Posted by Wayne Parham on July 19, 2003 at 10:22:30

In Reply to: Re: Boundary conditions and room interactions posted by Adrian Mack on July 19, 2003 at 05:48:00:

Free space (4π) is open air, where sound can radiate omnidirectionally without hitting a nearby boundary. Half space (2π) is a ground plane, confining a sound source to radiate only into a hemisphere. Quarter space (π) is a ground and a wall, so the sound can only radiate into half a hemisphere. Eighth space (π/2) is a trihedral corner. There are also boundary conditions more constrained than eighth space, any angle more narrow than a trihedral corner.

The more confined the radiating angle, the higher the directivity of the wavefront. In a sense, the boundary conditions act like a waveguide, defining the radiating angle. However, this is only true if the sound source is omnidirectional to begin with, the hypothetical pulsating sphere. In practice, sound sources are not that way, and have complex directional characteristics of their own. If the sound source is already more directional than the boundary conditions it is radiating into, then it might as well be operating in freespace.