## 3 Results  
The information of time of tool use for each woodworker is given in Table 1. Circular saw appeared to be the major tool to use for woodwork, and nail gun and air compressor were used by all workers. Time of tool use for these five cases was approximately 15-27% in proportion, and the remaining time was full of tasks of gluing, measuring, and material preparing. Unlike other tools that gave continuous noises, the nail gun generated a train of impulsive noises, which made the measurement of cumulative time of use difficult. For example, 18 min were roughly estimated for Subject 3, who actually used a nail gun all afternoon. Frequency spectra of individual tools were measured for simulation modeling (Table 2). Generally speaking, the peaks of noises generated by handheld tools occurred between 1 and 4 kHz, except that generated by nail gun, peaking at higher frequencies (i.e., 4, 8 kHz). Large-size machines generated relatively low levels of noises with the peaks at 500 Hz, except the circular saw that had the peak at 8 kHz. LA\({}_{\text{eqS}}\) derived from personal measuring and simulation modeling, where median values of distances (i.e., 50 cm for handheld tools, 165 cm for large-size machines) were used in Equation (1) for conversion, are shown in Figure 2. It appeared that all five woodworkers were exposed to noise levels peaking between 1 and 4 kHz, and LA\({}_{\text{eqS}}\) were around 80 dBA with that for the right ear being slightly higher than the other (0.2-0.4 dBA). Although the simulated LA\({}_{\text{eqS}}\) fairly matched that from the personal measuring, there were certain differences between both, with an underestimated value for Subject 1 and overestimated ones for the others. The estimated levels at 4 and 8 kHz for Subjects 3 and 4 were apparently higher than that of on-site measurements, suggesting that the biases could be caused by tools that generated high noise levels at those frequencies. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Power Tool**} & \multicolumn{6}{c}{**Time of Use (Min)**} \\ \cline{2-7}  & **Subject 1** & **Subject 2** & **Subject 3** & **Subject 4** & **Subject 5** \\ \hline Circular saw & 20.00 & 58.00 & 48.00 & 57.00 & 44.25 \\ Curve saw & 4.00 & - & - & - & - \\ Orbit sander & - & 2.00 & 4.00 & 8.00 & 3.50 \\ Router trimmer & - & 7.00 & 14.00 & - & 9.50 \\ Drill machine & - & - & 11.25 & 25.50 & 10.00 \\ Pillar drill machine & - & - & - & 6.00 & 1.50 \\ Nail gun & 3.00 & 12.75 & 18.00 & 13.50 & 1.25 \\ Air compressor & 3.00 & 21.00 & 6.00 & 6.00 & 14.50 \\ No use (background) & 182 & 343 & 370 & 316 & 405 \\ \hline
**Total worktime** & 212 & 443.75 & 471.25 & 432 & 489.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Information of time of tool use for woodworkers. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{6}{c}{**Handheld Tool (dB) \({}^{\text{a}}\)**} & \multicolumn{6}{c}{**Large-size Machine (dB) \({}^{\text{b}}\)**} \\ \hline
**Frequency** & **Curve** & **Orbit** & **Router** & **Drill** & **Nail** & **Circular** & **Pillar Drill** & **Air** \\
**(Hz)** & **Saw** & **Sander** & **Trimmer** & **Machine** & **Gun** & **Saw** & **Machine** & **Compressor** \\ \hline
31.5 & 55.3 & 51.7 & 28.0 & 41.2 & 41.7 & 34.3 & 54.1 & 36.8 \\
63 & 71.2 & 67.7 & 46.7 & 66.3 & 53.6 & 64.9 & 60.9 & 57.0 \\
125 & 69.2 & 85.8 & 51.7 & 70.7 & 61.1 & 63.5 & 69.5 & 61.3 \\
250 & 77.3 & 81.4 & 61.9 & 73.3 & 75.4 & 70.1 & 75.8 & 70.3 \\
500 & 84.2 & 78.1 & 77.2 & 86.0 & 84.1 & 74.6 & 88.1 & 78.7 \\
1k & 88.4 & 91.8 & 90.9 & 88.1 & 96.1 & 74.2 & 88.0 & 71.1 \\
2k & 90.7 & 86.7 & 89.5 & 89.8 & 94.1 & 75.8 & 83.6 & 69.2 \\
4k & 87.0 & 87.6 & 87.1 & 89.7 & 97.7 & 84.2 & 82.4 & 69.4 \\
8k & 82.8 & 87.1 & 81.4 & 82.8 & 98.5 & 88.0 & 75.6 & 63.4 \\ \hline \hline \end{tabular} \({}^{\text{a}}\) Measured from a distance of 15 cm; \({}^{\text{b}}\) measured from 100 cm away.  
\end{table} 
Table 2: Frequency spectra (1/1 octave) measured from power tools in operation.