Floor Loudspeaker Reviews

Magnepan founder Jim Winey could be considered the patriarch of planar loudspeakers. His innovative leadership of and commitment to the technology over the past 20 years have propelled Magnepan to a position of preeminence in the speaker business. You won't find any hybrids rolling off the production line at Magnepan's corporate headquarters in White Bear Lake, Minnesota. The entire Magnepan line is devoted strictly to planars that use ribbon tweeters and quasi-ribbon midranges and woofers—not a stray dynamic woofer in the lot!

Magnepan's status in the marketplace is supported by sound value for the dollar. With models ranging from the affordable SMGc ($690/pair) to the popular MG-3.5 ($3150/pair) and the new and exciting MG-2.7 ($1995/pair), it's evident that good planar sound doesn't have to cost you an arm and a leg. Even the top-of-the-line MG-20 retails for under $10k/pair. In this day of $5k minimonitors, that's genuine value.

Why are they so BIG?
At 79" high and 29" wide, this question is exactly the sort of comment the MG-20s are likely to elicit from your non-audiophile spouse. Note that I've avoided the term Wife Acceptance Factor (WAF), as I find it extremely patronizing. It presumes that the wife's sole criterion in judging a loudspeaker is equivalent to interior decorating. I've known couples who have willingly accepted a baby grand piano into the confines of an already crowded living room—their love for music overcame other practical considerations.

The proper response is that planar speakers have to be so big for the same reason a piano has to be as big as it is: No one in his or her right mind would accept a piano the size of a violin. For the same reason, no one should take a planar the size of a toy piano seriously.

Whether it is to produce or reproduce bass frequencies, bigger is better. Efficient coupling to the impedance of air demands a large radiating area. A piano string cuts through the air with little acoustic-energy transfer—most of the acoustic power emanates from the piano's body and soundboard. Similarly, a 15" woofer is inherently more efficient than an 8" woofer in the deep bass, precisely because of its greater area—it's able to couple mechanical energy more efficiently to air. In the same way, a planar speaker's power finds full expression when it's allowed to assume realistic proportions.

Technical details
The MG-20 is a three-way design with a built-in passive crossover for the tweeter/midrange interface, and the optional XO-20 external passive network ($695/pair) for the midrange/woofer interface. Introduced in 1994, the XO-20 allows either single-amp operation or bi-amping without an active crossover. Previously, the MG-20 could only be bi-amped, with the help of two stereo amps and an electronic crossover.

Like all planars, the MG-20 combines a low-mass diaphragm with drive that's arranged to be uniform over its radiating area. All things being equal, low mass confers the advantage of high acceleration. The ability to start and stop quickly, relatively unhampered by inertia, translates into excellent transient response—the diaphragm is able to faithfully execute the requirements of the drive signal. The major advantage of uniform drive, or force-over-area, is the resultant excellent acoustic phase coherence; the wave launch of the drive-units is from a common plane.

The tweeter is a patented ribbon design driven directly without transformer coupling. A 0.3" by 60" by 2.5µ-thick aluminum ribbon is suspended in the magnetic field of two long, permanent bar magnets. This long, narrow ribbon provides excellent dispersion in the horizontal plane, and acts as a line source in the vertical plane. (By this I mean that the diaphragm is sufficiently tall compared with the height of the room that the interaction between the diaphragm and the floor and ceiling results in a cylindrical wavefront.) The ribbon has a very low moving mass, so take special care in handling. For example, never attempt to use a vacuum to clean the tweeter channel—you'll suck the life right out of it. For shipping, the ribbon is protected by a cover.

The midrange and bass drivers are traditional Magneplanar drive-units. The midrange driver uses a large but very thin—13&181;;—Mylar diaphragm to which are bonded rows of long conductive strips. The 137in² diaphragm is suspended in front of vertical rows of bar magnets so that the strips are centered in the magnets' fringe field. The similarly constructed 786in² bass driver uses aluminum wires instead of the strips. In all cases, it's the interaction of the current flowing through the ribbons or wires with the magnetic field of the bar magnets that provides the impulse force for the ribbon and diaphragms.

