High Efficiency Speaker Asylum: That can be done passively too. by Duke

"The new frontier is DSP-based controlled directivity speakers, which employ multiple drivers and phase manipulation to provide the same directivity at all frequencies, so you hear the same mix no matter where you sit relative to the speakers."

This can be accomplished passively via good radiation pattern control and proper setup (though I would not quite claim "the same mix no matter where you sit relative to the speakers"). Here's how:

Start out with speakers whose radiation pattern is about 90 degrees wide (-6 dB at 45 degrees off-axis), constant directivity (or approximately so), in the horizontal plane. Ideally you want this pattern control down to 700 Hz (like in the JBL M2) but it still works well if we start losing pattern control an octave or so higher.

Then toe the speakers in severely such that their axes criss-cross in front of the center of the sweet spot. You will get good soundstaging and good tonal balance over an unusually wide area. Here's why:

The ear localizes sound by two mechanisms: Arrival time, and intensity. Obviously these will be the same from both speakers for anyone along the centerline, just like for a conventional setup. But in a conventional setup, with little or no toe-in, for a listener off to one side, the near speaker "wins" both arrival time and intensity. So the image pulls in that direction even farther than the listener is shifted.

With speakers having that 90-degree constant directivity pattern AND using the suggested criss-crossing severe toe-in, the situation is very different for off-centerline listeners. A listener off to one side is now very far off-axis of the near speaker, but on-axis (or nearly so) of the far speaker. So the near speaker "wins" arrival time but the far speaker "wins" intensity, at least in that portion of the spectrum where you have the recommended radiation pattern control (which includes that portion of the spectrum most critical for imaging). The KEY is, the near speaker's output must fall off smoothly and rapidly as you move off-axis, hence the unorthodox radiation pattern requirement.

These two different image localization mechanisms will not average out perfectly of course, but you will at least end up with a spread of instruments in between the speakers, and depending on the recording, the center vocalist will usually be somewhere near the center. Tonal balance will be good pretty much throughout the room.

This well-controlled radiation pattern also generates a reverberant field having approximately the same spectral balance as the first-arrival sound, not counting some high frequency absorption from room surfaces. So the tonal balance holds up well no only throughout the room, but often even into the next room!

So imo DSP is not the only way to get good soundstaging and good tonal balance over an unusually large listening area. Some of us have been doing it passively for many years.

Duke