Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2015, Amsterdam Future Visions 17 - 20 August 2015, Amsterdam, The Netherlands A wooden acoustic shell for open-air chamber music concert Eduardo PIGNATELLI 1 , Sofia COLABELLA 2 *, Serafino DI ROSARIO 3 , Sergio PONE 1 , 1 DiARC, Department of Architecture, University of Naples "Federico II" 2 *Gridshell.it sofia.colabella@gmail.com , Vicolo della Quercia 1 – 80134 NAPOLI 3 Buro Happold Engineers, London (UK) Abstract This paper presents the acoustic design process of an acoustic shell for open-air Chamber Music concert, which we refer to as Resonant String Shell (ReS). Each and every part of the shell is made of timber and reversible joints with no glue, thus allowing a simple manufacturing, a sustainable process and a cost effective structure. A sophisticated digital form finding process lays behind such a technologic simplification. It is performed through parametric modelling tools and a multi-objective optimisation algorithm. Geometrical acoustical parameters, such as the number of second-order reflections, are first analysed through image sources technique, and then the Pareto-front of the most performing solutions is displayed. The chosen results are then sent to a more complete acoustical analysis software. Measurements performed on-site demonstrate the quality of the optimization process for both audience and musicians. Keywords: Room Acoustics, Impulse response measurements, Computational design, Acoustics, Multi-objectives optimization, Timber structure, Experimental research, ReS Team. 1. Introduction This paper presents the outcome of a research program which has been developing, since 2012, between Gridshell.it, the acoustic department of Buro Happold Engineers and the Department of Architecture of the University of Naples "Federico II". It concerns the overall process to design and build an acoustic shell (ReS) for open-air Chamber Music concerts, entirely made of sustainable sourced timber produced with a simple manufacturing process, aimed at creating the conditions to enrich the experience of musicians and audience in the most difficult environment: an outdoor space. All parts collaborate in the research program all year-long, in order to develop and design new solutions for ReS that are then tested by parametric modelling tools created ad hoc and by specialist acoustic software, and to finally experience the construction of the entire structure and its architectural and acoustic quality during the Summer School VPM - Villa Pennisi in Musica. In its third edition in August 2014, VPM gathers together more than 130 people coming from different environment, musicians, architects, designers, acoustic engineers, students, who give life to a real formative performance. Music Masters train their musicians apprentices for the concert essays included in the program of the Festival, meanwhile architects, engineers and students flow into the Arch Lab, a workshop aimed to build and then test and verify the improvements of the structure made during the previous years. The most important test is the Opening Concert of the Festival, performed by the Masters under the structure. Here comes the real confirmation of the result of the overall work. Students are involved in the whole process, in order to make sure they can grow as architects, aware of all the intersections between different disciplines in such a complex design, and also to involve