Apogee Duetta II loudspeaker

Alvin Gold & Various, March, 1986

What I wanted to talk about briefly this month is the new Apogee Duetta, the baby of this speaker family. This particular baby will cost you the rather grown-up figure of $2300/pair; over here in the UK it costs a demonic £3300/pair, roughly double.

We got off to a bad start with the Duettas. Ricardo Franassovici, of UK importer Absolute Sounds, thoughtfully decided to help me unpack and set them up, but on doing so discovered that the screws for mounting the rear of the baseplate were missing. impatient to hear what they sounded like, he stood them up on their vestigial fixed stands, and the inevitable happened: one of them keeled over, taking a bite out of a windowsill and doing some internal damage to the frame of the speaker in the process. They nevertheless continued to work.

That was the only snag, however, and the Duettas have subsequently proceeded to charm everyone who's heard them, with the single exception of the Man Who Doesn't Like Loudspeakers (Keith Howard, editor of Hi-Fi Answers).

I think I understand why he doesn't like them, but it does nothing to diminish my admiration for a loudspeaker which, how ever uncomfortable it can feel at times, is the single most extraordinarily lucid and colorful transducer I have ever heard, with the possible exception of the Koetsu Rosewood Signature (which also has a telephone number instead of a price tag).

The bass end, despite being slightly OTT, has real depth and power combined with pitch, bounce, and an unmistakably tactile quality. Bass instruments have an unbounded, in-the-room quality that for once makes sense of that old cliche about reaching out and touching the instrument. At times, that's almost exactly how it was. The speaker has near-perfect integration and uniformity from the lowest to the highest notes, and a wonderfully vivid sense of tonal color and instrumental separation.

But they stretched my Krell KSA-50 up to and frequently beyond its limits. It took an all-too-brief spell with a new KSA-100 (and a prototype 300-watt class-A monster from Musical Fidelity I'll tell you more about in the future) to show that it was the amplifier, not the loudspeakers, putting the lid on that final 10%.

All this makes the Duetta a very expensive animal in more senses than one. Right now, though, it is my sincere desire to be marooned on a desert island with a pair of these for company (footnote 1).—Alvin Gold

---

Footnote 1: Though I have no desire to be marooned on a desert island, I have to concur in AG's assessment of the potential wonders of the Duetta. I was privileged to hear an a recent demonstration of them at Audio Vision in Arlington, MA. The problems that J. Gordon Holt and I heard at Apogee's CES room in the summer of 1985 were totally absent, and the remarkable coherence that I've heard from every Apogee speaker was quite stunning. I can't say whether they'll pass JGH's "raise the hackles" test, but most listeners will find them wonderful to listen to—but only with absolutely the best source material and drive electronics.—Larry Archibald

Anthony H. Cordesman reviewed the Duetta in September 1986 (Vol.9 No.7):

I normally like to listen for several weeks before commenting on a new product, particularly one that I feel breaks as much new ground as the Apogee Duetta II. Anyone who remembers the one time High Fidelity ever heard an audio product that sounded truly different, and praised it as such, will probably remember that the product the magazine praised as redefining the state of the art was the Bose 901. At the same time, the Duetta II breaks so much new ground, and is so obviously a superb speaker system, that it simply would not be fair to you readers to put off reporting on this speaker until the next issue.

In fact, my wife's reaction to the Duetta II may be worth a thousand of my words. I had just unpacked the Apogee Duetta Series II, and set it up in the manufacturer's recommended position. I hadn't gotten around to really listening yet, and was still checking the speaker position and wiring as the Duetta IIs played, but my wife was sitting in the listening area. I thought she could tell me whether the channels were balanced, and asked her what the speakers sounded like.

The response I got was a great deal more dramatic than a comment on whether the channels were balanced. An exact quote: "They are the first speakers I've ever heard that remove the veil from the music that always tells you that you are listening to a hi-fi system." Well, my wife has heard virtually every high-end speaker that I've heard, including the Apogee Scintillas, the Quad ESL-63s, and the Infinity RS-1Bs that I have used as reference speakers. She is not given to ready praise. In fact, she is apt to sulk for several days after every major disruption of her living room, and be extremely critical of any speaker simply because it is new.

As a result, I immediately stopped tweaking and started listening. It was worth it! I suspect it may be weeks before I find the right room placement, amplifier, and speaker cable to get the best out of this speaker. I am already sure, however, that I have never heard more detail and information in a more musically natural form. It may be years before Apogee fully explores the limits of ribbon speaker technology, but the Duetta II is a superb product, and redefines the state of the art in many important respects.

Design Evolution in the Duetta II
Let's take a few minutes before I describe the sound, however, and go over the design evolution of the Duetta II. As you have already read in these pages, the original Duetta built on the technology of the large Apogee and Scintilla, and provided a more affordable all-ribbon speaker, one that many good amplifiers could drive.

