# Experimental Investigation of Task Performance and Human Vigilance in Different Noise Environments
## 2 Materials and Methods
### Experimental Set-Up  
Figure 2 shows the experimental set-up of noise play and measurement. A sound level meter (AWA5636, Aihua Instruments Co., Hangzhou, China) was placed near the left ear of the subject to perform real-time measurement of the sound pressure level. The sound level meter was calibrated once a day by the sound calibrator (HS6020), with a measurement range of 40-130 dB(A) and a measurement accuracy of \(\pm\)1.0 dB(A). The system consisted of a sound pressure sensor (INV9206, COINV, Beijing, China), USB collection instrument (INV3018 CT, COINV, Beijing, China), and sound measurement software (DASP-V10, COINV, COINV, Beijing, China).  
This study focused on both sound pressure level and noise sharpness. An equivalent A-weighted sound pressure level (L\({}_{\text{Aeq}}\)) in dB(A) is typically used to represent the energy-averaged sound level over some time as measured by a sound pressure level meter. Noise sharpness (acum) is used to measure the high-frequency content of sound, which can reflect the subjective feeling of individuals on the roughness of sound [26]. The sharpness of the sound signal is closely related to the proportion of high-frequency components. The higher the proportion of high-frequency components, the higher the sharpness, and the stronger the subjective feeling of roughness. During the experiment, the outliers of all segments were eliminated with three times the standard deviation, and the mean value and standard deviation were further calculated to obtain the original sound quality parameter (N85-S1). [PERSON] et al. [27] set the allowable safe noise level in the submarine cabin to be less than 80 dB(A) during navigation. Therefore, the second noise exposure condition was N80-S1. Next, the noise sound pressure level was further reduced to 75 dB(A) and the noise sharpness was increased to obtain the third noise exposure condition of N75-S2. The objective noise parameters of the three exposure conditions are shown in Table 3.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Environmental Parameters** & **N85-S1** & **N80-S1** & **N75-S2** \\ \hline L\({}_{\text{Aeq}}\) (dB(A)) & 84.2 \(\pm\) 0.8 & 78.3 \(\pm\) 0.7 & 75.0 \(\pm\) 0.8 \\ Noise sharpness (acum) & 1.28 \(\pm\) 0.03 & 1.30 \(\pm\) 0.03 & 2.42 \(\pm\) 0.04 \\ Air temperature (\({}^{\circ}\)C) & 20.9 \(\pm\) 0.6 & 21.0 \(\pm\) 0.6 & 21.1 \(\pm\) 0.6 \\ Relative humidity (\%) & 26.5 \(\pm\) 8.1 & 29.0 \(\pm\) 7.5 & 24.7 \(\pm\) 5.6 \\ Air velocity (m/s) & 0.12 \(\pm\) 0.01 & 0.13 \(\pm\) 0.01 & 0.12 \(\pm\) 0.01 \\ Black globe temperature (\({}^{\circ}\)C) & 21.1 \(\pm\) 0.6 & 21.2 \(\pm\) 0.6 & 21.3 \(\pm\) 0.5 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Measured environmental parameters under different experimental conditions.  
Figure 2: Schematic diagram of the experimental set-up.  
A comprehensive indoor environment quality tester (MI6401, METREL, Eckental, Germany) was used to measure indoor thermal environment parameters (Table 3). It was assumed that the metabolic rate of the human body was 90 W/m\({}^{2}\)[28] and the thermal resistance of clothing was 0.9 [29]. The predicted mean vote (PMV) during the experiment was estimated to be between \(-0.117\) and 0.375, which indicated that the subjects performed tasks in a thermally neutral state.