## 4 Results  
### Analysis of Acoustic Parameters in the Function of Source Rotation  
To describe the differences in measurements, an analysis was conducted on the variations in these parameters as a function of the source rotation, which is one of the methods for analyzing the influence of source directivity on acoustic measurement results. The graphs illustrating these dependencies for the investigated sources are shown in Figures 6-9. In this chapter, the most crucial data were analyzed to illustrate the essential differences across the sources, while Section 4.2 will comprehensively compare the sources with single number parameters. Point 1 was analyzed in two representative frequency bands, while 1000 Hz emphasizes the proper results received with omnidirectional sound sources and 4000 Hz octave band--the significant dispersion in the received results. For the frequency of 1000 Hz (Figures 6 and 7), changes in the value of the C80 parameter are similar regardless of the tested source, and they remain within the border of 1.5 dB, which is the JND for this parameter. The most minor changes in C80 can be observed for the coupled and dodecahedral loudspeakers. For the cubic source, the differences were the most significant. Besides the rotational changes, the obtained C80 values differ significantly in absolute value regarding the sources used. Despite all tested sources being qualified for measurements in this frequency range and exhibiting good omnidirectional quality, the range of results exceeded 4 dB, which requires further analysis and verification as two of the used sources were commercially available, professional sound sources. This is an important finding indicating that the currently used standards for omnidirectional sources qualification may not be accurate as even the professional sound sources (cubic and dodecahedron) provide the dispersion in measured values (such as 2 dB in C80 in 1000 Hz,0.2 s in EDT in 4000 Hz). However, with the detected dispersion in the dodecahedral and cubic source results, the coupled speakers received proper compliance with professional sources. The shape of the curves observed in the T30 analysis may indicate the variability across the measurements. However, it is essential to note that the absolute difference in the T30 values was within 0.08 s across all sources, and the maximum dispersion between the coupled speakers and dodecahedral source was 0.05 s, which is below the JND in this case and qualifies all sources for proper T30 estimation in this frequency range. As T30 is the most important reverberation parameter used for the calibration of geometrical models, proper compliance between the used sources is essential. Regardless of the step rotation, all sources provided the dispersion below the JND. Figure 6: The results of the measurement of EDT and T30 parameters in the 1000 Hz octave band performed with the 3 versions of omnidirectional sound sources in the function of source rotation. Figure 7: The results of the measurement of D50 and C80 parameters in the 1000 Hz octave band performed with the 3 versions of omnidirectional sound sources in the function of source rotation. Analyzing the frequency of 4000 Hz (Figures 8 and 9), significantly worse results can be observed for the coupled loudspeakers, which also corresponds to a significant deterioration in the omnidirectional quality of this source type at high frequencies. In this case, the discrepancies between the sources directly stem from differences in their directivity. It is observed in which case the loudspeakers were facing the microphone or the walls of the room, and the conclusion is that in this frequency range, even if the requirements set by ISO 3382 standards regarding the source directivity were met, the coupled speaker source should not be used in measurements. This is also an essential finding that even when the standard conditions are met and higher averaging is performed, the differences between the omnidirectional sources used for measurements could be significant.