Preliminaries
Setting up a planar is no more difficult than setting up a conventional loudspeaker—provided one has control over the listening environment. As with any dipole radiator, it's imperative to allow adequate "breathing room" behind the speaker—at least 36" from the rear wall is a good starting point. Some absorption and diffusion behind the speaker are appropriate to partly attenuate and disperse the backwave.

Listening distance is another critical parameter. Slowly move the listening seat on the central axis until you settle on a suitable tonal balance. For me, that distance was 9', with the panels toed-in toward the listening seat. I also experimented with the position of the tweeter ribbons. Because the ribbons are mirror-imaged on the left and right front baffles, it's possible to position the MG-20s so that the tweeters are either on the outside or inside edges of the speakers. The inside position worked best for me, in that it yielded the most cohesive soundstage.

When all was said and done, the MG-20s ended up in roughly the same location as the Sound-Lab A-1s, but with the listening seat a couple of feet closer. The MG-20s' resultant soundstage, however, was quite a bit more spectacular than the Sound-Labs'. The A-1's greater radiation angle produces more side-wall reflections (at least in a moderately sized room), and hence a less convincing panoramic view. In contrast, the Magneplanars flooded the front third of my room with a seamless soundstage in which I was able to turn my head from left to right without missing a beat. In audiophile jargon, the speakers seemed to disappear, leaving in their place a living, breathing spatial framework.

Image outlines were remarkably life-sized—in the best tradition of planar speakers. Listening to a closely miked double-bass or piano proved a humbling experience. Rather than looking out at a parcel of space that even a child could wrap its arms around, the breadth and height perspectives projected by the MG-20s were totally believable.

Speaker cable of choice was TARA Labs Rectangular Solid Core Master Generation 2. As TARA Labs' Matthew Bond provided me with 18" sections of cable terminated with pin connectors, I was also able to cover the signal path from the passive network to the speaker inputs with RSC Master cable. For greatest soundstage transparency, I settled on a bi-wire configuration between the amp and the external passive network. Most of my listening was conducted with Acrotec's fabulous 8-Nines Stress-Free interconnects, whose praise I shall sing at a later date. And as for amplifiers—read on!

Sound: single-amping
My samples of the MG-20s were delivered with the external passive network, so that's how I initially deployed the speakers. Only much later did I turn to bi-amping.

My first order of business was to investigate the speaker/amplifier interface. After auditioning both the Air Tight ATM-3 and the Manley 175 tube monoblocks, it became clear that I would have to investigate solid-state amplification. Although both the Air Tights and the Manleys painted a warm and palpably exciting soundstage—lovely stuff—they failed to deliver satisfactory performance in two areas. First, dynamic headroom was constrained—the Air Tight more so, but even the Manley labored when navigating very loud passages. Second, there was a lack of punch and crunch through the lower registers, a loss of bass definition and transient power that robbed the music of impact and drama.

The MG-20 is a true 4 ohm nominal load, maintaining a 4 ohm minimum into the deep bass, and only falling to about 3 ohms in the treble. On this basis, it qualifies as a moderately difficult load. Together with a low sensitivity specification, this suggests the advisability of transistor drive. It was still surprising to discover that only solid-state amps capable of swinging several hundred watts into 4 ohms seemed capable of satisfying the MG-20's appetite for current.

The Classé M-700 solid-state monoblocks that I reviewed last month may not be alone in their ability to dish out a kilowatt into 4 ohms, but no other high-powered amp I've heard to date can do so as smoothly and as musically. The Classé excelled at both ends of the spectrum, dealing with tasks that could be broadly characterized as brawn and finesse. Bass punch and definition were exemplary, the M-700 fleshing out the MG-20's full potential in this regard. On the other hand, the manner in which the Classé caressed the bloom of harmonic textures earned it the respect of even Toob Man himself.

The Bryston 7B monoblocks proved another synergistic coupling. In fact, my first serious listen to the MG-20s was at Peter McGrath's (Mr. Sound Components) Miami home, where they were tri-amped with a stack of Bryston 7Bs. (Snell THX subwoofers were used on the bottom.) Program material at the time was Peter's own master tapes feeding an Audio Research LS5 line preamp. I still can recall the astonishing clarity and transparency of that particular setup; yet, even with a single pair of 7Bs, I was treated to a command performance. Although not as texturally smooth as the Classé, the 7B's main attraction was its remarkable level of midrange clarity and transparency.