## 4 Results
### Analysis of the Source Rotation on the Change of the Measured Acoustic Parameters in the Room  
After analyzing the parameter variations as a function of rotation for each source, a comprehensive analysis of all parameters determined at each measurement point was also conducted. The SD/JND analysis was applied following the methodology in [1]. Standard deviations divided by the Just Noticeable Difference (JND) were also calculated to compare parameters expressed in different units (Figures 10-12). JND represents a minor perceptible difference in values of individual acoustic parameters as perceived by humans, and its values were defined in ISO 3382-1 standard. The value SD/JND over 1 indicates the high audibility of the changes in source rotation and should be avoided.  
Figure 10: SD/JND values for dodecahedral source.  
Comparing the graphs, it was observed that the coupled loudspeakers achieve the lowest values of the SD/JND parameter in the frequency range of 500-2000 Hz. However, its performance differs for the parameters selected for the comparison. Above this range, the deviation values significantly increase along with the deteriorating directivity  
Figure 11: SD/JND values for cubic source.  
Figure 12: SD/JND values for coupled speakers.  
characteristics. Based on this, it can be concluded that within this frequency range, the coupled loudspeaker source meets the requirements for indoor acoustic testing devices and achieves better results than analogous commercial systems. For easier comparative analysis, the SD/JND values are also presented in Table 1, where the lowest (green) and highest (red) values are compared for each parameter and each frequency band analyzed.  
Detailed analysis of Table 1 leads to the following conclusions:  
* The coupled speaker solution is unsuitable for measurements in the 4000 Hz octave band as the received values of SD/JND were very high.
* In the overall comparison, the cubic source occurred as the worst across the measured parameters, while in the frequency range of 250-2000 Hz, the coupled speakers performed better or no worse than the dodecahedral sound source.
* EDT--The coupled speakers were selected the best in the range of 250-2000 Hz, proving the superiority over both dodecahedral and cubic sources, while only in the 1000 Hz band did the dodecahedral sources provide the same results as coupled speakers.
* D50--In the frequency range of 500-2000 Hz, all sources performed correctly in those measurements but received decent results as the SD/JND values were significant except for the 250 Hz band.
* C80--The results in measurements with coupled speakers and dodecahedral sound sources were very similar in this parameter except for the octave band 4000 Hz, while the overall values of SD/JND were also relatively small. The worst results were received for a cubic type of source.
* T30--The SD/JND values across all sources and frequency ranges used in the comparison were similar, where no source superiority was proved. This indicates the conclusion that if the analysis will be limited only to reverberation time, the sources perform similarly.  
It is essential to state that the conclusions provided above are based only on the step-rotation source of dispersions (SD/JND analysis), while the differences in the general absolute value between the sources were significant. However, in the current state of research and the state of the art, it is impossible to compare the direct results and state which value of the analyzed parameter was the ground truth.