Click here to purchase the entire book in PDF format. Diffuse Field Now imagine that you're in the most reverberant room you've ever heard. You clap your hands and the reverb goes on until sometime next Tuesday. (If you'd like to hear what such as space sounds like, run out and buy a copy of the recording of Stuart Dempster and his crowd of trombonists playing in the Sistern Chapel in Seattle.[Dempster, 1995]) Anyways, if you were able to keep a record of every reflection in the reverb tail, keeping track of the direction it came from, you'd find that they come from everywhere. They don't come from everywhere simultaneously - but if you wait long enough, you'll get a wavefront from every possible direction at some time. If we consider this in terms of probability, then we can say that, in this theoretical space, sound waves have an equal probability of coming from any direction at any given moment. This is essentially the definition of a diffuse field. For a visual example of this, look out the window of a plane as you're flying through a cloud on a really sunny day. The light from the sun bounces off of all the little particles in the cloud, so, from your perspective, it essentially comes from everywhere. This causes a couple of weird sensations. Firstly, there are no shadows - this is because the light is coming from everywhere so nothing can shadow anything else. Secondly, you have a very difficult time determining distance. Unless you can see the wing of the plane, you have no idea how far away you're actually able to see. This the same reason why people have car accidents in blinding snowstorms. They drive because they think they can see ahead much further than they're really able to.