It's a wide-range driver and, depending on the application, it can be used down to 300-200Hz. It has an unusual sound; in some respects it's reminiscent of a ribbon & in others of cones. DIspersion characteritics are also somewhat unusual compared to a conventional cone. People who have tried working with it (N Pass is one of these) have had difficulties in getting the speaker system dispersion pattern right (among other things). The side firing mangers seen in some systems are purportedly there to smooth response from ~2kHz downwards...
I forgot: it's also an expensive driver so, if you're thinking of a diy scheme, check out a discussion at diyaudio.com. E-speakers sells it in the US and has some specs at the site.
