Arcgeometer is exploring the potential of reactive acoustic systems. Manta is a surface that changes form – and therefore acoustic character – in response to multimodal input via Open Sound Control [OSC], including stereoscopic vision [a hacked Kinect], multi-touch, sound, and brainwaves. Manta explores acoustic variability and responsiveness in the surface itself instead of resorting to traditional applied acoustic treatment. It is comprised of CNC machined panels and connectors of high-density polyethylene. Curved forms result from a combination of triangulation and bending stiffness: geometry and material in concert. It was designed to utilize the rigging infrastructure and acoustically inert environment of the Experimental Media and Performing Arts Center [EMPAC] at Rensselaer.