Dipoles in frequencies above 65 Hz can have directionality. I own ML IIs, the crossover is at 125 Hz. However, low frequencies do not have directionality. This is not to say that you can not detect where a subwoofer is coming from (one of the myths about subwoofer placement). The lower the crossover frequency the less the ability to detect the placement of a subwoofer. However, the point that was brought up by foreverhifi, regarding dipoles is correct (if I read the original statement correctly). Dipoles in the bass change the speaker power (energy dispersion pattern), but they do not create directionality. This is because the port and the speaker (or speakers--bass only here) are located within 1/8 of a wavelength of the crossover point. The result is a relatively coherent "point source". By point source, I mean you can not detect multiple sources of sound. The ports and dipoles are used effectively for the sound dispersion power, which according to most speaker manufacturers is a good thing (even dispersion). However, new designs, such as Earthworks, are trying to have very uneven dispersions on purpose so that the speaker does not interact with the room as much. I think this whole part has gotten a bit off subject, as the effect of the drop ceiling remains relatively the same for dipoles, bipoles, conventional dynamic speakers and even horms. There will of course be some differences based on the speaker, but it is unlikely these differences would account for very much in terms of the changes due to the dropped ceiling (I hope I stated that clearly).
