# On the Sequence of Unmasked Reflections in Shoebox Concert Halls
## 4 Skeletal Reflections Analysis
### Analysis  
The Skeletal Analysis is presented in the form of an echogram. The vertical lines indicate the arrival of an SR, which is the height of the line related to the relative level to the theoretical unobstructed direct sound. The numbers above each vertical line represent the location where the reflection happens, indicated in a short section adjacent to the echogram. Two perception thresholds are shown in the SR echogram in Figure 3 (dashed line), absolute threshold of perceptibility after Schubert (solid line), probable threshold for  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Concert Hall** & **Code** & **Capacity (N)** & **Volume (V)** & **V/N [m3/seat]** & **RT500-1000,occ [s]** & **Floor Rake at Stalls** \\ \hline Große & & & & & & \\ Musikvereinssaal & GMV & 1680 & 15,000 & 8.9 & 2.0 & 0\({}^{\circ}\) \\ Perth Concert Hall & PCH & 1729 & 15,650 & 9.0 & 2.1 & 10–11\({}^{\circ}\) \\ Stavanger & & & & & & \\ Konserthuset [25] & SK & 1500 & 22,168 & 14.8 & 2.2 & 5–6\({}^{\circ}\)[26] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Data for selected concert halls.  
Figure 2: (**a**) Grosß Musikvereinssaal (photo: [PERSON]); (**b**) Perth Concert Hall (photo: Marshall Day Acoustics); (**c**) Stavanger Konserthuset (photo: [[https://sso.no/en/seating-plan-fartein-valen/](https://sso.no/en/seating-plan-fartein-valen/)]([https://sso.no/en/seating-plan-fartein-valen/](https://sso.no/en/seating-plan-fartein-valen/)) accessed on 24 August 2021); (**d**) Comparison of concert hall’s cross-section: (**Black**) Grosß Musikvereinssaal, (**Red**) Perth Concert Hall, (**Blue**) Stavanger Konserthuset [25].  
useful contribution. The absolute arrival time and the Initial Time Delay Gap (ITDG) are shown in the horizontal axis of the echogram.  
The reader should note that reflections from the stage enclosure fill the time gap between the direct sound and the first lateral but are not shown in this analysis. The stage enclosure reflections, due to their direction and the arrival time, are generally masked by the direct sound but contribute to filling in the gap between the direct sound and the first halls reflection.  
When analysing the SRs in Figure 3, the reader should note that as discussed above, the perception thresholds for lateral reflections are lower than from any other direction. Therefore, in reality, if two reflections arrive simultaneously from two different directions, it is likely that the more lateral (perpendicular to the ear) reflection will predominate and  
Figure 3: Skeletal Reflections Analysis for three concert halls: (**a**) Grosße Musikvereinssaal, (**b**) Perth Concert Hall, (**c**) Stavanger Konserthuset. Time indicates the absolute time of arrival, and Initial Time Delay Gap (ITDG) is the arrival time after the direct sound. The dashed line indicates the absolute threshold of perceptibility after [PERSON]. The solid line is the probable threshold for useful contribution.  
mask the other. Relative reflection levels in the analysis below do not compensate for direction nor overall listening levels.  
Regarding the attenuation of the direct sound, halls with a flat floor will be the most affected by audience attenuation. In the original analysis, [PERSON] used a 15 dB attenuation in excess of the inverse square law based on data from [PERSON] and [PERSON] [23]. The steeper audience rakes are the less affected ones. The following convention has been followed: flat floor \(-\)15 dB (GMV); gentle audience rake \(-\)10 dB (SK); pronounced audience rake \(-\)5 dB (PCH).