@fleshler mentioned his "10 foot wide good sound criteria."
There is an unorthodox technique which can give you good tonal balance over a wide area, and even pretty good soundstaging, though the soundstaging will still be best up and down the centerline.
The basis is this principle of psychoacoustics (which I’m going to simplify a bit): The ear/brain system localizes sound by two mechanisms: Arrival time and intensity. We can take advantage of this to still get a decent soundstage even if we are well off to one side of the centerline.
Let’s first look at a conventional setup. Imagine you’re sitting in the normal sweet spot, speakers facing approximately straight ahead, maybe toed in a little. Perhaps the speakers are ten feet apart. Arrival time and intensity are the same from both speakers, so imaging is good.
Next shift your listening position five feet to one side. The image shifts all the way over to the near speaker. This is because not only are you now much closer to the near speaker, you are also on-axis of the near speaker (or very close to it) and very far off-axis of the far speaker. So both localization mechanisms favor the near speaker. In fact if you only shift partway over, the center vocalist’s image usually shifts farther than you do.
Now let’s try something totally different: First, we start out with speakers that have a very specific radiation pattern: The radiation pattern is 90 degrees wide in the horizontal plane (-6 dB @ 45 degrees off-axis to either side), and this pattern is pretty much constant over as much of the spectrum as is practical (down to 700 Hz would be nice, but down to 1.4 kHz still works well).
Second, we toe those speakers in severely, like maybe 45 degrees, such that their axes actually criss-cross in front of the central sweet spot. Yes it looks weird, but stick with me.
In the central sweet spot, arrival time and intensity is the same for both speakers. But now let’s move over five feet to one side...
Now we are sitting directly in front of the near speaker, so it "wins" arrival time. But we are also very far off-axis of that near speaker. We look over at the far speaker, and by golly we’re just about right smack on-axis of the far speaker! And so the far speaker "wins" intensity! These two psychoacoustic localization mechanisms balance out somewhat, so we still end up with a decent spread of the instruments. Depending on the recording and a few other details, the center vocalist may still be fairly close to the center. Now the soundstaging isn’t going to be as good as it is up and down the centerline, but it’s going to be way better than what we had with a conventional set-up.
The KEY to this working well is, the output of that near speaker must fall off quickly and smoothly as we move off-axis, at least in the mids and highs were we get most of our imaging cues. This crossfiring setup doesn’t work very well with conventional speakers because they don’t have the right kind of radiation pattern - the near speaker’s off-axis response is still too loud.
At audio shows I try to set one chair up against a side wall, actually to the outside its nearest speaker. When the room is full and someone is forced to take that seat, I give them a couple of minutes there and then ask how it sounds. I’ve never had anyone be anything other than pleasantly surprised at how good it sounds even from such an extreme off-centerline location.
Another advantage of this configuration is, considerably more uniform tonal balance throughout the listening area. In particular, the cross-firing configuration results in a more uniform distribution of the highs, so nobody gets cheated in that regard.
One more advantage of this configuration is, it minimizes detrimental early same-side-wall reflections. The first significant sidewall reflection for the left speaker is the long across-the-room bounce off the right side wall, and vice-versa.
There is a slight trade-off: Best imaging for one person in the sweet spot is arguably a bit better with the speakers aimed right straight at the listener’s ears, or maybe aimed at a point a foot or two behind the listener’s head. Some taming of the top-end energy may be needed, as now you are directly on-axis of both tweeters, whereas with the criss-cross setup you are never directly on-axis of both tweeters. The tonal balance will also be less consistent throughout the room when the setup is optimized for a single listener.
So if your priority is "10 foot wide good sound", imo it can be done with the right kind of speakers in the right kind of configuration. Examples of speakers that can do it are the JBL M2 and 4367, the PBN M2!5, anything by Earl Geddes, most models by PiSpeakers, and most of my stuff. I’m sure there are others that don’t come to mind offhand.
Duke
