As you probably already know, Dolby’s ProLogic IIz audio decoding process adds height channels to the surround sound experience in a 5.1 or 7.1 home theater. Not to be outdone, competitors DTS and Audyssey have developed their own formats that bring us up to 11.1 channels of sound. The question I have is: Do we really need this many speakers, and where will we put them?
To this day, the majority of home theater systems (and theatrical venues, for that matter) are configured in a standard 5.1 layout with three speakers across the front soundstage, two surrounds, and a subwoofer. Most movie soundtracks are mixed this way as well.
A number of years back, A/V receiver manufacturers started adding support for two additional channels, called the Surround Back Left and Right, in between the main surrounds. This helps to fill the gap in the rear soundstage, especially in large listening environments. Audio decoding processes (most notably Dolby ProLogic IIx) were developed that could extract sound cues from the other surround channels and matrix them into the Surround Back channels. The Blu-ray format also includes support for discrete 7.1 sound mixes, though these are still relatively rare.
The home theater environment actually leads the way in developments like this. Discrete 7.1 audio has existed on Blu-ray longer than it has in movie theaters. The Dolby Surround 7.1 format was only recently introduced to theaters last year. ‘Toy Story 3’ was the first movie to support it.
Likewise, height channels made their first appearance in the home, not in professional theaters. Dolby ProLogic IIz can be applied to either a standard 5.1 system or a 7.1 system to add additional height speakers above the front Left and Right. I admit that I was skeptical of the benefits of this (we still have no movies natively mixed with height channels in mind), but I found a demonstration at Dolby Headquarters last November to be surprisingly impressive. In the clips we watched (‘I Am Legend‘ was the primary movie demo), the added channels genuinely helped to expand the soundstage without sounding gimmicky. I still do not personally use height channels in my own home theater, but I’m no longer opposed to the idea.
And now DTS Neo:X and Audyssey DSX give us 11.1 sound. What does that entail? These formats start with a 7.1 configuration and then add two height channels and two new width channels on the sides of the room. The purpose of this is to fill the gap between the front and rear soundstages, under the presumption that there’s currently an audio “hole” there. Again, I admit to some skepticism as to the necessity of this. However, I haven’t heard it demonstrated yet.
My feeling is that this will only be useful in particularly large home theater rooms. I can tell you that in my own HT room, I don’t currently feel that there’s anything missing from the surround sound experience by not having speakers on the sides.
On the other hand, when I spoke to Craig Eggers, a VP at Dolby, a few weeks after my trip to that company’s facility, we had a talk about 5.1 vs. 7.1. I made the argument that 7.1 may not serve much useful purpose in a small home theater room, where there isn’t much of a gap between the main surround channels. Craig then made a case that 7.1 is always useful, even in this type of space. Perhaps these new width channels will be the same way? We may not particularly realize that anything is missing until we actually put speakers there and hear the difference.
Nonetheless, I think that speaker placement is going to be a real issue in most home theaters. I know that I’d simply have no place to put these width channels in my room. I suspect that a lot of people are going to run into that problem.