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Reviewer: David Kan
Source: Restek Radiant; Assemblage D2D-1/DAC-3 Signature; Pioneer DV-578A
Preamp: Symphonic Line RG3 Mk3; Restek Vector
Power amp: Symphonic Line RG4 Mk3; Sim Audio Celeste W-4070se
Speakers: Apogee Centaur Minor; JM-lab Micron; Dynaudio Facette
Cables: Symphonic Line Reference power/interconnect/speaker cables; OCOS speaker cables; Ensemble power cables; Orphee Audio Corda digital cable; Aural Symphonic Missing Link power cable; Clearaudio Silver Line interconnects; Artech Prisma speaker cables
Power conditioner: Tice Power Block IIIC; Deltec The Power
Stands: Custom; Stephen Desk Credenza
Accessories: Symphonic Line Audiobasis; JMlab Focal spikes
Room size: 12' x 24' x 9' opens to 12' x 17' x 9' L-shape, short wall setup; 15' x 15' x 8' for second room
Review component retail: Maximus $2,950/pr; Omni Harmonizer $900/pr
|To get deep, riveting bass out of a small bookshelf speaker is to get blood out of stone. Like it or not, it's one undeniable fact. Most of us have long since come to terms with it. Some -- myself included -- revert to subwoofers. Others learn to acquire the taste of musicality over dynamics and live happily ever after with legendary bookshelves from makers like Celestion and Rogers. But history is meant to be rewritten. Rules are meant to be broken. After all, in this wonderful world of HiFi, nothing is carved in stone or written in blood.
Mark & Daniel, founded in 2004, is a young company that set out to revisit the basic design of a 2-way bookshelf monitor. Cofounders Mark Wong and Daniel Lee first set up their drawing board in Tucson, Arizona. Later, they extended R&D operations and labor-intensive manufacturing to Shanghai, China. Mark, a retired American Chinese businessman, is a respectable Zen guru in the spiritual field. He believes that the pursuit of purity in music reproduction coincides with the goal of his soul life. Daniel, originally from Taiwan, was a long-haul telecommunication systems designer/project manager and serious audiophile for many years before becoming the second principal in Mark & Daniel.
Back to the drawing board. First, Mark and Daniel took one long hard look at driver FMD - frequency modulation distortion. FMD or Doppler Distortion is a transitional form of distortion that occurs when the driver diaphragm carries more than two frequencies at the same time whereby the frequency with the stronger sound pressure level causes the other frequency to fluctuate. You might say that a 3-way or 4-way speaker system would have less FMD distortion than a 2-way speaker system. Their drivers have a much easier job when each of them is covering a narrower bandwidth. Also, wider diaphragms in the woofers of large floorstanding speakers should handle dynamics with lower FMD interference. FMD affects tweeters as well. The traditional way to minimize it is to operate the tweeter over a narrower bandwidth. "Let's make sure the highs sound okay and don't worry too much about bass integration." Since most people are already habitually prepared to accept silkily smooth highs over not much low bass from small bookshelf monitors, such sacrifices make a lot of sense. But not to Mark & Daniel.
|How seriously has FMD been restricted in the design and ultimate performance of bookshelf speakers? Designers of traditional 2-way bookshelves have their hands tied in two ways (pun intended). First, the conventional 1" dome tweeter is restricted to a range of 2.5kHz (or 2kHz) to 20KHz. This translates into 3, hardly 4 octaves. The rest of the task, an unwieldy burden of 6 to 7 octaves, is dumped on the bass driver. Secondly and to keep FMD under control, the movement or displacement of the bass unit has to be optimized, which in the end limits useful bass output.
That explains why the crossover frequency of most 2-way speakers has been hovering around the 2.5kHz mark. To lower this transition point, Mark & Daniel redesigned their tweeter and turned it into DREAMS - Directly Responding Emitter by Air Motion Structure. To be honest, I find this nomenclature a bit of a contrived marketing gimmick. At the same time, I can't help but remember it. What's great about this unit is that it embraces a bandwidth of 5 octaves from 800Hz up to 22kHz. Modeled on German physicist Dr. Oskar Heil's AMT or Air Motion Transformer -- which found its way into the Electro Static Sound ESS hybrid speakers in the 70s and now the Aulos -- the M&D DREAMS is a new member of the AMT family. With a twist. As we know, a traditional cone driver has a coil of wire suspended inside the field of a permanent magnet. The coil is attached to a cone or dome-shaped diaphragm to produce sound. Hence the term voice coil. When a signal passes through the coil, the magnetic current moves the coil and diaphragm forward and backward, creating a sound pressure wave.
|While cone drivers work on the principle of pushing and pulling air, the air motion transformer creates sound waves by compressing/squeezing air. Instead of a cone or dome, the diaphragm of the AMT folds like the bellows of an accordion, forming a rectangular-sheet pleated diaphragm that's mounted vertically with coils and magnets on both ends. The electromagnetic fields cause the folds to squeeze and release, generating sound waves as a result. This scheme is said to result in a more efficient driver whose air mass/movement from the bellows action is 5 times larger and whose propagation velocity is 5 times higher than that produced by diaphragmatic push/pull action - 5.3 times higher to be exact. For this reason, the AMT is also known as the AVT, Air Velocity Transformer. Incidentally, Dr. Heil was the inventor of the Field Effect Transistor (FET) as well. It forever changed the concept and design in audio electronic technology as we know it today.
The AMT was another breakthrough. Not only did it yield much higher motor efficiency but it also provided a solution to the fundamental problems of diaphragm mass, inertia and self resonance. According to audiophiles of the time, music reproduction had never been so transparent. There was one problem, however. With then limited commercial availability of light-yet-rigid materials, certain Heil AMT units reportedly suffered "melted aluminium foil pleats". As the AMT patent expired and the usage of the design principle became public domain, many improved versions came to market.
