Sounds not only travel to a pair of ears on a direct path, but they also bounce off objects in the world. Most natural listening environments contain at least a sound reflecting ground plane, such as a floor. Therefore, reflecting objects are necessary to make virtual environments sound natural and realistic. They help listeners navigate and enhance the overall effect of immersion in a virtual environment. Almost as important as reflections, is the absence of a reflection. For example, the brain can tell the change in a sound space when a reflection is removed by opening a door or a window.