The Caliper showed, however, that Apogee could do much more to produce a musically realistic sound, and at a much lower price. Further, Apogee made progress in a research program on canted ribbon transducers which could act as both midrange and tweeter. This progress showed that such a ribbon could provide excellent horizontal dispersion and realistic vertical imaging in a comparatively short length. Apogee also developed proprietary new approaches to ribbon suspension and mechanical acoustic shaping, which improved the smoothness of the sound of the combined midrange and tweeter (MRT) ribbon. As a result, it found that the use of a single ribbon eliminated potential time-alignment problems inherent in the use of separate midrange and tweeter ribbons.

The Duetta Series II speaker draws on other improved ribbon speaker design techniques which Apogee developed in designing and manufacturing the Caliper. For example, Apogee uses multi-sloping crossover shaping with a 6dB/octave slope at the crossover frequency, and uses a rear panel switch to add a gentle 2dB rolloff at the high end of the MRT to adjust tonal balance to different rooms and source material.

The Duetta Series II also incorporates a provision for an active crossover in the biamped mode. Apogee says that the use of this crossover improves resolution and tonal balance adjustment, gives you 3dB more headroom, and provides superior woofer and midrange shaping. I have not yet had a chance to use this unit, but will report on it when I give you my final thoughts on the sound of the Duetta IIs in the next issue.

Redefining Transparency
I must again stress that proper listening to speakers takes weeks—not days—of experimentation. Accordingly, you should use my comments as a comparative reference for your own listening, and not as revealed truth. (Does any one ever pay that much attention to an audio critic?) Nevertheless, my reactions after a week of intensive listening are:

Deep Bass: Not present in the same strength and power as the larger Apogee and Infinity speakers, but very much there nonetheless. The best cone subwoofer systems are still superior in this area, but only with exact placement and superb active crossover designs and drive amplifiers. Coupled to the extraordinary flatness of the mid and upper bass, the feeling of deep bass power is far more satisfying than in any competing dipole, including the highest-priced electrostatics and Magnepans.

The bass characteristics of the Duetta II may well allow it to outperform the Scintilla and larger Apogee in most real-world listening rooms, and allow you to keep the room interaction, inevitable with dipole speaker designs, under exceptional control. This makes the Duetta II comparatively easy to place, provided that you obey the manufacturer's instructions and keep it 3-4' from the rear wall. Closer placement may also work quite well, but will almost inevitably reinforce some part of the deep bass at the cost of reducing other bass.

Mid and Upper Bass: The mid and upper bass are exceptionally flat. There is none of the slight emphasis or "warmth peak" found in the bass of the Caliper, and little of the room-interaction masking common in the larger Apogees—and any other large dipole speaker—when they are operated in reasonably sized listening rooms. There is exceptional detail in the mid and upper bass. As a former drummer, I could recognize more accurate percussion information in the mid and upper bass than with any other speaker I have heard. Only a really well set-up Quad ESL-63 system can compete with the Duetta IIs in this area, and that has trouble with the lower midbass.

Upper Bass/Lower Midrange: The exceptional, state-of-the-art, transparency that emerges in the mid and upper bass is sustained into the critical upper bass/lower midrange transition area. As a result, you may hear more from your records and CDs than you have ever heard before. The only uncertainty I can think of is that the match between the bass ribbon and combined midrange and tweeter seems to be equipment-dependent. Getting the best possible performance requires experimenting with different amplifiers, speaker cables, and room placement.

Even without such efforts, however, the upper bass/lower midrange transition area will still be very convincing, and few speakers ever made will give you a more realistic hall effect. I suspect that the use of the active crossover will also allow you to go one step further, and shift the overall spectral balance to give a more forward sound.

Mid-Midrange: This is the most critical area in reproducing music, and one where the Apogee Duetta IIs redefine the state of the art. Extended listening leads to a constant series of new discoveries of what is actually in recordings, without any surprises or unnatural emphasis. This detail is common to all Apogees, but the Duetta IIs are far more convincing than any previous Apogee I have heard—or any other speaker, for that matter. The Quad ESL-63, which has always been my reference standard in this area, has just been displaced by the Apogee Duetta II.

Upper Midrange: If the prototypes of the first version of the Duettas were a bit bright in this area, the present Duettas are so smooth that it is going to take you several hours to get over the shock of not hearing your usual speaker colorations. I found the Duetta IIs to be very listenable with virtually all material, even with their MRTs set flat (though I actually preferred the -2dB switch setting). Again, the level of resolution surpassed that of any speaker I have heard to date. If you rely heavily on CD, you simply must hear the Duetta IIs. No speaker has yet been able to get as much natural musical pleasure out of the better CDs, and, while you won't rush out to sell your record collection, this speaker also redefines the musical pleasure that CDs c an provide.

