## 3 Results and Discussion
### Listening  
In the listening part of the experiment, 35 listeners have experienced all 24 experimental conditions defined by the levels of the three investigated factors. Each subject gave 24 responses in total, i.e., one per condition. A total of 840 observations was collected in the form of the A-weighted level of reproduced speech as the dependent variable. As described earlier, the independent variables/factors whose influence was tested were the following:  
* sound reproduction system: two levels (loudspeakers or headphones);
* visual stimulus--dummy head representing the speaker/interlocutor: three levels (none present, dummy head at personal distance, dummy head at social distance);
* speaker voice: four levels (two male and two female). To match the experimental design, a three-way repeated measures ANOVA with all three within factors was implemented to statistically analyze the obtained data. The data in all the groups satisfied the condition of normality, as examined with the Shapiro-Wilk test and the corresponding QQ plots. No outliers have been found. [PERSON]'s test of sphericity was performed, and the Greenhouse-Geisser corrections were applied where required. The resulting ANOVA table obtained from R is shown below as Table 3, with effect size expressed as eta-squared \(\eta^{2}\). Estimated power was added to the table as well. The results of the ANOVA analysis indicate that there is a statistically significant effect of the used sound reproduction system and speaker voice as the main effects on the set A-weighted level of reproduced speech. The interaction of all three factors also shows as statistically significant. However, the calculated effect size in terms of eta-squared (0.01 = small; 0.06 = medium; 0.14 = large) reveals that the only meaningful effect is the sound reproduction system used. Moreover, the power analysis shows that the power of the test (0.7 = adequate; 0.8 = good; 0.9 = strong) is adequate enough to detect the influence \begin{table}
\begin{tabular}{c} \hline \hline
**Visual Stimulus** \\ \hline None \\ Close: dummy head at 85 cm \\ Far: dummy head at 280 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The levels of the visual stimulus (none present, dummy head close to the reader, dummy head far from the reader) as the only factor investigated in the reading part of the experiment, yielding three different experimental conditions the subjects experienced during reading. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Effect/Interaction** & \(d\)**Fn** & \(d\)**Fd** & **F** & \(p\) & \(\eta^{2}\) & **Power** \\ \hline Sound & & & & & & \\ reproduction & 1.00 & 34.00 & 69.556 & \textless{}0.001 * & 0.117 & 1.000 \\ system & & & & & & \\ Visual stimulus & 1.55 & 52.76 & 2.616 & 0.095 & 0.008 & 0.646 \\ Speaker voice & 3.00 & 102.00 & 36.646 & \textless{}0.001 * & 0.010 & 0.770 \\ System/visual & 1.53 & 52.14 & 1.596 & 0.215 & \textless{}0.001 & 0.045 \\ System/voice & 3.00 & 102.00 & 1.623 & 0.189 & \textless{}0.001 & 0.008 \\ Visual/voice & 4.34 & 147.42 & 2.063 & 0.083 & \textless{}0.001 & 0.011 \\ System/visual/voice & 6.00 & 204.00 & 2.153 & 0.049 * & \textless{}0.001 & 0.010 \\ \hline \hline \end{tabular}  
* statistically significant at the 0.05 significance level.  
\end{table} 
Table 3: The three-way ANOVA output table with effect size reported with \(\eta^{2}\) and the results of the power analysis added to the rightmost column. of the main effects, but not to detect the effect of their interactions. In terms of practical significance of the observed differences and the obtained effect size, the only meaningful and truly significant result is the systemic 5 dB difference in the set A-weighted level of speech when listened to over loudspeakers vs. headphones. Table 4 shows that the marginal mean of all A-weighted levels of speech obtained for headphones is 55.0 dBA, and the same quantity obtained for loudspeakers is 49.9 dBA. Respective standard deviations are shown as well.