## 4 Discussion  
In line with the literature [29; 30], previous research findings showed that [23; 24]_Aesthetics_ and _Loudness_ represent the two main dimensions describing the perception of HVAC noise inside car cabins. In this research, the three most representative adjective couples describing each dimension were considered. For the Aesthetic dimension, the listening test results for the adjective couples of High Quality-Low Quality, Not Annoying-Annoying, and Unpleasant-Pleasant highlighted that the most relevant difference between the two Subject Groups occurred for _High Quality-Low Quality_. More specifically, the Japanese considered the quality of sounds to be significantly lower than Italians in both ICEVs and HEVs and whether the AC was turned on or off, but only at the highest air flow rates. The _Not Annoying-Annoying_ item was found to be affected mainly by the airflow rates and the engine type, with ICEVs considered more annoying than HEVs, especially at low AFRs. Moreover, both the airflow rate and the type of engine showed interaction effects with the subject group in the Ventilation condition, with Japanese considering ICEVs more annoying. This interaction effect disappeared when the air conditioning was turned on. Furthermore, the results for _\"Unpleasant-Pleasant\"_ also showed the main effects of the air flow rates and the engine type in influencing the evaluations. The higher the air flow rate, the more unpleasant the judgements. Both groups considered HEVs more pleasant. For the Loudness dimension, _Loud-Soft_, _Noisy-Quiet_, and _Powerful-Weak_ adjective couples were considered. For _Loud-Soft_, the air flow rates and type of engine affected the evaluations, whether with or without air conditioning on. In general, HEVs were considered softer then ICEVs but both were evaluated as loud as air flow rate increased. Regarding _Noisy-Quiet_, similar to the previous adjective couples, HEVs were considered quieter then ICEVs and both were evaluated as noisy as the air flow rate increased. Finally, considering the _Powerful-Weak_ adjective couple, results showed the main effects of air flow rates and engine type in influencing the evaluations, with ICEVs considered significantly more powerful than HEVs by Japanese, especially at high air flow rates. Although the Air Flow Rates of 75% and 100% were responsible for the general worsening in the Aesthetic and Loudness items for both groups, thus minimizing the \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Powerful-Weak**} & \multicolumn{6}{c}{**Ventilation**} & \multicolumn{6}{c}{**Air Conditioning**} \\ \hline
**Within Subj. Effects** & **SS** & **df** & **MS** & **F** & \(p\) & \(\mathbf{n^{2}_{P}}\) & **SS** & **df** & **MS** & **F** & \(p\) & \(\mathbf{n^{2}_{P}}\) \\ \hline AFR & 502.59 & 3 & 167.53 & 337.29 & \textless{}0.001 & 0.899 & 458.49 & 3 & 152.83 & 233.30 & \textless{}0.001 & 0.860 \\ AFR \(\times\) Subj. Group & 3.56 & 3 & 1.19 & 2.39 & 0.072 & 0.059 & 1.14 & 3 & 0.38 & 0.58 & 0.631 & 0.015 \\ Residual & 56.62 & 114 & 0.50 & & & & 74.68 & 114 & 0.66 & & & \\ Eng. Type & 56.67 & 1 & 56.67 & 151.50 & \textless{}0.001 & 0.799 & 45.50 & 1 & 45.50 & 64.52 & 0.001 & 0.629 \\ Eng. Type \(\times\) Subj. & 0.17 & 1 & 0.17 & 0.45 & 0.507 & 0.012 & 0.01 & 1 & 0.01 & 0.01 & 0.930 & 0.000 \\ Group & Residual & 14.22 & 38 & 0.37 & & & & 26.80 & 38 & 0.71 & & & \\ AFR \(\times\) Eng. Type & 10.29 & 3 & 3.43 & 8.60 & \textless{}0.001 & 0.185 & 8.27 & 3 & 2.76 & 8.98 & 0.001 & 0.191 \\ AFR \(\times\) Eng. Type \(\times\) & 4.42 & 3 & 1.48 & 3.70 & 0.014 & 0.089 & 2.29 & 3 & 0.76 & 2.48 & 0.065 & 0.061 \\ Subj. Group & 45.45 & 114 & 0.40 & & & & 35.02 & 114 & 0.31 & & & \\ Residual & 58 & df & MS & F & \(p\) & \(\mathbf{n^{2}_{P}}\) & SS & Df & MS & F & \(p\) & \(\mathbf{n^{2}_{P}}\) \\ \hline Subj. Group & 4.20 & 1 & 4.20 & 3.40 & 0.073 & 0.082 & 2.69 & 1 & 2.69 & 2.73 & 0.107 & 0.067 \\ Residual & 46.91 & 38 & 1.23 & & & & 37.45 & 38 & 0.98 & & & \\ \hline \hline \end{tabular}
\end{table}