Mirage OM-6 Loudspeaker

      Date posted: April 24, 1997

Mirage OM-6

Sugg. Retail: $4000
Size 45 1/2″H x 9 3/4″W x 16 1/2″D
Manufacturer: Audio Products International
3641 McMicoll Ave., Scarborough, Ont. M1X 1G5
(416) 321-1800 FAX 321-1500

(Reprinted from the Spring 1997 Audio Ideas Guide)

     It’s been a while since Ian Paisley, arguably the dean of Canadian speaker designers (but definitely no relation to Ulster’s rabble-rousing reverend) has introduced a breakthrough design, but here it is in the new OM-6. Described (and trademarked) as Omnipolar (Ian still regrets not registering “Bipolar”), this new speaker looks rather like a an electrostatic panel on top of a subwoofer, but it is a fully dynamic design, with double midranges and tweeters in the upper panel, and powered side-firing woofers below in a sealed cabinet. Both enclosure sections are largely clad in black cloth with a piano-black top piece and gold plated feet.

     The tweeter is the 1″ “PTHTM Pure Titanium Hybrid” dome that is also used in the M-1, while the midrange is new, a 5 1/2″ driver “with mica filled injection-moulded polypropylene cones, butyl surrounds and polymer baskets.” The woofers are described as “heavy duty twin 8″ long-throw subwoofers mounted on opposing sides of the enclosure,” driven by “a Mirage-engineered 150-watt dual-module MOSFET design” amplifier. Level and bass contour controls are on the sloping rear panel of the subwoofer system, something I’ll elaborate on when discussing the measurements. Both line-level and speaker-level inputs are provided for the sub module, the latter recommended on an accompanying card to provide the best sound the line input would provide purer sound and better utilize amplifier power, since in the most power-hungry frequency range you’d avoid having one amplifier driving another. More on this below.

     The OM-6’s midrange drivers and tweeters are arranged so that the back of each former faces the back of each latter, with tweeter at bottom at rear; this is both so that they can be fitted in such a shallow enclosure, the two midranges deeper than the tweeter, and to provide polar radiation patterns with minimal lobing, that is, acoustic interference, to maintain true omnidirectionality. The 4 1/2″ depth is important because it is shorter than most midrange wavelengths, thereby allowing the system to be omnipolar rather than bipolar (with significant side nulls). Since the baffle is narrow, at under 10″, both diffraction and front/rear driver interference are minimized here, too. A circular acoustic lens is fitted to the tweeter to also aid in this regard.

     Looking at the measurements, we have a few more than usual to decipher, and we’ll have to approach them in a slightly different manner. The 3 Pink Noise Sweeps at top whose traces diverge in the bass region show the aforementioned adjustments. The one at top below 100 Hz shows the subwoofer volume setting at its highest level, while that below shows the contour control cranked all the way. Note how the speaker in this setting rolls off quite quickly below 50 Hz; some users might prefer this position for rock music or home theatre. The bottom of this trio shows the contour at its lowest setting for flattest, most extended bass, and indicates the true capabilities of the OM-6 in the bottom octaves. Our level and contour settings for the other measurements were the result of experiments for flattest response, and ended up quite close to the lower one in level and contour adjustments.

OM-6 Frequency Response      Below are the normal Pink Noise Sweep (PNS) and Summed Axial Responses (SAR), an extra PNS done from the rear which (for reasons I’m not totally sure of) had 2 dB more energy in the bass; they are otherwise virtually identical. The smoother SAR that overlays these indicates by its similarity the omnidirectional character of the speaker, showing just a little more upper octave power when we add the axial curves together.

     Below, the quasi-anechoic measurement shows very smooth response on the speaker’s direct axis, with a somewhat subdued midrange, a characteristic seen in all other measurements, with a very linear, extended top end; most tweeters tend to slope more above 10 kHz, but this one, just like the Energizer bunny, just keeps on going.

     In the axial curves the trends continue, demonstrating the overall consistency underlining the OM-6’s omnipolar design. However, a degree of side lobing cancellation can be see at 60o between 1 and 3 kHz, this probably a good thing, as it wll control early side wall reflections without affecting those wanted ones coming milliseconds later from the rear walls behind the speakers. Does this 60o null mean that we’ll have to describe this speaker as “Semi-Omnipolar”? You might want to trademark that, Ian, just in case. But, on reflection, I still think OmnipolarTM is a quite fair description of the OM-6.

