Mirage OM-7 loudspeaker
History, theory, and such
In 1987, Mirage debuted the M-1—the first "bipolar" speaker design. What chief designer Ian Paisley did was put conventional drivers on the back as well as the front of the cabinet, and drive them in phase—unlike a dipole speaker, in which the front and back waves are out of phase. The goal, then as now, was to produce a truly omnidirectional radiation pattern—as if the sound was being produced from something like a pulsating ball (it's actually more like a vertical cylinder) (footnote 1).
Obviously, room reflections will play a big part in the perceived sound of such a speaker; this, too, is part of the design desiderata. Mirage believes that the combination of direct and reflected sound, when produced by a truly omnidirectional radiator, sounds more like live music than what can be achieved by forward-firing designs or dipolar loudspeakers, and that the senses of depth and space will be very convincing. Imaging with omnidirectional speakers won't be as vividly precise as with conventional speakers; however, Mirage contends that such hyper-detailed imaging isn't natural or (therefore) desirable.
Mirage's M-series speakers, though quite well-received, didn't completely achieve Paisley's omnidirectional ideal. The problem was that output at 90 degrees off-axis—that is, directly to the side of the cabinet—was somewhat reduced, resulting in a figure-8 dispersion pattern.
The OM series was designed to solve this problem, primarily by moving the front and rear baffles as close together as possible, and by careful design of all other parameters: baffle width, shape of the edge and interface with the grille to make positive use of diffraction effects, selection of drivers and crossover frequencies, etc. The result, as Mirage suggests in the "Technical Overview" document packed with the speakers, is that you can put your nose on the side of the cabinet and it'll sound as if you're listening to a driver that's right in front of you. This is true (I tried it) and not very surprising: you've got a set of drivers right in front of each ear, albeit facing the same direction as your ears instead of at them. It's stereo imaging! However, as you might expect, at this position the highs are somewhat rolled-off. No one said that obtaining purely omnidirectional behavior would be easy.
Audiophiles who've spent significant time and money to damp or diffuse the first-reflection points on the side walls of their listening rooms need to undo their work to listen to the OM-7 as intended. For Mirage, we rewrite the well-known audiophile axiom of "Side-wall reflections bad!" to "Side-wall reflections good!"
If you're familiar with the look of various electrostatic-dynamic hybrid speakers—a thin panel on top, a much deeper box below containing a conventional woofer—then you've got a good idea of what the OM-7 (and its larger sibling, the OM-5, which includes a powered subwoofer) looks like. The top section is shorter and thicker than a hybrid's, with a fabric-covered grille on the front and the back. The grille, though removable, should be left in place—as mentioned above, it's a functional element of the design.
Cherry-veneer columns on each side and a veneered top cap and bottom plate frame the black grilles and black lower cabinet. The front of the bass cabinet has a grille that matches the upper unit's; this lower grille also sports a Mirage logo. Viewed from the front, the OM-7 is quite elegant; from the side, its narrow top and wide bottom give it a slightly ungainly Baby Huey profile.
Around back are four substantial binding posts, knurled for easy finger-tightening (but not application of a nut driver), with unusually burly gold-plated jumpers, removable for biwiring. There are also two ports, one above the other.
Footnote 1: Something that the Ohm Walsh speakers have been doing for many years, and, more recently, certain models from mbl—both with designs very different from that used by Mirage. This is also something that Bose tried to achieve with the original 901.