Upper Octaves: There is a mix of smoothness, well-chosen radiation characteristics, and transparent detail in this region that simply has to be heard to be believed. A real-time measurement with a one-third octave analyzer confirmed that the highs are very smooth and flat, and go on forever—or at least well above 20kHz. It's amazing how musical the highs can sound and still be there in full abundance.

Depth: Depth is excellent at normal listening levels, but be careful. The transparency of the Apogees, like that of the Quad ESL-63s and a few competing speakers, encourages you to listen at too high a level. This can collapse depth and give a feeling of loss of detail in dynamic peaks. Watch your listening levels. Play them loud, but by all means keep them natural.

Soundstage Width and Height: Speaker placement gives you so much control of width, without a hole-in-the-middle effect, that you can virtually create a soundstage to taste. The only speakers I have heard that are more realistic are the Infinity IRS and RS-1b II.

Imaging: A superb arc of instruments, with excellent placement in depth as well as from left to right.

Dynamics and Transient Handling: The speed of dynamic changes and the ability to handle soft, moderate, and loud transients is rivaled—if at all—only by the larger Infinity and VMPS reference monitors, although the Infinities and VMPSs can handle loudness levels above the 106dB level of the Duetta IIs. The practical result is a speaker that can play very, very loud, do so better than any electrostatic or Magnepan I have heard, and do so better than virtually all cone speakers.

You can drive the Duetta IIs to levels that compete with most other speakers, with just about any good power amplifier that puts out 100 watts per channel. While you can biamp, I strongly preferred using one stereo amp, and biwiring, to biamping without an active crossover. I wouldn't rush out to buy two amps, given the coherence and excellent power handling capability you can get with any good stereo 100-watter.

I did notice listening room limitations at higher power levels. I was getting a bit too much reflected sound when I really cut loose, but this was relieved by better placement. I also found I got better results in this area of sonic performance when I switched speaker placement from 3.5 feet away from the rear of the long wall, to one-third the distance of the room from the rear wall. This produced an immediate major improvement in transparency at very loud listening levels, although at some cost to the size and depth of the soundstage. Since your room is certain to be different from mine, this indicates only that you should experiment.

As my wife said at the start, the Apogee Duetta IIs, more than any other speaker, remove an entire layer of coloration from the sound. They are at least a truly excellent speaker system; I strongly suspect that more extended listening will reveal they are the new state of the art.

There are a great many things I have to learn, however, before I can fully report on the overall spectral balance, room effects, and amplifier- and speaker-cable match. I hesitate to say that this is the most value for money I have yet encountered in a high-end speaker only because I have not had the time to search out any minor quirks; nor have I heard the Duetta IIs with their active crossover.

You also need to show a bit of sense before rushing out to buy a pair. Not everyone has a room in which they can place speakers 3 feet from the rear wall and give 2 feet clearance on the sides. You may still need a good cone speaker with no rear radiation, even if you can afford the Duetta IIs. I should also stress that we sometimes underestimate the level of progress and sophistication available at moderate prices from designers like Thiel, Vandersteen, and KEF.

I have heard so many dipole speakers work well in small rooms and badly in large ones, however, that I would not rule out using the Duetta IIs even in small rooms, after tuning their placement for the best compromise of room interactions. I'd just caution you to work closely with your dealer. No dipole speaker can easily be placed in a small listening room.

I suspect that the Duetta IIs will rapidly force competing speaker manufacturers to make whatever improvements they can in their existing line. I would not sleep easily were I making Magnepan, Quad, or Martin-Logan speakers—or even the larger Infinity Reference series. Yet these are all outstanding speaker manufacturers at the top of the high-end pyramid.

Apogee already seems to have forced Bob Carver to rip off Apogee's styling in order to compete. One wonders what manufacturers who do compete with Apogee will do to equal or surpass this new level of sound quality. The Duetta IIs are brutal competition, and I expect a sudden flood of new ribbon systems a year or two from now, as other manufacturers begin to catch up.—Anthony H. Cordesman

Martin Colloms gave a listen to the Duetta in January 1987 (Vol.10 No.1):

Panel speakers are back in fashion. After years of determined effort on the part of a few established manufacturers, the number of these designs has seen a marked increase, and many new exotic models have appeared. Stereophile has recently reviewed two leading examples of the genre, the $2780/pair Apogee Duetta and the $2490/pair Martin-Logan CLS, (both in Vol.9 No.7). To judge by the tone of letters arriving at the magazine's offices, the reviews generated heated controversy. John Atkinson asked me, therefore, to conduct an in-depth examination of the two models, to give a fuller picture of what these speakers are capable of.

Design Compromises
Although radically different in appearance, the Duetta and the CLS are both medium-sized, floor-standing, open-panel speakers. The Duetta is a two-way system, with a moderately sized, broad-band ribbon tweeter working through the upper mid and treble ranges. It is related to the three-way Scintilla, which uses a composite multiple-ribbon system for the mid and treble range.

