Throw some sealed back headphones on and listen for a "image"
Do the sound transducers in any way, shape or form "interact" with each other? Yes, if you have a tunnel through your head they would but for most humans, they generally don't survive that medical issue.
With absolutely no interaction betweent the transducers and no room interaction because they are clamped/sealed to the side of your cranium--why do you get a sound "image or soundstage"?
Now when I listen on headphones, the image seems to be "in my head" (for better or worse)
This is your brain on headphones, any questions?
Now to move on to something more interesting, more 21st Century--imaging from 3/5/7/11/13 channels or even Dolby Digital with 64 main channels. How do they get the speakers right with so many channels or do they have to make different speakers as the channel count grows? How do the speaker companies "know" if the speakers will image properly at 1 meter, 2 meters, 4 meters or 100 meters? They do know that humidity is a big factor with higher frequencies at long distances--does that effect "soundstage"?
How come people can design, build, tune and calibrate speakers as a hobby and have pin point imaging without millions of dollars in test gear? When I built my own speakers for my garage as a "fresh sheet of paper" design, did I know going it what the "stereo image" would be before I cut the first panel, screwed in the first driver or soldered in the first crossover part? Did I "trust my ears" and just throw things together and kept guessing or throwing money at different drivers until I accidentally achieved proper "imaging"? Did I have to build TWO line arrays to test it? Was I lazy and just built ONE of them, measured it out, made changes to the crossover filters or speaker alignment until I had ONE speaker that worked well? Considering each line array had 48 tweeters, 20 mids and 12 woofers that had to be perfectly sealed in to enclosures inside to work properly, was I lazy and just build them one at a time? Why not build two of them wrong then keep revising the design so they worked well enough?
Maybe I should of built two of them wrong--after all, it is only time, effort, money and aggrivation! No, I built one--it didn't work right. I revised it and a month later I had Revision 2--and it didn't work right. Back to the books I went--a few months later came Revision 3 and it worked well enough. I then built the second speaker and duplicated the first. As a pair, did the oddities I noticed with Revision 3 speaker change...at all? No, not with my human hearing and my test gear informed me it was still flawed. I then spent time, effort and aggrivation fine tuning the crossover filters, making sure all those drivers were sealed and cheated--I used EQ because that "fixes" some issues inherent with line arrays. I listened, it sounded "correct" (except for one minor issue) and the measurements told me I got close. Only took me 18 months, three revisions, way more testing and far more reading about how arrays worked than I liked but that is the point of the hobby--to challenge yourself and learn something!
The imaging? Well, with over 160 drivers operating for the pair and considering they are almost 8 feet tall sitting on low height subs--they have a very wide horizontal dispersion (100 to 120 degrees) but a vertical dispersion of less than 10 degrees to prevent floor/ceiling bounce in a garage (why I built them) The image sounds BIG--really big... it is a line source, not a point source at least at distances up to 4 meters--after that it then reverts back to a point source--just to be scientifically accurate. The system is a "2.2 channel" in that it uses subwoofers, I require proper bass management because it being an "active garage" I am limited in placement and riding lawnmowers, BBQs and toolboxes are not acoustically friendly devices. Most people comment on the things, they tend to dominate a space by sheer size--they always call them "big sounding" and have fun moving forwards and backwards in their nearfield and note the SPL varies little, notice as they move backwards the sound changes again and it becomes "normal" at around 8 meters back. To them, it is a very odd feeling but I know why and will give them the information if they really want to know. I then flip one of them on saw horses pointing straight up and tell them to walk beside it and listen to the sound. Once they reach the end of the array, they physically are past the drivers--the sound SPL level plummets "Like someone closed the door". You would think dome tweeters have a very wide dispersion, they do but not when you stack 48 of them together squeezed in tight. If they want to listen to them positioned vertically, the subs are 20 inches tall where the arrays are placed and they can lay on the floor and notice the very sharp vertical cut off.
I will never build such things again--but the teenagers love the things (bigger is better and more drivers look cool!) They also learn the rules of acoustics just by listening and playing around with the things. No reading, understanding, effort or critical thinking required--teenagers like that!
I like to throw the 1812 Overture in those things as an example why I went through all the hassle to build them--the wall of sound effect. To keep the audiophiles at bay, I call them a "pro sound design" to avoid "improving them" with amps, cables, wires, DACs, record players and any Audioquest, Kimber, Monster, Cary Audio, PS Audio and other consumer sound black hat quackery. It is a pro sound design, you automatically think those suck anyway so no point in jibber-jabber, sit down, shut up and grab a beer--this mess was made for fun! It is not a HT system, it is a garage sound system to play tunes when I'm working on real life stuff, the room is not allowed to change and it does sound better after a brew or two.
I don't have to worry about the "last 1%" of my HT system equipment--my room acoustics would improve more with a few acoustic panels and better placement--but it being a living room is priority so I have a natural stopping point. The garage system is done! Well, "donish" because I am seriously considering building a tapped horn--8 feet tall and bulletproof just because I want a tapped horn to play with. Being a garage system that has no limits on size, WAF or shiny abilities--big, ugly and raw is the man cave style. The arrays are done but there is always room for more Jello....errr, more subs! Now I just need a "reason" to waste more money, time, effort and space--more subs = better bass accuracy across larger areas--that will do it! Must have a "reason" to blow money on a first world hobby that really does not impact the rest of the world. Any time I get a crazy idea about "improving" the arrays with better mids (Qty 42) or better tweeters (Qty 96) I vividly remember soldering all that stuff together and the huge looms of wiring that resemble a telephone connection room in a major building--my inner hatred for such an undertaking takes over and I pass. Those things are done, they will always be done... play with subs and EQ. I have found the personal limit of my hobby!
In short, using the famous words of a talented philosopher (The Cranberries) It's in your head, in your head....zombie, zombie, zombie! (brains!) Ponder how headphones work... 18 has left the building!