Eldartford,
Before I begin, let me admit that I have been an Active speaker user for 15 years (Meridian) and a Meridian DSP speaker user for the past year. I drank the whole jar of Kool-Aid. With that disclaimer:
In fact, Monoblocks are not at all the same as powered speakers. Passive speakers receive a large electrical signal from an amp, through their crossover (single driver units, like Lowthars, being the exception). Since the signal is large (compared to the line level signal received by the amp) the crossover has to be large. Large, high quality components are expensive. Large chokes and caps, etc. must be must be used. Since it's passive, the crossover can only "throw away" power to provide proper equalization to the various drivers (can't add it). Crossovers are notorious for adding phase anomalies and can introduce a wide swing in speaker impedence versus frequency, making a speaker difficult to drive. Since the crossover must "throw away" power to equalize a speaker, power is wasted (sometimes a LOT of power).
Active speakers, on the other hand, receive a line-level signal into a small, active crossover, where impedence is a non-issue (line level impedence being 100x or more that of speaker level impedence). The signal is split actively to one amp per driver (or driver type). These amps are sized specifically for and connected directly to the drivers, which present a much more level impedence to the amplifier. Damping factor, efficiency (and usually dynamics) are improved. Because damping factor is greatly improved, cone control is improved, allowing the active speaker to control large driver excursion and reach louder volumes, frequently with smaller drivers. The distance between amp and driver, combined with the even impedence curve, make (internal) cable selection much less critical (obviously, one can not choose traditional speaker cable for an active speaker).
The next step, of course, is a DSP speaker, but I won't get into that here.
I recommend that those interested in this topic read Bob Stuart's (Meridian) white paper at http://www.meridian.co.uk/w_paper/DSP_speakers_scr.pdf. Bob has been a pioneer in active speakers since the '70s. Today, most Meridian speakers go a step further than simply active, maintaining a digital signal all the way into the speakers, but the white paper has a lot of great information about the advantages of active speakers in general. It's an interesting read.
As I see it, the real disadvantage of active speakers is that they restrict the user's choice. I, for one, am happy to have a custom-tailored amp/speaker interface, but I know that many hobbyists want to choose each system component individually (hence the seperation of DACs from transports, phono stages from preamps, etc.) certainly, active speakers remove some of the ability to "tweak" a system. As an obsessive/compulsive hobbyist with enough to obsess about already, I welcome the simplification.
