About HOME THEATER SPEAKER SYSTEMS
In a home theater, speakers need to be placed in specific locations. Frequency response and audio localization are greatly affected by where you place them. There is a great deal of academic research documenting this, so consider it a truth. Location, location, location is not just an old saw for real estate professionals.
Let's consider the front speakers first. Ideally, it is best to have left, center, and right speakers of the same type and aligned in a horizontal line through the middle of the video image. Unfortunately, this is not possible in most home theaters because the front speakers would need to go right smack through the middle of the picture. The next best position is to flank the television, or video screen, with the left and right speakers, and install the center channel either above or below the picture. (Note: for those that are building high-end home theaters with front projectors, several screen manufacturers offer perforated acoustically transparent screens so that speakers can actually be placed directly behind the screen. However the center speaker must match the voice characteristics of the l&R speakers, typically by using the same tweeter and mid-range.)
There are several schools of thought about the type and placement of surround speakers, but the most popular is to place the speakers so they are flanking the audience seating area, and somewhat above the listener's ear level. In the days of analog Dolby Surround, there was a general consensus that di-polar (multi-driver, wired out-of-phase) were best for creating a diffuse sound field. In fact, that was, and is, a THX requirement. With the advent of DD and DTS, with discrete L&R surround channels, many began to advocate front radiating point source speakers and surrounds. The problem with this approach is that when mounting as shown in the diagram, the speakers, though excellent at directional special effects, did not do well at creating a diffuse surround sound field, and were identifiable as point sources. Several A/B tests by home theater experts confirmed this. They found that di-polar speakers did a more than adequate job at localized, directional sound effects while otherwise maintaining a diffuse sound field, even with stereo music in the surround channels. THX still recommends dipolar speakers in THX 5.1. The only possible exception would be in a large room where direct radiating fronts could be placed substantially behind the listening position (at least 1/2 the front seating distance.) Finally, one or two subwoofers are a must with todays home theater systems. The LFE (low frequency effects) .1 channel of DD and DTS are simply beyond the capabilities of most woofers in full range front speakers. Even Dolby Surround has bass-laden sound tracks which demand a separate subwoofer. Further, the use of subwoofer(s) can [permit you to buy smaller L&R speakers saving money and enhancing ease of placement.
To finish our thoughts about placement, let's take a look at some common home theater speaker configurations.
In Home Theater Room Number One. In this case we have mounted the di-polar surround channels up on a beam that traverses the room and added a second subwoofer. Alternatively, two speakers matching the fronts can be placed on stands behind the couch.
Home Theater Room Number Two shows a picture tube type television mounted in an A/V furniture cabinet. The center channel speaker is placed on top of the television and the left and right front speakers flank it on shelves. A subwoofer is placed below the television. This may be less optimum for bass reinforcement, but it conceals the subwoofer enclosure and makes the system less intrusive. In this particular room, placing dipole speakers on the walls was not an option because of the window locations, so circular surround speakers were placed in the ceiling.
The last illustration, Home Theater Room Number Three, we show high-end home theater with a large, front-projected video image. Here we have used in-wall speakers around the screen to give the room a clean, theater-like look. There are many manufacturers that make in-wall speakers specifically for home theater applications. We recommend you look at some of the enthusiasts magazines for specific brands.
The rear surround channels are also in-wall speakers. Because this is a high-end enthusiast's home theater room, we put two subwoofers in the front corners for full low frequency capability. Another option is to built the subwoofer's into the walls or into the floor, if you want to hide them.