The number of "ways" is crucial to a design, since no single transducer can properly encompass the breadth of the audible frequency range. From the design viewpoint, the more ways—ie, the greater the number of divisions of the frequency range—the more freedom there is for the engineer to trim and balance the frequency response to provide a natural sound. Conversely, with a low number of "ways," the designer has to fight for continuity and an even power over the range, not always with complete success. Increasing the "ways," however, makes it more difficult to design a well-integrated full-range system out of proportion to the increase in complexity.

Apogee has pioneered the use of modern "ribbon" technology, and In the case of the Duetta, this description is certainly true for the HF unit. Here, a tall, pleated aluminum foil/Kaptan ribbon with three conducting paths is suspended between the poles of a powerful, linear, open magnet. The radiation is bidirectional and bipolar, the energy behind being out of phase by 180 degrees with that for the front. Unless placed very close to a back wall, this will not result in specific cancellation, since by the time wall-reflected rear waves have combined with the direct radiation, their phase is randomly indeterminate. Suppose the panel is typically placed at five feet from the back wall, and the listener is 15 feet from the speaker. At the low frequency end of the range handled by the tweeter ribbon, say 1kHz, the listener is 15 wavelengths away from the front-panel sound, and 25 wavelengths from the reflected sound to the rear. Given normal room reflections, specific cancellations will be diffused and of small significance; with reducing frequency, however, this factor will assume increasing importance.

The lower frequency range of the Duetta is handled by a stretched film diaphragm, tensioned and supported over its whole boundary perimeter, and referred to by Apogee as a "ribbon." Its motion is akin to a drum skin, as is that of the Magneplanars and the vast majority of electrostatics. This is quite distinct from the piston-like, push-pull, action of a freely suspended ribbon whose fundamental to-and-fro resonance may be so low as to occur below audibility. At present, it is inconceivable that a loudspeaker could be made to operate fullrange in a true ribbon form. The magnet system would be so huge that no-one would be able to move it. It is also likely that such a design would overload prematurely at subsonic frequencies.

Apogee has overcome, in a number of ways, many of the fundamental resonance problems of a stretched diaphragm. The moving element of their woofer is a laminate combination of aluminum foil and Kaptan plastic tape with good self-damping properties. The element is generally pleated in the horizontal direction to increase its resistance to bending, while the shape is semi-trapezoidal to maximize its geometric asymmetry and thus disperse resonant modes. Finally, the upper and lower sections of the diaphragm are differentially tensioned to provide a broad, double-tuned low-frequency resonance, rather than one of a higher Q.

Several factors control the frequency response of an open panel. At low frequencies, the bass rolls off at 6dB/octave and is generally augmented by some deliberate diaphragm resonance. After passing through a fairly level region, the output begins to fall naturally and the drive signal must be crossed over to the next driver before this happens—in the case of the Duetta, around 500Hz. For the mid-treble ribbon element, the low-frequency rolloff begins at over 1kHz, and the crossover overlap is deliberately broad to help account for this. Once again, given some consideration of the acoustics of the vertical slot in which the tall ribbon tweeter operates, and the mild canting of the element to improve the vertical directionality, the treble ribbon's output falls at the top of its band. In the case of the Duetta, this is at frequencies above 12kHz. The Scintilla's more extended top-end response is assured by the final set of four half-inch ribbons, which augment the output from the mid-treble ribbon.

The Duetta's treble ribbon is a wide-range transducer, covering a range from some 500Hz to 22kHz, and is of exceptional sound quality. Advantages of this large ribbon include a virtual absence of resonance or coloration, with great acoustic transparency—no physical obstruction before or behind the driver element, plus direct coupling of the applied electro-mechanical force to the air. Good horizontal directivity is achieved by the virtual line source form. However, owing to the wide magnet gap which is necessary to accommodate the conductor, the tweeter does not offer much sensitivity. Running the three conductor elements of the ribbon in series brings the load impedance to 4 ohms, but the sensitivity remains very low, in speaker terms, at typically 78dB/W (this is an 8-ohm watt), which is some 10dB below the average. There are penalties to pay for this low sensitivity in terms of required amplifier power.

The Duetta's low-frequency driver is necessarily subject to some resonance modes and, in addition, suffers from some acoustic obstruction due to the perforated steel-plate baffle used to support the massive array of planar magnets. These provide the distributed magnetic field associated with the zigzag current flow of the diaphragm conductor pattern. The acoustic "window area" of the bass section is not very high, though if this were increased, panel rigidity would suffer. The bass driver, having a one-sided magnetic field, is driven in single-ended rather than the preferred push-pull mode. In theory, this would predict higher distortion levels, but in practice, the distortion from such a large radiating area is quite negligible, even at realistically high sound-pressure levels.

