Mirage M-1si loudspeaker By Thomas J. Norton   •   June, 1993 I only found out after beginning my auditioning of Mirage's M-1si loudspeakers that the film 2001, A Space Odyssey was, at practically the same instant, undergoing a brief theatrical revival in major cities around the US. I might have known. Perhaps it was the persistent Strauss melodies that rattled around in my head as I set them up. Perhaps it was the two 5'-tall monoliths that subsequently stared at me as I sat in my listening chair. For whatever reason, the M-1sis were an imposing sight, and the association with out-of-this-world events was not a difficult one to make.

True, the shape is by now a familiar one. Mirage released the original M-1 in 1987. The response was very positive—Larry Archibald enthused over the speaker in Vol.12 No.6, June 1989—and gradually a succession of similar tall, black, M-series monoliths appeared in the Mirage line. Now the line is in its second generation—thus the "si" designation. The look is the same for all of them, despite differences in size, driver complement, and price. GL reviewed the M-3si in Vol.15 No.11 (November 1992). Here we examine the newest version of the M-1, Mirage's flagship M-1si.

Externally, the biggest Mirage is virtually identical to the M-1 which preceded it. The M-1si is marginally larger, but you'd have to put the two models side by side to notice the change. The cabinet configuration and bracing are also essentially the same, though the cabinet construction techniques differ. The M-1si is a very heavy loudspeaker, but despite its mass and rather high center of gravity, it is quite stable, even on a carpet of average thickness. Nevertheless, I recommend use of the furnished spikes for enhanced physical and sonic stability.

All of the Mirage M-series loudspeakers are bipolar in design (see Sidebar), using conventional dynamic (cone and dome) drivers. As in the original M-1, the M-1si is a six-driver, three-way system, with identical drive-units radiating to the front and rear. But the drivers in the latest version are all new. The bass and midrange drivers in the M-1si look ordinary enough. The cones, however, are injection-molded polypropylene impregnated with carbon and other materials. This is said to increase strength and rigidity (generally good things) without increasing weight (usually not such a good thing). The 5" midranges, in their own isolated sub-chamber, operate down to 400Hz. The woofers are manufactured by Mirage; the midranges (and tweeters) are made by subcontractors to Mirage's specifications.

The M-1si's crossover network is more complex than that in the M-1, and computer simulation was used in its design. The filters are all second-order, and are conjugate-matched—a technique which preserves (as much as possible) a resistive load at the speaker's inputs. Mirage appears to take particular pride in its new tweeter—used throughout the new M-Series line. The dome is pure titanium with a cloth suspension. Mirage refers to it as a hybrid design (dubbed PTH, for Pure Titanium Hybrid), stating that the combination of materials results in nearly instantaneous transient response with a minimum of resonances or ringing (the literature says that the cloth suspension "prevents" resonances and ringing, but in the real world such a total preventative does not exist). They argue that this new tweeter has the transparency of a ribbon or electrostatic, without overhang. Heady stuff.

As was the case with the M-1, the M-1si is built in mirror-image pairs, with the drivers slightly offset toward the center. It is configured for bi-wiring, with the same type of improved five-way binding posts now found on its less expensive sibling, the M-3si. The M-1si is available only in its striking piano black with black grille finish. Unfortunately, owners of the earlier M-1s cannot get them upgraded to M-1sis; the changes are too extensive.

Setup
I began my listening with the M-1sis set up in the same positions I usually use for conventional, front-radiating loudspeakers. Moving them around in an attempt to fine-tune the response invariably improved some aspects of the sound while sacrificing others. So despite their bipolar radiation pattern, they ended up in the same positions they started in. (This result may have been unique to my room; you should not assume your experience will be the same. Experimenting with loudspeaker placement is always advisable—even more so when the loudspeaker has a dipole or bipole radiation pattern.) This positioning placed them well out from the rear wall and at least 3' from the sidewalls. The current layout of the listening room does not permit easy placement in close proximity to the rear wall (it could be done physically, but the geometry of that wall—with its short, diagonal corners—would make it difficult to avoid other problems), so I was unable to experiment with such placement. But my experience with dipoles suggests that the more flexibility you have in experimenting with position (including the option of setting the loudspeakers up well spaced from the back wall), the more likely you are to be happy with the result. That's not a bad prescription for any loudspeaker, actually, except perhaps for those few specifically designed to operate near a wall.

I began with the Mirages aimed straight ahead, with their tweeters to the inside edges of the asymmetrical baffles. Ultimately, however, I toed them in to face the listening position. This had the usual result—a tighter, if narrower, soundstage. The wall behind the loudspeakers has a large, multi-paned window with drapes which may be opened or closed (visible on the cover photo of our October 1991 issue, Vol.14 No.10). With most loudspeakers, I prefer the drapes open. When I reviewed the original Mirage M-3 (Vol.13 No.11) I found that closing the drapes eliminated a certain graininess from the top end and smoothed the overall presentation. Though the M-1si has nearly the same radiation pattern as the M-3, I found that with the newer Mirage I preferred the drapes three-quarters open. Closing them fully caused a noticeable loss in top-end air and spaciousness.

Listening
The latter characteristic is as good a place as any to begin discussing the M-1si's sound. The superior sense of space a pair of them convey is probably their most appealing and obvious quality. The bipolar radiation pattern opens up the sound significantly. When the pattern is most pronounced, the rear wall behind the loudspeakers simply melts away. But the effect is not always all this dramatic—it is very dependent on the recording. The Mirages, in fact, have a remarkable ability to bend to the demands of the program material, and, unlike most loudspeakers, have a special way with both the intimate and the bombastic. Small-scale program—vocals, small instrumental groups, and the like—sounds appropriately small. Large-scale forces fill the room, but never—at least at any reasonable level—sound oppressive. The selections from the latest Harmonia Mundi sampler (A Decade of Excellence, HMU 10) demonstrated this superbly.