Much of what worked is below. I think he's absolutely correct that even angle change of a degree can make a major difference.
"Ultimate Soundstage Tuning
The EM-ESL "ultimate" soundstage and imaging have demanding setup requirements. How can one tell if it has truly been achieved? The best answer is achieved with impulse delay matching measurements, using Room EQ Wizard (REW) (or similar analysis program) and a measurement microphone. I got the clearest results with a regular (not USB) measurement mic using REW's timing loopback calibration method, so actual front and rear path delays could be measured directly and arrival times matched to a fraction of a millisecond.
But for a quick means of checking or fine-tuning, a short list of evaluation tracks was chosen, given below along with the particular sonic characteristics to listen for.
Actually, the final treatment method for thickening the soundstage - using horizontal reflection slats mounted along the vertical line below the reflection points on the wall in front of the listener - makes a dense soundstage somewhat easier to achieve. In other words, Example 4 above allows more placement flexibility than Example 3 above, thankfully. With the Example 3 setup, a speaker angle change of less than a degree could make a big difference in the soundstage - from "great" to "average." With the Example 4 setup, such a change would make a noticeable but much smaller difference.
Each EM-ESL speaker had a laser sight mounted on its woofer enclosure using double-sided mounting tape
. A target drawn on a piece of white gaff tape on the room's front wall gave a reference point for checking speaker alignment and for evaluating the change to the soundstage and imaging with minor variations in alignment. The distance from the wall conveniently resulted in a one-inch movement of the laser dot roughly equating to a 1-degree rotation of that speaker.
All placement angles and distances came into play, however, including "pitch" and "roll," which strongly affected image clarity. Impulse diagrams show how the alignment of the reflected rear waves is almost perfect for the "ultimate" effect. That alignment of the reflected waves is what one is trying to achieve. It can be achieved by slight rotation of one speaker or the other or by small amounts of movement of the speaker in the appropriate direction.
The dissipation slats were in place for all of this exercise. An additional impulse diagram shows how their presence affects the reflected signal. The difference appears small, but the sonic result is dramatic.
A detailed alignment procedure will be given in another post."