Due to their large area, the Duetta diaphragms radiate heat well, providing a high power handling which is necessary in view of the low sensitivity. A particular feature of the Apogee drive system is its very high inherent linearity, resulting in a freedom from the compression effects apparent in many moving-coil systems, as well as in some electrostatics when the peak handling limits are exceeded.

Sound Quality
I shall leave the more effusively indulgent characteristics of sound quality to my American colleagues and present (I hope!) a rather more academically objective view.

This speaker has improved considerably since my first acquaintance with the original samples some 15 months ago, which I declined to review. In my system, problems were experienced with tonal imbalance, midrange glare, and a lack of precision in the high treble, though other critics seem to have enjoyed greater success with its sound.

With the Mk.II, I found a greatly improved uniformity of frequency response, and the high-treble problem was avoided. The speaker was easy and relaxing to live with, and had great virtues. However, there was also what I feel to be a considerable flaw: the Duetta was demonstrably and unarguably rich in balance, and sounded dim when set against my established references, all of which have been directly compared with live sound sources under controlled conditions. If the Duetta is the only speaker you use, or perhaps the only speaker used that day, and you only play your brightest-sounding records, then you may become accustomed to its tonal balance. In my 80m³ room, the bass was almost overpowering in level, while the balance sounded as if downtilted with increasing frequency all the way from 50Hz to 10kHz. (Imagine a Quad 34 or 44 tilt control rotated fully for the richest tonal balance.) I felt a strong urge to beg, steal, or borrow the nearest Cello Palette and attempt some moderation of this speaker's slow, ponderous balance.

In addition, while the problem I had perceived above 12kHz from the Mk.I had gone, so, it appeared, had the extreme treble itself! The treble sounded filtered, with little air or sparkle in the final audio octave. The end result was still very sweet, but lacked a sufficiently "open" quality. Perhaps surprisingly, however, the Duetta sounded best with the treble switch up (ie, dimmer). With the switch set down, the treble was lifted slightly at the expense of a mild return of upper-mid "glare," something I can do without. I also indulged in some strictly illegal fiddling: I tried placing 1.5-ohm resistors (25 watt wirewound) in series with the woofer panels, which helped the tonal balance somewhat.

The Duettas are amazingly insensitive; for example, Audio Research M100s (on their 4-ohm taps) sounded wonderful at low levels, but failed to stir the Duetta into life at high levels. Substitution of Krell KMA-100s (lovely amplifiers these, despite their being solid-state) essentially maintained the standard of reproduction but added some 6dB of level, bringing the Duettas to a satisfactory volume level.

A quick lab check showed that the KMA-100 could churn out 200 watts into 8 ohms, and 360W into 4, yet to obtain the full dynamic range I believe the Duetta capable of, I felt the need for a KMA-200 or the equivalent. In room, this would establish maximum sound levels of typically 105dBA from a stereo pair. For reference, a KEF R107 fed a standard 100W (8 ohms) per channel will deliver 107dBA. An MGIIIa fed its power limit of 100W (8 ohms) would deliver a satisfactory 101dBA.

With its rich balance, the Duetta needed heavy driving to bring up the mid and treble ranges subjectively, whereupon the magic qualities of this fundamentally musical transducer were then revealed. Most of the frequency range was of high purity with excellent transparency, and once you had become adapted to this speaker tonally, it rewarded you with an excellent focus, fine orchestral perspectives, and big soundstages. The usable treble range was dulled, but otherwise of very fine quality. Leaving aside the question of balance, the bass was exceptionally good, appearing powerful, clean, articulate, and extended, virtually to the subwoofer level (footnote 1). But most importantly, the midrange was very good indeed, and worthy of both the brandname and the asking price.

Coloration (in the resonance sense) was very low, the sound imbued with a great sense of ease. The Duettas were not immediately lively, in a dynamic sense, but did continue to impress with their high resolution of inner detail, as well as by their discrimination of subtle harmonic shadings.

Conclusion
Given a near-unlimited amplifier budget, my ultimate sympathies lie with the Duetta II. As a reviewer, however, I could not cope with it in its present state. It is simply too rich, tonally, too insensitive to use as a reviewing tool; if intended as the basis for a music room . . . well, that would be another matter! If the diminished final octave does not matter too much, and if really high sound levels are not required, and if a large room is also available (quite a few "ifs"!), then the Duetta is the best choice. There is no doubt that its intrinsic quality was in the highest class, and implied no limit in terms of the matching amplifier quality; the Audio Research M100 proved this, though it didn't achieve a sensible volume level.

I would ask Apogee to consider an approved modification for bypassing the crossover. Krell's Dan D'Agostino could then work up a nice equalized electronic crossover, working in conjunction with a pair of KSA-100s, to provide direct-coupled, biamped operation. I confidently predict that this combination would provide one of the finest performances for the money presently available in the business (footnote 2).

