## 5 Conclusions  
In situ measurements and perceptual listening tests have been used to investigate the influence of diffusive surface location on the acoustic parameters used in the design process of concert halls and on the perceived acoustic sound field. The case study involved a real concert hall with variable acoustics (ESPRO, IRCAM, Paris, France), where eight hall configurations have been generated by modifying the characteristics of the lateral walls. The objective evaluation has been carried out by analyzing the variation of the ISO 3382-1 [17] acoustic parameters \(T_{30}\), \(EDT\), \(C_{80}\), \(D_{50}\), and \(IACC\) in each configuration, while the perceptual tests have been performed using the ABX method in order to determine whether listeners are sensitive to variations of diffusive surface location. This study gives further insight into the importance of the quantification of the trade-off between the design effort and objective and subjective efficacy of the diffusers application in shoebox halls. The main conclusions can be summarized as follows:  
* The objective parameters are not significantly influenced by the diffusive surface location. No clear trend can be observed for \(T_{30}\), \(C_{80}\), \(D_{50}\), and \(T_{\rm s}\) variations in the different configurations in both the absorptive (-A) and reflective (-R) conditions. \(EDT\) results as the most affected parameter. * The perceived differences between the front-rear asymmetric conditions of the diffusive surface location with respect to the listener position do not show significant differences. However, some of the listeners could still indicate a few differences relying on two or more attributes (reverberance, coloration, and spaciousness). Reverberance seems to be the main attribute when the orchestra and pink noise samples are compared in the reflective condition. Future work should include different hall shapes and volumes in order to have also a more generalized overview of the interaction between room shape and effects of diffusive surfaces. More effort should be put into the investigation of differently shaped surfaces, i.e., different diffusion patterns and scattering values, and different degrees of diffusive surface extensions. More adequate sound sources and reproduction systems might be used in order to have more accurate results although the technical and economical effort for these improvements seems to be important. The findings of this study should be seen as a milestone based on in situ results towards the redaction of reliable guidelines, which could enable an easier design process for architects and practitioners alike. The limited effects of the diffusive surfaces give space to a broad field of design alternatives from the designers' perspective. In this way, there might be more freedom on the aesthetical choices that can be applied to the design of a concert hall once that the acoustic optimal conditions have been obtained. It might be useful to investigate the boundaries of this filed within which the dialog between designers and acousticians would promote further aspects related to creativity. [PERSON] and [PERSON] conceived and designed the data collection campaigns; [PERSON] collected data on site; [PERSON] and [PERSON] performed data analysis; [PERSON] drafted and curated the first version of the manuscript. All the authors revised the paper. All authors have read and agreed to the published version of the manuscript. This research was funded through a Ph.D. scholarship awarded to the first author by the Politecnico di Torino (Turin, Italy). The authors would like to thank all the participants in the listening test sessions for the collaboration. They would also like to express their gratitude to [PERSON], [PERSON], [PERSON], and [PERSON] from the Institute of Technical Acoustic in Aachen, and [PERSON] and [PERSON] from IRCAM in Paris for their technical support and availability during the measurements. The authors declare no conflicts of interest.