## 4 Discussion
### Elicited Constructs
#### 4.3.1 Perceived Source Loudness and Distance  
The attribute with the highest audibility index was Perceived Source Loudness (PSL). This result was expected, as sound pressure level (SPL) depends on the inverse square law. The perception of source distance is also identified as one of the most salient attributes in Table 5, and it is labelled here as Apparent Source Distance (ASD). While PSL and ASD might initially seem to be obvious attributes to be elicited from different physical source-listener distances, the potential dependencies of their perceived magnitudes on the listener's position and head orientation require systematic investigations, since physical and perceived quantities may not be consistent. [PERSON] and [PERSON] (2013) found that humans tend to overestimate the perceived distance of sound source (i.e., ASD) within about 1 m source-listener distance, but underestimate it beyond that. A similar trend was also observed by [PERSON] et al. (2014). However, the previous research considered sound source and listener positions only in the central axis of the space, with the listener always facing towards the source. Our results indicating PSL and ASD as salient differences perceived across different listener positions and head orientations might be associated with other perceptual cues than just the SPL that depends on the physical source-listener distance. With the head oriented towards 90\({}^{\circ}\) to the left from the on-axis of the source (e.g., P1-90\({}^{\circ}\)), the direct-to-reverberant energy (D/R) ratio, which is widely known as the absolute cue of ASD ([PERSON] et al., 2014), would be higher for the right ear-input signal than for the left ear one. Furthermore, considering the binaural unmasking phenomenon ([PERSON] and [PERSON], 2014), the source masking of reverberation arriving from the back of the concert hall might be weaker at the 90\({}^{\circ}\) orientation compared to 0\({}^{\circ}\), which would also imply that Perceived Reverb Loudness (PRL) would be greater at the contralateral ear than at the ipsilateral ear. This might eventually lead to some differences in the perceived magnitudes of ASD, PSL and PRL as a function of head orientation, even at the same source-listener distance. This hypothesis might also be an explanation for the finding by [PERSON] and [PERSON] (2014) that reverberation received by the contralateral ear plays a more important role than that received by the ipsilateral ear on perceived externalisation in the auralisation of a room over headphones. The perceptual mechanism of ASD, PSL and PRL perceptions depending on listener position and head orientation will be quantitatively investigated in our future study.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Attribute** & **Definition** & **End Labels** \\ \hline Perceived Source Loudness & The point-source loudness perceived at different locations & Quiet-Loud \\ Listener Envelopment & The feeling of being surrounded by the reverberant field & Less-More \\ Apparent Source Width & The perceived impression of width given by the sound source fused with & Narrow-Wide \\ Apparent Reverb Width & The perceived impression of width given by the late reverberant field & Narrow-Wide \\ Apparent Source Distance & The perceived distance between the listener and the sound source & Close-Far \\ Perceived Reverb Loudness & The reverb loudness perceived at different locations & Quiet-Loud \\ Echo Direction & The perceived direction of arrival for echoes & Central-Lateral \\ Reverb Direction & The perceived direction of arrival for reverberation & Central-Lateral \\ Reverb Brightness & The timbral characteristics of reverberation depending on the level of high & Bright-Dull \\  & frequencies & Bright-Dull \\ Echo Brightness & The timbral characteristics of echoes depending on the level of high & Bright-Dull \\  & frequencies & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Salient attributes with their definitions and end-labels.