I have outlined the major characteristics of these speakers; now it's up to you!—Martin Colloms

---

Footnote 1: In larger rooms—200m³—the bass was proportionately reduced, and much better balanced.—Martin Colloms

Footnote 2: Provisions have been made for the Duetta Series II to be driven via an active crossover. Owners should consult the Manual for instructions.—John Atkinson

George Graves wrote about the Apogee Duetta II in May 1988 (Vol.11 No.5):

Even though Apogee Acoustics' Duetta II, a full-range ribbon loudspeaker, has been reviewed a couple of times already in these pages (by Martin Colloms in Vol.10 No.1, by Tony Cordesman in Vol.9 No.7), their findings do not tell the whole story of the Duettas' sound in my opinion. In my efforts to elicit the very best from these loudspeakers, I've found them so cable-sensitive that one's opinion of how Duettas sound will depend to a very great extent upon what cables were used and whether or not the speakers were bi-wired.

The Apogee Duetta IIs are the most cable-sensitive speakers I have ever encountered. With Magneplanars, my regular speakers, cables make very little difference. The good ones may improve the character of the top end a smidgen, or slightly deepen or widen the soundstage, but these changes are, at most, subtle. With Duettas, however, in spite of the relatively easy, mostly resistive load it presents to the amplifier and speaker cables, the type of cable used will make or break this speaker system.

Apogee supplies shorting bars to strap the separate inputs for woofer and tweeter together, but recommends bi-wiring, whereby two sets of speaker cables are run back to the amplifier. They mean it! Conventional wiring results in a poorly defined sound with very little soundstage that, in view of their not inconsiderable cost, is very disappointing. Bi-wiring should be regarded as mandatory.

When I first received my Duettas, I had on hand only a pair each of Monster Cable Powerline II and FMS Gray cables. Since the Powerline was of a heavier gauge than the Gray, I naturally put it on the woofer, and connected the Gray to the midrange/tweeter ribbon. The result was terrible: The speakers had an unpleasantly honky, forward midrange. I was about to give up (being used to the unfussy Maggies, it never occurred to me that the cables could be at fault), so I called a friend who was an Apogee dealer. Upon hearing of my plight and listening to my explanation of my set-up, he made one suggestion: "Swap the cables." No, that couldn't be it. Cables never have that much effect on speakers. Out of desperation, I tried it. Whaddya know? Putting the FMS Gray on the bottom and moving the Powerline II to the top fixed the problem. Suddenly the speakers were fairly well-balanced in frequency response, except for a slight tubbiness in the midbass (about which more later) and a slight darkening of the top. The midrange glare was gone.

A couple weeks later, Monster supplied me with a set of their new top-of-the-line M1 speaker cables. I was able to replace the FMS and the Powerline II with these, and the quality of the sound changed again! This time the entire upper two octaves darkened considerably. At the same time, the soundstage grew wider and deeper, and imaging improved. The bass became tighter and better focused, with much-improved transient response. A mixed bag. I liked everything except the high-end darkening (the Powerline II did enough of that already). I finally found a good compromise by using the M1 on the woofer (which crosses over at about 500Hz) and going back to the Powerline II for the tweeter. But I still wasn't happy with the sound. If the Duettas had been lesser speakers, I would have just given up. But they kept promising more than I was able to elicit from them, and this drove me to keep trying.

I spoke with Jason Bloom, of Apogee, on the phone and told him of my cable saga. He agreed that the speakers were indeed picky, and suggested that a Swiss cable, the Symo, that he'd used on the more expensive Diva model might just do the trick on the Duettas. He then shipped me two pairs of sufficient length to use with my system. The Symo cable (retailing Stateside for about $15 a foot) is unprepossessing indeed. At first glance it looked a lot like Monster Cable's cheap Superflex. A closer examination, however, showed that this similarity is superficial. Both cables look like pinkish-clear 300 ohm TV twinlead that has contracted elephantiasis. But there the similarity ends; where the Monster consists of two loosely braided bundles of copper strands per conductor, the Symo has a single bundle of copper strands wound so tightly around a solid core that the windings appear almost perpendicular to the cable. The solid core also makes the Symo stiff.

Replacing the Monster M1/Powerline II combo with Symo changed the sound of the Duettas drastically: The top end was now open and fast, the highs sparkled, and triangles floated over the rest of the ensemble. The brasses had more bite, and the bass was tighter and better defined than ever before. All instruments had more air around them, and the imaging was the best so far. This change was overwhelming; it took me several more days of listening before I was ready to make any recommendations.

Recommendations: If you can afford it (and if you can get it—this stuff is hard to come by), I suggest you have your Apogee dealer sell you a full set of Symo. This will add about $600 (for four 10' lengths) to the overall cost, but will save you a lot in the long run. At today's speaker-cable prices, you can easily spend twice that just searching for the right cable. If you can't swing the Symo right away, then I would opt for the Powerline II by Monster. It's cheap (about $2.50 per foot) and degrades the performance of these speakers much less than do most other cables. The difference between Powerline II and the Symo is much less than between single wire and bi-wiring, so whichever cable you buy, buy four runs.

