The concept of a loudspeaker with its own built-in amplification is an idea whose time should long since have come. Technically it makes a lot of sense, and in some parts of the world—not to mention professional circles—it's quite popular. But commercially, the idea has never really taken off in this country. And while the loudspeaker manufacturer should be in a better position to make the best amplifier choice, American audiophiles seem wedded to the idea of making their own amplifier/loudspeaker match. The current popularity of subwoofers, however, may have inadvertently sown the seeds that will change all that. It has given rise to an interesting and sensible hybrid: a one-piece loudspeaker whose woofer is separately powered from the rest of the system. The user provides the amplifier to drive the midrange/tweeter portion of the loudspeaker.

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Such a system has a number of advantages. First, the woofer amplifier and driver can be tailored to each other.

The power output of the amp can be designed to complement the power handling and sensitivity of the woofer, and low-frequency equalization can be used if needed. There is also the possibility (though not a guarantee) that such a direct connection to the driving amplifier will offer better control of the woofer's performance. Second, the woofer crossover frequency can be lower. A passive crossover at or below 100Hz—particularly the low-pass leg—has a number of serious technical liabilities. Third, the bass characteristics and power output of the amplifier the user must furnish become less significant, allowing the user a potentially wider selection of candidates (but see more on this below). And, finally, the powered woofer allows for user adjustments—woofer level and perhaps contour—that are not feasible in a passive design.

Mirage is not the first company to come out with such a powered, self-contained subwoofer design, but this feature, significant as it is, is not the only attraction of their new OM-6 loudspeaker. This model also incorporates a number of concepts that Mirage has used successfully in earlier bipolar designs (some of which remain in production), and at least one new refinement on the bipolar principle. Recall that both bipolar and dipolar loudspeakers radiate energy front and back. Bipolar loudspeakers (invariably designed around conventional dynamic loudspeaker drive-units) differ from dipolar designs (often, but not always, flat panel radiators) in that the front and back radiation are out of phase in a dipole, in phase in a bipole (which means that the cones on both sides move away from the cabinet when presented with a positive voltage step). In a dipole, there is a deep null in the sound output at the sides of the enclosure due to cancellation of the opposing phase wavefronts. In a bipole, the response dips at the sides due to the natural limits of driver dispersion at higher frequencies, but the front and back radiation do not cancel each other out.