A few things to consider.
- The "longer" a room is down from the Screen wall and as opposed to width, the more essential additional surrounds and rear subs become
- 9.1 systems are based primarily of Rooms requiring additional Sound Staging across the width of the Screen wall. Yamaha pioneered this kind of "Consumer-oriented" planning with 7.1, employing the extra "effects" channels between the Center & R & L mains or to each side of the mains. They continue on to this day with 9.1 & 11.1 systems designed along that same premise.
- Despite conventionally held beliefs, a longer room is really not an ideal choice...just status quo. Deep rooms are "people Palaces" allowing mutli row-multi level seating, but they ARE NOT rooms engineered for accurate staging of multi-channel sound. Look to a wider, rectangular shape for the best effect.
- Increased distances between speakers require the patterning of dispersion so as to effectively blend the sound image seamlessly and reduce the need for Delay to offset adverse characteristics created by increased distance between Drivers.
- If you possess or obtain Dipole or Tripole design Surrounds, the additional 'multi-directional' drivers are specifically designed to disperse the directional nature of the sound and create a larger, more expansive sound stage. With less "holes"
- As previously stated in a post above, additional Subs are a cause to an effect; that is to produce a more evenly distributed Low Frequency wave throughout the room, one that saturates at controlled levels that blend with ALL other content.
- Such a "Sub-Bass Blending" reduces (does not eliminate) acoustical concerns, as does correct speaker placement/design.
- Multiple Channel design is intended to address the last point more than anything else, simply because muti-channel sound stage imaging depends upon a smooth transition of effects between the various sound sources.
- Design a room, (or have to deal with a room) that is "deep" and it becomes difficult to balance. Harder to get a expansive Front Sound Stage across a narrow point of presentation. Harder to fill the room with equalized Bass from a "forward" only location. Harder to correct for "imaging holes' by using delay.
- Basically, what is being done is a drive toward saturating a room with many drivers, all intended in improving distribution of sound across a larger area.
- 9.1 on up systems will still depend upon "matrixed" not discreet content when they go beyond the number of channels "mixed" at the Engineer's console. Just as it was and still is with 7.1, there is always a minimum of a 2.0 gap between current "mixing" technology and Consumer oriented equipment.
- As more and more "Normals' opt for a true Theater Design, acceptance of such "many multi-speaker" designs become more easy to swallow.
So in all this one can conclude that if you have a room that is 2x deeper than it is wide, additional surrounds / Subs are not just desirable...they become essential of create acceptable Surround Sound imagery. Not much however can compensate for smaller "Visual' imagery if one gets to the Show late and must sit in a recessive rear seating location if the screen size is likewise restrained in size. Nor will a truly epic sweep of sound occur in the transition of mixed effects if there no distance between the Center and R & Left mains.
The last posted example just above this Post validates that viewpoint, where it is seen how the "effects" speakers serve to fill in a gaps between the actual "imaging Drivers' with additional ambient matrix-ed produced "fill'. That sound is NOT however "discreet' programming. Personally speaking, that diagram is simply a illustration, and most assuredly NOT a well thought out room designed for optimal performance. (note the "plasma-sized" screen
) I don't think I've ever seen a diagram that was such...from any Mfg. All are horribly outdated and represent anciently held conventional design.
It's humorous to note that in the 90's when far fewer people considered owning a Home Theater and had to deal with using wider Family rooms, 7.1 systems (matrix induced effects oriented) came about to lessen the "gap" between anemic R & L mains and the ever present center. Now with a lot (too many unfortunately) of willing converts being led by the nose into employing 80 year old Theater design because it "seems" to be what everyone has always done, an ever increasing number of channels is becoming more acceptable....and necessary.
I installed my first 3.0 Dolby system in 1979 (Stereo w/Dual matrix-ed "Mono Rears") while using the TV speaker as "Center" and a Under Floor mounted Bass Tactile system (for a Sensurround effect) I just knew instinctively that Star Wars and Alien would be coming "Home" to us all soon and Stereo alone would not suffice.
Today I've progressed to 7.6
Center - R & L mains - R & L Side Surrounds - R & L Center Surrounds - Twin Subs Forward for LFE (.2) - Twin Dual Voice Coil / Dual Amp Subs for reproduction of Bass from Side Surrounds and Center Rear Surrounds (.2) and In Floor-In Platform Tactile Bass Transducers for additional LFE supportive effects. (.2)
7000 watts total in a 24' wide by 21' deep room is my current "maxed out system. 122" diagonal screen, w/seating for 12 in two rows.
Conventional wisdom can be terribly myopic, and Promotion oriented "advances' terribly misleading. Consider everything you think you "know' and then consider that insufficient and outdated. Then you'll be open to what can be really accomplished. Exorbitant amounts of cash has never been the real need...just effective design from start to finish. Cash simply helps accommodates poor design. Or the Ego.