One of the more curious aspects of the Duetta II design is that Apogee provides no way of bypassing the speaker's built-in crossover. So even though there are separate sets of terminals for the woofer and tweeter on both speakers, it is impossible to actually bi-amp them. The Apogee instruction book does show how to use double amplifiers with a separate amp for the woofer and tweeter, but these amps are both fed a full-range signal from the pre-amp without the use of a low-level crossover. I can see no real advantage to this scheme except in the case when one's amplifier size is marginal.

Though the Duettas are less of a problem to drive than some of the older Apogee models, they still require gobs of current. Apogee recommends a minimum of 100Wpc, but after living with them for a while, I recommend at least double that. It's not the power that the speakers need so much as it is the current. Amplifiers get their power ratings by figuring the power using the output device's voltage swing across the load (usually 4 or 8 ohms), expressed as Power (P)=Voltage (V) squared, divided by the load Resistance (R). It should be obvious that an amplifier's power supply must be able to supply enough current for the voltage to swing high enough to develop its power rating across the load, but often, due to cost restraints in a very competitive market, a power supply will be designed to do this with little or no reserve. When the impedance drops below 4 ohms or so, the power supply just cannot provide enough current, and the DC voltage available across the output devices drops. In this case, a current-hungry speaker like the Duetta should be given plenty of watts in order to be assured of enough current.

When you try to drive these speakers with less than about 200Wpc, they suffer in dynamic contrast. It might be advisable (for cost reasons if no other) to purchase a duplicate of one's current amp and double-up by using one channel of each amp to drive the woofer, and the other channel to drive the tweeter. This will divide the load evenly between the two available channels, thus reducing the power requirements on each. By dedicating one entire stereo amp to each speaker, you will end up with the advantages of a "dual-mono" amplifying set-up as well.

The sound: First of all, the most striking aspect of the Duetta sound, and the one that first assaults the sonic senses, is the bass. It is, in a word, unbelievable. In my main listening room, the -3dB point seems to be about 25Hz. The bass is not only plentiful, but is tight and quick to boot. Organ music is visceral in a way that I would have thought impossible from bipolar speakers.

In large measure, the manner in which a bipolar speaker couples to the room determines the ultimate low-frequency performance which can be expected. As stated earlier, the Duettas like to have lots of room around them. When I first set up my pair, I placed them the same distance from the back wall as I had placed the Magneplanar Tympani 3Cs which preceded them. The low end was impressive enough, but the midbass between about 80Hz and 120Hz exhibited a slight, broad peak, which, although it did not give the feared "one-note-bass" effect, was nonetheless unpleasant. I found that in my listening environment, it was necessary to move the Duettas out to about 40" from the rear wall to totally remove this midbass hump. This experience, of course, merely reinforces the fact that bipolar speaker placement is largely a matter of experimentation, and what works or doesn't work in my listening room has little to do with what might work in yours. I can promise you bass extension rarely heard in audiophile speakers these days, and I can tell you that the quality of that bass can be startling.

The midrange in the Duettas is also excellent. After fixing the aforementioned cable problem, the midrange glare was replaced by a finely balanced midrange which has the rather unusual ability to really belt when called upon to do so. If you've ever been in a room where live brass are playing, you have probably noted how really "brassy" they sound. The sound just sort of blats at you in a rather loud and raucous manner, and is anything but polite. Very few speakers can capture this blast of wind and make the listener sit up and take notice. The Apogees do this very well. They also have the ability to separate instruments and delineate dense orchestral textures. It seems that no matter how loud and complex proceedings become, the speaker never loses composure, and things never become thick and congested.

The high frequencies are, of course, the range of the Duettas most affected by cable differences. With the Symo cable the highs are flat (with the tweeter switch in the up position) and well-extended. (Measuring nearfield frequency response with a calibrated microphone coupled to a Hewlett-Packard model 400 audio voltmeter and a swept frequency source, I was unable to correlate MC's rolled-off highs in Vol.10 No.1, finding the -3dB point to be at 18kHz (MC measured -3dB at 12kHz). Jason Bloom explained that this was due to the fact that these speakers have been improved considerably since MC reviewed them, and in fact not only have much improved highs, but are 5dB more efficient across the board as well!)

The most impressive characteristics of this speaker's top end are the speed and the utter lack of coloration. The high-frequency detail is astounding. The tweeter ribbon's ability to recreate the resinous quality of properly miked strings gives me goosebumps, and triangle and bells have the proper attack and decay (very difficult for most speakers; the only other speakers I know of which have this quality are the ribbon-tweetered Magneplanars and some electrostatics). Very impressive.

