Furthermore, let us also assume that we will be using the software or barrier Ambiopole arrangement for the left and right front channel speakers which are separated by a ten degree angle directly in front of the listener or listeners as described in more detail in Chapter 7. This is desirable because no practical room treatment is ever fully absorptive, so the less there is to absorb in the first place the better the result. In a multi-speaker surround system there is also the possibility of significant reflections from the surround speaker cabinets, diaphragms or frames so room treatment is even more desirable in such systems. Since so many of my readers are devotees of video home theater and its ad-hoc arrangement of two surround speakers placed at the rear sides, I think it would be best to first discuss the shortcomings of this arrangement before proceeding to describe something more realistic and scientifically based. The home theater movie people recommend two dipole speakers placed on edge so that the acoustic null such speakers produce is facing the listening position.
Dipole speakers are speakers that radiate sound equally from opposite sides.
Additionally, these sounds are of opposite polarity and so cancel where they collide in a room. Some dissenters argue that monopole, that is direct, single polarity, radiators, are better. Either type of rear surround speakers may be reasonable some of the time for movie and video sound reproduction. The use of dipole speakers assumes that the listening room is quite live, because otherwise, the dipoles would be relatively inaudible. But a live home theater room means that the direct sound from the front speakers will be reflected, in spades, from all these nearby surfaces, especially since there are three of them up front emitting direct sound.