# An Acoustic Way to Support Japanese Children's Effective English Learning in School Classrooms
## 3 Results and Discussions  
### Acoustic Measurements  
In the classroom, the measured unoccupied noise level, L\({}_{\text{Aeq,10s}}\), was 31.3 dBA with the air conditioners turned off. Occupied noise level varied around 40 dBA to 50 dBA during English tests with no one speaking inside the room although lessons in other rooms and playground were carried on. The American Speech-Language-Hearing Association recommends to ensure unoccupied classroom noise level \(\leq\)35 dBA [56]. Correspondingly, the Japanese school building guidelines [36] recommend L\({}_{\text{Aeq,T}}\leq\) 40 dBA, where T indicates the measurement period that can be determined depending on the situation. Table 4 shows the estimated RT and STI, calculated by the methods explained in Section 2.4. Likewise, the recommended RT for unoccupied furnished classrooms is 0.6 s at maximum, as average values over octave bands with centre frequencies of 500 Hz, 1 kHz, and 2 kHz (according to the American standard [56,57], for classrooms \(\leq\) 283 m\({}^{3}\)) or similarly for octave bands with centre frequencies of 500 Hz and 1 kHz (according to the Japanese guidelines [36], for classrooms \(\leq\) 200 m\({}^{3}\) approximately). Unlike the common practice of simply measuring the room reverberation and STI, often seen in architectural acoustics, the results we obtained informs us the combined characteristics of the unoccupied furnished room and either of the utilised sound amplification systems. As shown in Table 4, the RT values of both systems are almost within the recommended range with little variation between the two sets although System B is slightly better than System \begin{table}
\begin{tabular}{c c} \hline \hline
**Question Difficulty Level** & **Correct Answer Rate \(p_{\text{c}}\)** \\ \hline Level 4 & \(p_{\text{c}}\leq 40\%\) \\ Level 3 & \(40\%<p_{\text{c}}\leq 60\%\) \\ Level 2 & \(60\%<p_{\text{c}}\leq 80\%\) \\ Level 1 & \(80\%<p_{\text{c}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Question Difficulty. \begin{table}
\begin{tabular}{c c} \hline \hline  & **Explanation of the Explanatory Variable** \\ \hline Difficulty Level (1, 2, 3, 4) & difficulty of word pair in question \\ Test Identifier (1 st, 2 nd) & habituation effects within each lesson \\ Week (1, 2) & habituation effects over two weeks \\ Sound Amplification System (A, B) & acoustic characteristics \\ Seat Group (1, 2, 3, 4, 5) & Seat position defined in Figure 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Explanatory variables assumed in the study. A. The STI, on the other hand, are better with the System B at all measurement positions, compared to that with System A. According to an indication provided in the standard [50], STI > 0.76 observed at all positions with System B imply \"Excellent intelligibility\", but STI > 0.66 observed at all positions except at position (2) with System A imply \"High speech intelligibility\", and STI > 0.62 at position (2) with System A still implies \"Good speech intelligibility\". In comparison with that in RT values, the difference in transfer functions between the two systems was more clearly observed as depicted in Figure 4. The frequency bands between 125 Hz and 8 kHz are understood to contain the most elements of English speech sound [31]. Therefore, signals over this range should be clearly audible (e.g., SNR \(\geq\) +15 dB is recommended in [56]) when English speech stimuli are presented to children in their classrooms. The frequency response of System A reveals that the signals arriving at each listening point diverge more than that of System B. It indicates the difficulty of using System A to ensure that everyone can hear speech sound very well at wherever they are in the same room without harming hearing of no one, including those close to the loudspeakers. System B exhibits its relatively flat response at least over the frequency bands between 200 Hz and 10 kHz at many measurement positions.