## 5 Summary and Discussion
In the second part of this study, the main correlates of the annoyance evaluations of vacuum cleaner noise were obtained in two listening tests. The first listening test included original and modified vacuum cleaner noise samples. The main correlates of the annoyance evaluations were found in this listening experiment. The second listening experiment was divided into four parts, and each part was designed in a full factorial experiment (between loudness and sharpness) with different experimental methods and ranges. The possible interaction between loudness and sharpness was investigated in these experiments. The first listening test showed that the overall loudness, sharpness and especially tonal components at lower and higher frequencies play crucial roles in annoyance perception. The correlations between these three parameters and annoyance were found to be significant. The coefficients for the three correlations were found to be 0.963 for loudness, 0.763 for sharpness, 0.354 for tonality at low frequencies and 0.454 for tonality at high frequencies. However, there is a relatively strong correlation between loudness and sharpness (0.778) and a moderate correlation between loudness and hearing model tonality (0.493). Although there is a strong correlation between loudness and sharpness, which might hint at a degree of multi-collinearity, sharpness was taken into account due to two reasons: Firstly, based on the range of differences with high frequencies, observed in Figure 8, it makes sense to include sharpness as a parameter due to the variation. It is possible to have the same loudness values and different sharpness values. Secondly, the broadband noise-like nature of vacuum cleaner sounds changes its color significantly by changing the high-frequency content. An expert listening to the recordings can directly relate the mentioned characteristics: different vacuum cleaners have different band-noise characteristics with different amounts of high-frequency content. Moreover, changing the high-frequency content of vacuum cleaner noise is achievable by applying sound-absorbing materials at the air exit and other slits, as observable in some of the \"low noise\" vacuum cleaners on the market. Eventually, variation in the sharpness can be achieved by means of noise reduction techniques, as mentioned in different pieces of literature referred to in this study. In the first three parts of the second experiment (Part 1, Part 2 and Part 3), a \(3\times 3\) factorial design was used in different experimental methods, and the significance of the loudness-sharpness interaction was tested using a repeated measures ANOVA. In the last part, the loudness range was extended in the \(5\times 3\) factorial design experiments so that the investigated range of loudness was close to the range observed from market research and the interaction could be investigated in louder and quieter stimuli. For all four parts, no significant interaction between loudness and sharpness was found. In Parts 1, 2 and 3, three different experimental methods were compared with each other using the same stimuli, same subjects and same playback conditions. The investigated methods were slider scale (Part 1), magnitude estimation (Part 2) and random access (Part 3). As expected, the slider scale and random access methods showed quite high similarity, whereas the magnitude estimation method showed clear distinctions for loudness level changes, although statistical significance was not observed when the entire database was considered. This different behavior from the magnitude estimation test can be the reason for the logarithmic bias [41] since the stimulus with the lowest loudness and sharpness values was used as the anchor stimulus. In future studies, this effect could be further investigated using another anchor stimulus, such as the other extreme of the stimulus pool (the loudest and sharpest stimulus) or a stimulus right in the middle.