The Mark & Daniel DREAMS tweeter installed on the Maximus Monitor (and other M&D models) is the DM-1 unit. One remarkable characteristic is its aforementioned bandwidth to 800Hz. Since the Maximus Monitor is bi-wired, one can compare its tweeter with a traditional bi-wired 2-way by merely connecting to their respective HF binding posts. I did just that with my JMlab Micron whose crossover point sits at 4kHz (one of the highest in this genre). Trust me, the difference is heaven and earth.
Sporting a unique curved pleated diaphragm of 3.5 inches wide and 3 inches high, the DM-1, itself measuring 6" wide x 5.25" high x 1.75" deep, is unusually large for a tweeter of its kind. According to system designer Daniel Lee, they experimented with diaphragms of different shapes -- flat, concave, convex -- and concluded that inwards curvature was ideal. Their driver has wide horizontal (+/- 30 degrees) but almost no vertical dispersion, thereby minimizing reflections from floor and ceiling. Technically, the DREAMS claims to surpass all mainstream 1" domes (and possibly Dr. Heil's original AMT) by achieving lower FMD distortion with higher output over its entire operating bandwidth.
How? Basically, by being lighter and bigger. The DM-1 utilizes a 10 micron (0.0004") ultra-thin aluminium ribbon which is symmetrically folded into 52 micro elements, constituting a diaphragm area more than 60 times that of a 1" dome while its attendant mass is less than 20%. The diaphragm is then submerged into a magnetic loop comprised of 21 Neodymium-Iron-Baron (NeFeB) magnets. The module is housed in a 5mm thick cast iron/stainless steel casing for rigidity. Average efficiency of the driver is as high as 91dB/2.83v/1m..
Now with 2 octaves off its back, the bass driver's mission seems lightened. But Mark & Daniel didn't take things easy there either. If there's any truth in the saying that a bass driver can be judged by its pistonic excursion, such believers have certainly been barking up today's tree. Mark & Daniel's secret weapon is the Super Xmax driver or SX for short. Far from a contrived pet name, Xmax (which stands for Maximum Linear Excursion) is the allowable linear excursion of a driver's cone before it gets into non-linear operation, i.e. bottoms out by hitting the magnets. Commonly expressed in distance (millimetres or inches), Xmax also reflects the maximum undistorted sound level pressure output.
As mentioned earlier, audiophiles have learned to accept the pathetic truth of close to non-existent bass from small speakers. Nobody wants to revisit the Xmax path again. Nobody cares to reinvent the wheel. But when I realized that what Mark & Daniel did was in fact so simple, I almost fell from the chair. Why didn't I think of it?
Let's examine the operation of a conventional bass driver in relation to Xmax. The pistonic movement of a voice coil is physically confined to the difference between the length of the voice coil and the height of the magnet - or more precisely, the magnetic gap in which the voice coil is suspended. The Xmax value is that difference divided by 2. Why 2? Xmax is a plus/minus value indicating the deviation from the stationary neutral position as the cone moves forward and backward. A conventional design always has the voice coil longer than the magnetic gap. A typical 6.5" driver has a voice coil length of 12.5mm and a magnetic gap height of 5mm. The Xmax therefore is: (12.5mm - 5mm)/2 = ±3.75mm
Can you obtain bigger bass output by increasing the Xmax value? Yes. By extending the voice coil and shortening the magnetic gap, you can get a longer throw. However, efficiency (in terms of dB) and internal damping (in terms of Qts) will suffer. Deterioration in efficiency is easy to understand. As pistonic movement increases in magnitude, it obviously requires more amplifier power to drive. Qts touches more aspects of speaker design and is a lot more complicated. In short, Qts is the Total Q (damping factor) of the driver, which is a combination of two opposing forces -- the Qms or mechanical suspension (the surround and spider) and the Qes or electrical suspension (the voice coil and magnet) -- which together act as shock absorbers and to prevent any lateral motion that might lead to a collision between the voice coil and magnetic poles. (To avoid degrading the Qts too much, an alternative would be to enlist more bass drivers in parallel but then you'd end up designing a floorstanding speaker.)
How did Mark & Daniel manage to change the law of physics? They of course didn't change any laws. They followed them but headed in the opposite direction. Remember how we said that pistonic movement had to work with a difference in measurement between voice coil length and magnet height? Instead of extending the voice coil and shortening the magnetic gap, they simply extended the magnetic gap to exceed the voice coil length. There are three M&D Super Xmax drivers. Their respective Xmax values are below:
As you can see, these Xmax values are subwoofer figures! M&D's patented SX technology also employs the expensive NdFeB magnet to ensure a very powerful and even magnetic field. A high-efficient ribbon copper voice coil is wound around a TIL fiberglass former that can withstand 250ºC. The ultra-large rubber surround is out of proportion for a driver of its size. The cone is tough compound paper and the frame is die-cast aluminium. As a final touch, the signal-carrying lead-out wires that run behind the cone are secured by being threading through rings of DuPont Matamax dampers, protecting them from vibration caused by the enormous firepower. What we have here is a super driver that delivers deeper undistorted bass at much higher levels with more than double the linear excursion and at least 7dB higher SLPs than conventional drivers of the same size.
In order to satisfy my own curiosity, I removed the woofers of my Dynaudio Facette [above] and Apogee Centaur Minor [below] from their cabinets to compare them with the SX bass driver. They are all 6.5" in diameter but the length of the magnet/iron core of the SX was more than double of the other two.