Speaker… box. These things go together. Right? Very familiar, the speaker and its box, making the type of sound you expect to hear from a speaker. The sound comes from a cone, or a dome, installed over a hole in the box. Half the sound goes forward, toward you, the listener. The other half of the sound goes into the box.
But what happens if there is no box? Sound is created in two directions, forward and backward. Both sides are the same, except they are mirror opposites. In fact, if you could add the front and back together, layering one over the other, they would completely cancel each other, leaving silence!
With sound free to radiate both ways from a no-box speaker, the front and back form a pattern. This pattern resembles a figure-8, or two circles side by side. The figure-8 is the characteristic output pattern of a Dipole Speaker. Just a diagram, but what this shows is the front sound as one circle, like in a bubble, plus the rear sound in another bubble. And what is outside these two bubbles? The front and back are opposites, like matter and anti-matter. They erase each other where they mingle, to the left and right sides of the speaker.
If you listen from the side, at 90° off-axis, hearing the front and back equally, then you no longer hear the speaker directly. In fact what you do hear is surprising, because the sound seems to come not from the speaker but from the room boundary closest to you.
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