Thank you gene3x.
I’m going to focus on big issues in this post; nothing against refinements, but imo the big issues need to be addressed first.
So here is the big issue when it comes to trying to get a good soundstage across a wide listening area: For off-centerline listeners, the image will be pulled towards the nearest speaker. And the further we go to either side, the more the image is pulled to that nearest speaker. This issue cannot be addressed by incremental loudspeaker refinements; rather, it’s going to take something drastic.
Let’s quickly let’s look at HOW the ears determine the direction of a sound source (I’m going to simplify a little bit). The ear goes by two things: Arrival time, and intensity (or loudness). So if you have two speakers set up normally, maybe with a little bit of toe-in, and you’re sitting in the “sweet spot”, arrival time and intensity are the same for both ears so the image of a center vocalist is right in the middle. So far, so good.
Now suppose you scoot your chair to the left a foot or two. The left speaker inevitably “wins” arrival time because it is now closer. But the left speaker also “wins” intensity, in part because you are closer, but also because you are now on-axis (or nearly so) of the left speaker and quite far off-axis of the right speaker. So the net effect is, the center image shifts to the left even farther than you have!
It is a good thing these two localization mechanisms exist, because they offer us a solution: What happens if the sound arrives FIRST at the left ear, but it’s LOUDER in the right ear? Well, these two localization mechanisms will tend to cancel one another out somewhat, and we can end up with the center vocalist back in the center! Let’s take this information and return to the listening room, and see if we can figure out a way to make the FARTHER speaker the LOUDER speaker.
What I’m going to describe next is not the only possible radiation pattern and set-up geometry, but it works well, and it is what was taught to me by the incredibly smart man I learned all of this from (Earl Geddes).
First, we want our speakers to have a radiation pattern that’s 90 degrees wide in the horizontal plane (-6 dB at 45 degrees to either side of the central axis). Next, let’s use a very unorthodox configuration: Let’s toe the speakers in by 45 degrees, such that their axes actually criss-cross in front of the center of the sweet spot(!). Up and down the centerline, arrival time and intensity are the same, just like before. But off to the side, things are very different.
If we sit to the left of center, the left speaker still “wins” arrival time because it is the closest. But the right speaker “wins” intensity! How is this possible? This is how: We are now virtually on-axis of the right speaker (the far speaker), but we are very far off-axis of the left speaker (the near speaker)! So even from well off to the side we still have a good soundstage with a decent spread to the instruments. The soundstaging won’t be as good as along the centerline, but it will still be enjoyable.
I use this configuration all the time at audio shows. People look at the extreme toe-in and think the soundstage will be narrow but it never is. Whenever possible, I have one chair up against a side wall, beyond the plane of the speaker on that side. People usually avoid that chair but every now and then someone sits in it because the room is so full. I always ask them how it sounds. They are inevitably pleasantly surprised that it still sounds quite good, and that they still hear an enjoyable spread of the instruments.
The KEY to this configuration working as I have described is this: The output of the near speaker must fall off SMOOTHLY and RAPIDLY as we move off-axis. This setup will not work as described with a wide-dispersion speaker because the near speaker will still be too loud.
One way to get this kind of radiation pattern control is to use a low-coloration constant-directivity waveguide-style horn whose pattern is 90 degrees in the horizontal plane, crossed over to a midwoofer at the frequency where the midwoofer’s pattern has also narrowed to 90 degrees. I’m not the first to use this pattern-matching in the crossover region plus constant directivity above it. I think the Altec Model 19 and Model 14 were among the first, followed by the magnificent JBL Model 4430 studio monitor, Wayne Parham’s Pi Speakers, Earl Geddes’ designs, and many modern JBL designs like the M2 and 4367.
Now finally we come around to why a large speaker can do this better than a small speaker: A large waveguide, pattern-matched with a large midwoofer, will maintain our desired radiation pattern down to a lower frequency than a smaller waveguide and midwoofer. But imo unless a large speaker deliberately makes use of its size to get good radiation pattern control, its only advantage over a small speaker would be in SPL and/or bass extension.
I don’t know of any other approach that can maintain such good soundstaging for off-centerline listeners. The near speaker will always “win” arrival time, and the only way to offset that is for the far speaker to “win” intensity. An ultra-wide radiation pattern (like with an omnidirectional speaker) reduces the intensity discrepancy relative to conventional speakers in a conventional configuration, but the near speaker is still louder than the far speaker, so it does not offset the arrival-time discrepancy. Only a fairly narrow, very uniform radiation pattern with that unorthodox criss-crossing geometry does a good job of offsetting the arrival time discrepancy for off-centerline listeners with no downsides.
So why don’t you see this type of speaker and this type of setup more often? Imo it is because the market is dominated by svelte, audio-jewelry, high wife-acceptance-factor speakers, which in turn implies that most audiophiles shop with their eyes moreso than with their ears. How many audiophiles see a horn and immediately form a negative opinion, as if all horn speakers have that annoying cupped-hands coloration? Some do, but the good ones don’t!
Soundstage depth is another topic which I will get into somewhat when I respond to recluse’s request to go into small rooms.
The closest I can come to a specific speaker recommendation would be, used GedLee Abbeys or Nathans + subs, or contact Wayne Parham of PiSpeakers, tell him your requirements including the footprint constraints, and see if he can do a custom adaptation of one of his designs, perhaps a pair of maxed-out 4 Pi’s atop matching subs. Wayne was one of my teachers. In my opinion his designs offer superb value, better than mine. I don’t know how he does it; my suspicion is that his day job pays well enough that his speaker business is more for love of the hobby and the kindred spirits he finds therein than for profit. So between Wayne’s speakers and used speakers by Earl Geddes (Earl has retired), I guess I did end up having some nominations for “best absolute value” after all.
Duke
