Mirage M-790 Floor standing speakers
The M-790 is one of the loudspeakers in Mirage's Bipolar series. Like the company's top-of-the-line M-l, the M-790 was designed to produce a spacious, 360-degree sound field in the listening room. The bipolar effect is achieved by a combination of front and rear radiation to generate similar sound fields in front of and behind the loudspeaker over a major portion of the audible frequency range. Although this pattern superficially resembles that of a dipole radiator (a figure-eight with identical responses to the front and rear), there is a fundamental difference between the two. The two lobes of a dipole radiator's output are 180 degrees out of phase, with output nulls to the sides. The bipole outputs, on the other hand, are in phase with each other and generate a sound field over a full 360 degrees around the speaker (although it is not actually omnidirectional, this pattern does achieve some of the subjective quality of an omnidirectional radiator).
The M-790, which actually has three drivers, could also be described as a "two-and-a-half-way" loudspeaker. It is a compact floor-standing system with two drivers near the top of its front panel. Uppermost is a 1-inch titanium-dome tweeter whose diaphragm and voice-coil bobbin are formed from a single piece of metal. The dome radiates through a ring that reduces its effective diameter; Mirage calls this a "time domain equalizer" (TDE) and says that it enables the tweeter to combine the wider dispersion of a 3/4-inch dome with the extended low-frequency performance of a 1-inch dome.
Immediately below it is an 8-inch woofer with a polypropylene cone and rubber surround. The woofer, which operates up to 2 kHz, is in a vented enclosure occupying most of the cabinet's internal volume. It has two ducted ports opening to the front and rear of the cabinet. The opening of the front port is sculpted to reduce air turbulence (the rear port is not so treated, possibly because any turbulence-induced noise from it would probably be inaudible in the listening area of the room). The enclosure, made of 3/4-inch medium-density fiberboard (MDF), is rigidly braced and internally damped. The speakers are supplied with spikes for optional use on carpeted floors.
At the top of its back panel the M-790 has a 4.5-inch polypropylene-cone driver that Mirage calls an MSE (Mirage Soundstage Enhancement) transducer. The MSE reproduces frequencies from 450 Hz to 10 kHz, creating the rear half of the bipolar sound field in that range.
The M-790's rated on-axis frequency response is 36 Hz to 22 kHz +/- 3 dB. At 30 degrees off-axis, the upper limit is specified as 18 kHz. Sensitivity is rated as 87 dB, impedance as 6 ohms nominal, 4 ohms minimum. The speaker is recommended for use with amplifiers rated to deliver between 50 and 150 watts.
The removable grilles covering the upper portions of the front and back panels are firmly retained by plastic fittings. Their cloth exteriors are mounted to half-inch-thick wooden surfaces cut out to enclose the rims of the drivers. Set into the back panel are two pairs of multiway binding-post connectors joined by jumper straps. By removing the jumpers, you can operate the speaker in a biwired or biamplified configuration.
Mirage says that the M-790 speakers will sound best if placed 2 to 3 feet in front of the wall behind them and at least 2 feet from the side walls. For optimum bipolar performance, the wall behind them should be reflective, and the speakers may be toed in slightly to focus the center of the stereo image at the listening position. We tried to meet those conditions as closely as possible, although an ideal placement for these speakers was not feasible in our listening room.
Anechoic response measurements do not give an accurate picture of a speaker such as the M-790, whose sound depends heavily on the contribution of signals reflected from nearby walls. Our loudspeaker room-response measurements usually correlate well with perceived sound quality, however, and that proved to be the case with the M-790.
Its room response was among the flattest we have measured from a speaker, with less than +/- 2 dB overall variation from 400 Hz to 13 kHz. There was a slight peak (about 4 dB) at 17 kHz, falling to +2 dB at 20 kHz. Room-boundary effects were apparent below 400 Hz, though to a much lesser degree than with most speakers. In fact, the overall response from 20 Hz to 20 kHz (without smoothing or correction) was flat within +/-5 dB, a quite remarkable figure for a "live room" measurement.
The close-miked response from the woofer and its front port varied only about 6 dB overall from 36 to 500 Hz, with maximum output at 70 Hz. It spliced well to the room curve, yielding a +/- 5-dB variation from 20 Hz to 20 kHz, but it must be realized that the response below 500 Hz is inevitably affected by the room dimensions and acoustic treatment and is not exclusively a property of the speaker.
Horizontal dispersion was outstanding, with output at 45 degrees off-axis down less than 2 dB from the on-axis output up to 3 kHz and less than 4 dB all the way to 20 kHz. The smoothed response of the rear driver was within +/-2 dB from 800 Hz to 10 kHz, falling to - 8 dB at 500 Hz and 13 kHz. Its maximum output was between 4 and 6 kHz.
Minimum system impedance was about 5 ohms at 100 Hz. The curve also showed sharp peaks of 15 ohms at 16 Hz and 12.6 ohms at 52 Hz (from the reflex loading of the woofer) and a broader one of 11.3 ohms at 1.5 kHz. Overall, the speaker's 6-ohm rating seems realistic.
Sensitivity measured 84.5 dB sound-pressure level (SPL) at 1 meter with a 2.83-volt input, slightly lower than rated. When we drove the M-790 with a 5.3-volt signal, corresponding to a 90-dB-SPL output, the woofer distortion was between 0.5 and 1 percent from 1 kHz down to 200 Hz, rising to 3 percent at 100 Hz and 10 percent at 35 Hz.
The M-790 had excellent power-handling ability. The woofer began to sound distorted at 100 Hz with a single-cycle burst input of 900 watts into its 5-ohm impedance at that frequency. At 1 kHz it took everything our amplifier could deliver (650 watts into 10.5 ohms) without significant distortion, and at 10 kHz the tweeter absorbed 800 watts at the amplifier's clipping point.
The Mirage M-790 sounded every bit as good as it measured. Its spectral balance was first-rate, with no suggestion of over- or under-emphasis in any part of the audio range. Spatially, it had an open, easy quality, with a seamless and natural full-depth sound-stage appearing across the end of the room. Its imaging, playing the Chesky JD37 test CD, was among the best we have heard.
But given the manufacturer's suggestions on placement and installation of the speakers, it is still possible that we were not obtaining the very best sound the M-790 is capable of. That is an unavoidable problem with almost every speaker we test (or with any you bring to your home), since it is often impractical to shift the position of a desk, bench, door, or window to achieve perhaps another small step toward sonic perfection. Indeed, one of the most desirable characteristics for a speaker to have, once a certain level of sound quality has been realized, is the ability to function satisfactorily, if not optimally, in a reasonable variety of circumstances.
The Mirage M-790 meets this standard very handily. Its spatial and sonic qualities were excellent, even under less than ideal conditions. Although it is certainly not invisible, it is attractive and unobtrusive, both visually and sonically. It delivers a caliber of sound that would do justice to a considerably costlier speaker. The M-790 is well worth hearing if you are looking for a close approach to "high-end" sound without the usual price penalty.
