Click here to purchase the entire book in PDF format. 10.2 Surround From the very beginning, it was recognized that the 5.1 standard was a compromise. In a perfect system you would have an infinite number of loudspeakers, but this causes all sorts of budgetary and real estate issues... So we all decided to agree that 5 channels wasn't perfect, but it was pretty good. There are people with a little more money and loftier ideals than the rest of us who are pushing for a system based on the MIBEIYDIS system (more-is-better-especially-if-you-do-it-smarter). One of the most popular of these systems uses the standard 5.1 system as a starting point and expands on it. Dubbed 10.2 and developed by Tomlinson Holman (the TH in http://www.thx.comTHX) this is actually a 12.2 system that uses a total of 16 loudspeakers. Figure: A 10.2 configuration. The light-gray loudspeakers match those in the ITU775 recommendation. The dark-gray speakers have an elevation of 45$^\circ$ relative to the listener as can be seen in Figure 10.35. The speakers in boxes at $\pm$90$^\circ$ are subwoofers. Note that all loudspeakers are equidistant to the listener. Figure 10.35: A simplified diagram of a 10.2 configuration seen from the side. The light-gray loudspeakers match those in the ITU775 recommendation. The dark-gray speakers have an elevation of 45$^\circ$ relative to the listener. There are a couple of things to discuss about this configuration. Other than the sheer number of loudspeakers, the first big difference between this configuration and the standard ITU775 standard is the use of elevated loudspeakers. This gives the mixing engineer two possible options. If used as a stereo pair, it becomes possible to generate phantom images higher than the usual plane of presentation, giving the impression of height. If diffuse sound is sent to these loudspeakers, then the mix relies on our impaired ability to precisely localize elevated sound sources and therefore can give a better sense of envelopment than is possible with a similar number of loudspeakers distributed in the horizontal plane. You will also notice that there are pairs of back-to-back loudspeakers placed at the $\pm90^\circ$ positions. These are what are called diffuse radiators (although, technically speaking, they aren't diffuse radiators...) and are actually wired to create a dipole radiator. In essence, you simply send the same signal to both loudspeakers in the pair, inverting the polarity of one of the two. This produces the dipole effect and, in theory, cancels all direct sound arriving at the listener's location. Therefore, the listener receives only the reflected sound from the front and rear walls predominantly, creating the impression of a more diffuse sound than is typically available from the direct sound from a single loudspeaker. Finally, you will note from the designation ``10.2'' that this system calls for two subwoofers. This follows the recommendations of a number of people [Martens, 1999][] who have done research proving that uncorrelated signals from two subwoofers can result in increased envelopment at the listening position. The position of these subwoofers should be symmetrical, however more details will be discussed below.