## 5 Experiment 2
### Results  
In total, 350 annoyance ratings were collected (25 subjects \(\times\) 14 stimuli), each of which was assigned to a particular subject and a specific stimulus (of the total 21 stimuli). The results of experiment 2 are illustrated in Figure 7.  
A simple linear mixed effects model such as in Equation (1) was not found to be sufficient to predict annoyance observed in experiment 2. However, a similar linear mixed effects model as in Equation (2) was found to be optimal to predict annoyance in this experiment:  
\[y_{ik}=\mu+\tau_{\text{B},i}+\beta\cdot L_{\text{AE},\text{F}}+\gamma\cdot L_{ \text{Aeq},\text{B}}+\theta\cdot S_{ik}+\gamma_{\text{B},i}\cdot L_{\text{Aeq},\text{B}}+u_{k}+\epsilon_{ik}. \tag{3}\]  
Model parameters in Equation (3) are the same as for Equation (2). The significance levels were comparable to those for experiment 1. Model coefficients are shown in Table 4. Annoyance increased slightly, however significantly, with the playback number. Figure 7: Results of experiment 2: mean acoustic comfort ratings across subjects (and their 95% confidence intervals) are shown as a function of \(L_{\text{AE},\text{F}}\) (**above**) or for different background types (**middle**) and \(L_{\text{Aeq},\text{B}}\) (**below**). Similar to the results of experiment 1, also for the data collected in experiment 2, the main predictor of annoyance was \(L_{\text{AE,F}}\) (\(p<0.001\)). Annoyance increased with increasing \(L_{\text{AE,F}}\). Background type was a significant predictor of annoyance (\(p<0.05\)). Whereas no difference was found between average annoyance ratings for stimuli without background sounds and those with eventful background sounds, stimuli containing less eventful background sounds were found to be less annoying on average than the other two categories. Furthermore, annoyance increased slightly, however significantly, with the playback number (\(p<0.001\)), as was the case for experiment 1. The main effect of the background level (\(L_{\text{Aeq,B}}\)) on annoyance was not significant (\(p>0.05\)). The interaction between background type and background level (\(L_{\text{Aeq,B}}\)) can be observed in Figure 8. This interaction missed the significance level by a small margin (\(p=0.05\)). With increasing \(L_{\text{Aeq,B}}\), annoyance from stimuli with eventful background sounds did not change significantly and was on average at the level of annoyance from stimuli without mixed background sounds. Annoyance from the stimuli with less eventful background sounds decreased with increasing \(L_{\text{Aeq,B}}\), however only from 38 to 46 dB(A). At an \(L_{\text{Aeq,B}}\) of 54 dB(A), annoyance from the stimuli with the less eventful background sound were similar to those for the stimuli with the eventful background sound. That is, when the level of the background sound was sufficiently high, it did not matter which type of background sound was used; at this background sound pressure level, annoyance was not different on average from that for the stimuli without background sound. \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Parameter** & **Symbol** & **Coeff.** & **95\% CI** & \(p\)** \\ \hline Intercept & \(\mu\) & \(-21.989\) & [\(-24.712\);\(-19.266\)] & 0.00 \\ Background type & \(\tau_{\text{B,i}}=\text{No}\) & \(1.298\) & [\(0.019\);\(2.578\)] & 0.05 \\  & \(\tau_{\text{B,i}}=\text{L}\) & \(0\)\({}^{a}\) & \\  & \(\tau_{\text{B,j}}=\text{E}\) & \(2.215\) & [\(0.191\);\(4.238\)] & 0.03 \\ \(L_{\text{AE,F}}\) & \(\beta\) & 0.360 & [\(0.328\);\(0.392\)] & 0.00 \\ \(L_{\text{Aeq,B}}\) & \(\gamma\) & 0.028 & [\(-0.002\);\(0.059\)] & 0.07 \\ Playback no. & \(\theta\) & 0.060 & [\(0.028\);\(0.092\)] & 0.00 \\ Type\(\times L_{\text{Aeq,B}}\) & \(\gamma_{\text{B,i}}=\text{No}\) & \(0\)\({}^{a}\) & \\  & \(\gamma_{\text{B,i}}=\text{L}\) & \(0\)\({}^{a}\) & \\  & \(\gamma_{\text{B,i}}=\text{E}\) & \(-0.043\) & [\(-0.086\);\(0.001\)] & 0.05 \\ \hline \hline \end{tabular} \({}^{a}\) Redundant coefficients are set to zero.  
\end{table} 
Table 4: Experiment 2: model coefficients (Coeff.