has been carried out. This correlation has lead to a more profound characterization of these churches from this functional point of view, together with an analysis of the capability of each parameter to take into account the different aspects in the degradation of the signal from speaker to listener in a room, and has also lead to a study of the subjective range of qualification of the energy-based acoustic parameters. Simultaneously, a comparison has been made of the values of those variables with those expected from a semi-empirical model deduced for these religious spaces.     

Psychological experiments on listener envelopment when both the early-to-late sound level and directional late energy ratios are varied, and consideration of calculated LEV in actual halls

The purposes of this paper are to clarify the relation between listener envelopment (LEV) and two physical factors, namely, early-to-late sound level C₈₀ and directional late energy ratios (DLRs), and to demonstrate the significance of evaluating LEV using C₈₀ and DLRs. Firstly, two psychological experiments are performed. In the first experiment, the results show that the previous findings about the effects of late reflections from lateral, overhead, and behind the listener on LEV are valid when they also consist of plural directional energy components, as are found in real sound fields. In the second experiment, the relational equation among LEV, C₈₀, and DLRs is derived from results when the physical factors are simultaneously varied. Secondly, psychological scores for LEV are calculated in actual halls by applying measured values for C₈₀ and DLRs to the equation. The results show that the differences in LEV among different seating positions and in the spatial uniformity of LEV among different halls are expected to be significantly large depending on the values of C₈₀ and DLRs. This suggests the significance of evaluating LEV by means of C₈₀ and DLRs.