It is instructive as well to notice how the pressure antinodes of many different normal modes tend to be concentrated at certain locations within such a room. This means that every normal mode of the room has a pressure antinode in each corner of the room . This means, for instance, that if one wants to put sound energy into the available normal modes of a room with maximum efficiency, a corner is the place to do it. Verify for yourself that, similarly, the middle point of any edge of the room is a pressure antinode for half of all the room's normal modes. The elegant simplicity of the well known Sabine equation for reverberation time, is based on the assumption that acoustic conditions are very homogenous throughout the room.
V is the volume of air in the room, and A tot the total sound absorption of the room's surfaces.
Various departures from the Sabine equation's underlying assumptions require various modifications to it. One common example is a rectalinear room in which the absorption is disproportionate for sound moving along certain directions. In that example most of the absorption would be concentrated on sound moving vertically and the Sabine equation would significantly underestimate the reverberation in the horizontal plane. Specifically, and similarly for absorbing surfaces perpendicular to the y and z axes. Note that if all of the surfaces share the same average absorption coefficient then the Fitzroy equation reduces to the Sabine equation.