Computer aided acoustic design of concert halls

Twenty years ago, the Radit2D program offered acousticians an interactive tool to design the shape of a room cross-section with the first reflection. Based on the method of images, it was enough for the sequence of straight-line segments drawing the enclosure to follow a regular curve for its orthotomy to appear by connecting the points of the image. This new curve quickly appeared as a guide, especially when it was necessary to direct the sound energy toward a particular area of the room, without focusing or dispersing it. We then studied the logarithmic spiral, the best candidate to assume this role, typically for the acoustic ceiling of a large conference room. Recent advances in raytracing techniques, with extremely fast shots computed directly in the CPU, now allow us to provide a new representation of the set of specular reflections in three dimensions, not only for a particular receiver chosen from the public, but also, and simultaneously, for the entire concerned public. This makes it possible, for example, to find the ideal shape of a concert hall, as complex as it may be, which guarantees for the whole audience the best possible compromise between reverberation and Lateral Energy Fraction.