That's the usual sales pitch/magazine copy, but I've seen a lot of evidence to contradict it. (Yes, yes - I'm sure everyone's just shocked to hear that the admen & reviewers aren't telling us the whole story...
)
I note that you called flat panels here, so apologies for broadening my reply. Best I can see, the air doesn't really care much about
what pressurizes it, so the usual acoustical properties still apply. At the very least, transducer size & baffle width have their effects and limit figure-eight behavior in many dipole speakers. Linkwitz's LX521 & John K's Nao Note have complicated baffles for a reason! John's Tech Studies are comprehensive and daunting;
Figure 3 here gives an idea of how band-limited the effects are.
A few examples:
- The entire 3D3A database! It's small but a treasure. Definitely see the Sanders ESL, which was measured both normally and with back-wave absorption. The frontal-hemisphere behavior doesn't seem to change significantly, though the charts begin at 500Hz.
- Apogee Stage - The pattern widens above the 600Hz crossover, because the ribbon's narrow & baffle wide. 2-pi up to beaming, no?
- AA Beethoven - Linkwitz did a great job with a rectangular baffle 25 years ago. Who has proper measurements of the LX521 to compare?
- Jamo 907 - This one's really interesting, with a 5" mid running 250-2500Hz on a 17" baffle. Above baffle step, the frontal polars look just like similar TMs in boxes. Below ~500Hz, the mid transitions to 4-pi, & we see dipolar behavior that looks like the worst baffle step ever. Also, the rear wave causes the on-axis hole at 1kHz, doesn't it? I suspect a larger driver would average that out a bit, and it will depend on position, just like diffraction.
A lot of these speakers don't have much radiation around 90deg, however, this seems to be a dipole effect only at lower frequencies. The same effect occurs higher up but for totally different reasons, regardless of the type of driver. (I feel the typical subjective reviewer mistakes cause & effect here. Again...) Similar effects certainly can be produced by drivers in closed boxes, but we'll have to compare speakers with identical baffle widths & driver sizes, if we wish to isolate the dipolar behavior.