# Bone Conduction Auditory Navigation Device for Blind People
## 4 Design of the Warning Sound
### Phase 1  
#### 4.1.1 Experimental Scheme  
A total of nine test sounds, shown in Table 2, were generated and used in the experiment. The subjects were asked to evaluate the randomly reproduced test sounds based on the semantic differential (SD) method. In this experiment, the 27 adjectives shown in Table 3 were adopted to evaluate the warning sounds. To evaluate the extent of each adjective, seven bipolar categories were adopted. The subjects were ten males in their 20s. As described above, the experiment was carried out by simultaneously wearing both the bone-conduction device and headphones. The evaluated warning sounds and environmental sounds were then played through the bone-conduction devices and headphones, respectively. The headphones reproduced environmental sounds recorded by HATS on the campus of the Tokyo University of Science. The recorded environmental sounds were captured in a rather calm situation (\(L_{\text{eq}}\): 56 dB) without any human voices but including some road traffic noise from a distant road. Note that the environmental sound data was reproduced by the headphones at the same level (\(L_{\text{eq}}\): 56 dB) as the that of the on-side environment. The reproduction level of the warning sound from the bone-conduction device was fixed by following the scheme described in the next section.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Phase 1** & Determination of “basic waveform types”: triangle, square, and sawtooth waves \\
**Phase 2** & Determination of “duration of playback and pausing times”: from 0.1 s to 1.6 s \\
**Phase 3** & Determination of “duration of playback and pausing times”: from 0.01 s to 0.1 s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Each of the contents investigated in the three phases.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Condition** & **Wave Type** & **Fundamental Frequency [Hz]** \\ \hline Tri\_400 & & 400 \\ Tri\_800 & Triangle wave & 800 \\ Tri\_1200 & & 1200 \\ \hline Squ\_400 & & 400 \\ Squ\_800 & Square wave & 800 \\ Squ\_1200 & & 1200 \\ \hline Saw\_400 & & 400 \\ Saw\_800 & Sawtooth wave & 800 \\ Saw\_1200 & & 1200 \\ \hline \hline \end{tabular}
\end{table}
Table 2: List of the warning sounds adopted in Phase 1 of the present study.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
1 & Shrill & Profound & 10 & Safe & Danger & 19 & Powerless & Powerful \\ \hline
2 & Uncomfortable & Comfortable & 11 & Relaxed & Busy & 20 & Weak & Strong \\ \hline
3 & Nervous & Easy & 12 & Slow & Rapid & 21 & Calm & Harsh \\ \hline
4 & Unattractive & Attractive & 13 & Not oppressive & Oppressive & 22 & Poor & Rich \\ \hline
5 & Bad & Good & 14 & Casual & Serious & 23 & Dark & Bright \\ \hline
6 & Dull & Funny & 15 & Loose & Tense & 24 & Inconspicuous & Appealing \\ \hline
7 & Not Hearing-friendly & Hearing-friendly & 16 & Mild & Severe & 25 & Dull & Sharp \\ \hline
8 & Gloomy & Sunny & 17 & Quiet & Loud & 26 & Luxury & Cheap \\ \hline
9 & Not Surprising & Surprising & 18 & Moderate & Exciting & 27 & Low & High \\ \hline \hline \end{tabular}
\end{table}
Table 3: List of the 27 pairs of adopted adjectives.