I don't think any speakers with flat response are actually flat enough in exactly the same way to sound the same. "Ruler flat" is coming up regarding speaker frequency responses, but I've never seen ruler-flat graphs in regards to speakers.

I disagree. Speaker measurements are typically taken by a microphone placed one meter from the baffle. A microphone can only measure the sound that hits its diaphragm. At one meter away, pretty much all that sound is direct. At a typical listening distance, the sound of a speaker, to a human ear, is the sum of all the auditory information reaching your ear. This includes all direct and reflected (from the floor, ceiling, walls, furniture, etc) sound information.

Unless you're in an anechoic chamber, I'd say two speakers that have virtually identical response curves -- even on-axis and off-axis measurements -- might easily have distinguishable differences.

If the speakers are identical at 1m to a microphone, and have identical off axis responses, curves, and efficiencies, they should sound exactly the same in the same room with the same equipment and same placement.

The thing is, you're taking a narrow snapshot of a speaker's total dispersion pattern when you sample at, say, only 0°, 30°, and 60° -- all in the same horizontal plane.

Yes, but we both agreed to identical off axis, right?

I have to side with Steve on this one. Of course, it's a rather academic question, since no speaker truly has absolutely flat response.

Maybe this would fix the problem.

Yes, and no two speakers are truly identical in efficiency and off axis response. But given 2x6's comment, if there were 2 manufacturers with truly identical speakers in every measurement, I would expect them to sound the same.

Read my sig.

If every measurement you took on two separate speakers was identical then I, too, would say they'd sound identical. I admit to taking a very critical academic stance and saying that the standard on-off axis measurements taken in one plane at 1 meter are likely not enough to rule out other possible differences.