OM 6 Impedence Curve      Though no crossover points are offered in the spec sheet, the impedance curve suggests that the pair of 8″ drivers are crossed over at about 80 Hz, this putting quite a load on the 5 1/2″ midranges. Below this frequency the impedance rises rapidly, reflecting the typical high impedance of the sub amplifier input and its buffer to protect the outboard driving amplifier (that is, the one in the system that drives the midrange and tweeter). In the mid-bass/lower-midrange, impedance reaches a low of 4 ohms near 300 Hz, but still shouldn’t be too hard a load to drive, being above 8 ohms above 1 kHz. The electrical phase shift through crossover seen below is quite modest, something that is quite important in an omnidirectional system, which has to be both electrically and acoustically phase coherent to avoid driver interactions that would cause cancellations, the only one being that seen in the midrange at 60o in the axial frequency curves.

     Judging by all the measurements, the OM-6 should provide both a big soundstage when properly placed in the room, and precise lateral imaging. In listening, of course, I was able to directly compare it with the Energy son-of-flagship forward-radiating Veritas v1.8. This proved to be very interesting indeed.

     I guess I’d have to characterize the Energy as the more accurate speaker in the classic sense, but the Mirage supplements its mild midrange reticence with a very big soundstage beyond and behind the speakers that offers a wealth of musical information. Imaging is very precise laterally, and the depth and breadth of the soundstage and ambient field very similar to what I’ve been hearing for 20 years or more in concert halls. Of course, I can get a similar effect using my ambisonic processor with an additional pair of speakers (ADS 300W), and one that extends to behind the listener, but that’s an unfair comparison, so I left them off when switching back and forth.

     My notes describe female voice as “very clear, articulate, with a hair of extra sibilance” and “a big ambient presence.” Acoustic guitar was “very clean, a little mellower than with some speakers.” These pretty much describe the fairly laid back sound of voices and instruments in a big wide and deep soundstage. String sound was “very natural and sweet” (I guess I’m quoting listening notes more here because the OM-6 inspired my muse more than most speakers), and the OM-6 was “very good at revealing nuances back in [the soundstage.”

     I find most bipolars have a slightly unnatural sense of depth, and this tendency (one that is particularly noticeable to those who make recordings and have heard the spaces where they are made) was much reduced, perhaps due to the minimum of driver interaction cancellations. I could live with this version of enhanced stereo because it is so revealing, rather than providing concealment of the real soundstage.

     Getting away from imaging and turning to dynamics, the OM-6 will play louder than any speaker in recent memory except the Waveform Mach 17 (Wtr 97), especially in the bass. It never seemed to run out of gas even at the lowest frequencies. What did run out of juice was our amplifier, which at well over 100 dB started to clip (and the sub’s internal amp, with about the same power, may have, too), so buyers with large rooms should think superamp.

     Of course, I was driving the sub amp from mine, as per the attached instruction card (it had punchout holes and was pushed onto each speaker’s level and contour knobs). I still think a better use of amp power would be to use the line-level inputs for the sub, thus avoiding having one amplifier driving another amplifier, which seems to me like wasting half your available power.

     However, when I tried the alternate hookup, carefully switching the bass input to line, I got some pretty large sparks when hooking up to the OM-6 terminals, and decided, in the interests of not having my 20-year Bryston warranty negated by carelessly blowing my third amp channel in a year (I fried the other two with subwoofer hookups, too), that I would abandon this attempt. A quest for power efficiency was becoming a bit of a blowup (AAM will address this subject in his followup in Vol.17 #2).

     Nevertheless, the Mirage OM-6 still ranks as one of the most innovative and interesting speakers to come through our testing and listening process, one with remarkable realism, lifelike dynamics, and a degree of spatial re-creation that will appeal to many high end audiophiles. The buzz among early listeners is that it’s better than the M-1si, and I’d be inclined to agree. The OM-6 is certainly less likely to dominate a room visually, though it can certainly do so sonically.

Andrew Marshall

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