Conclusion: Apogee Duettas are capable of near-state-of-the-art performance, but are so sensitive to cables that without the right ones, you won't get the performance you paid for. They are also amplifier-sensitive. To sound their very best they need a good power amp with lots of current-sourcing capability. If in doubt, don't buy these speakers without first hearing them with your own amplifier. My experience with dipole radiators is that even though they are room-placement-sensitive, it is a rare room indeed where there isn't a place where they will sound satisfactory. Be prepared to experiment.—George Graves

Sidebar 1: Measurements

Just how hard is the Duetta to drive? Contrary to rumor, it proved quite tolerable—no less than 5 ohms, almost purely resistive, on the "1" setting, and it would warrant an across-the-board specification of 6.4 ohms, which is an easy load in speaker terms. The amplifier problems arose, not from an excessively low impedance as in the case of the 1-ohm Scintilla, but from its chronic insensitivity (in normal speaker terms) of about 80dB/W. The impedance graph (fig.1) reveals the crossover located at around 500Hz.

Fig.1 Apogee Duetta, impedance magnitude.

Measuring the sound output in 1/3-octave bands, the mid-tweeter response, shown on fig.2, is pretty healthy down to 400Hz. The vertical marker is placed at 12.5kHz, and graphically demonstrates the declining final octave, even when measured directly on-axis, with the mic on the "hottest" angle. Down 3dB at 12kHz, it was -10dB by the 20kHz 1/3-octave band. This graph also shows the output of the bass driver and its excessive level when interfaced with the tweeter, typically 6-8dB too high. (Note that this curve will encompass some significant nearfield effects, particularly in the bass.)

Fig.2 Apogee Duetta, acoustic crossover.

Fig.3 is a composite of the axial response, plus the output at 10 degrees above axis, and 30 degrees off the horizontal axis (toward the center stage). This shows that the output off-axis is pretty well maintained in the desired manner. At 30 degrees to the horizontal, the 12kHz region picked up a little but with no significant improvement in extension. On driver integration alone, the Duetta can be rated fine.

Fig.3 Apogee Duetta, response on listening axis, at 10 degrees above axis, and 30 degrees horizontally off-axis

Finally, we come to the computer-averaged response assessed in the listening space (fig.4), a summation of some 64 responses. In my 80m$s3 room, the 30Hz and 25Hz bands were clearly excessive in level, with the 30Hz rising 12dB above the computed median. Note that the bass rise was part of a rising curve and not an isolated "boom." From the response, it is clear that the general energy trend is rather rich, with the midrange broadly weighted to a maximum in the 400Hz to 1kHz sector (the marker is at 1kHz). Above 1kHz, the output declined some 5dB, though in a fairly controlled manner. The average output held up to 10kHz with a desirably smooth rolloff thereafter. The dotted curve shows the effect of the 1.5 ohm bass resistor—a mild improvement in balance.

Fig.4 Apogee Duetta, spatially averaged response in MC's listening room.

Larger rooms would definitely improve the Duetta's bass-mid balance, though the low bass would remain overpowerful down to 30Hz. For the benefit of those readers not familiar with these room-averaged responses, I can assure you that it is possible to obtain a room curve using this method which runs within ±3dB 25Hz to 200Hz, ±2dB 200Hz to 8kHz, with a gentle rolloff thereafter. (This latter effect is due to the finite directivity of almost all commercial tweeters at higher frequencies.) Blind listening tests have shown a consistently good correlation between perceived response and the room measurement.—Martin Colloms

Sidebar 2: Specifications

Description: Two-ribbon full-range transducer. Midrange and tweeter ribbon: 0.8" wide by 47" long, less than 0.001" thick. Woofer ribbon: trapezoidal, average width 12" by 47" long, average thickness less than 0.001". Frequency response: <30Hz-25kHz, -3dB. Crossover slope: 6dB/octave at crossover, increasing to 12dB/octave approx. two octaves away. Can be biamped with or without external active crossover. Maximum SPL: 106dB at 4 meters, C-weighted, using 100W solid-state amplifier. Nominal impedance: 4 ohms.
Dimensions: 58"H x 26"W x 3"D. Weight: 95 lbs each.
Finish: grey or taupe (beige).
Price: $2300/pair (1986); $2780/pair (1987); $2995/pair East Coast, $3100/pair West Coast (1988); no longer available (2003).
Manufacturer: Apogee Acoustics Inc., 35 York Ave., Randolph, MA 02368 (1990-1995). Apogee Technology Inc., 129 Morgan Drive, Norwood, MA 02062. Tel: (781) 551-9450. Fax: (781) 440-9528—no longer manufacturing loudspeakers (2003). Web: www.apogeeddx.com. Since Apogee no longer makes or services their speakers, readers can try www.apogeespeakers.totalserve.co.uk .