Diffraction is a re-radiation of sound when that sound encounters a discontinuity, such as from a cabinet edge (among other phenomena). Think of a soundwave emanating from a driver mounted in a baffle. Some of the sound travels along the baffle’s surface from the driver toward the baffle edge. When that portion of the soundwave encounters a sharp boundary, the sound doesn’t continue on its path but rather is re-radiated in all directions by the surface discontinuity. (The word “diffraction” comes from the Latin diffringere, “to break into pieces.”) This re-radiated sound is slightly delayed relative to the direct sound because it travels a longer path between the driver and your ears. When this delayed sound combines with the direct sound from the driver, the two waves interact constructively and destructively (reinforcement and cancellation), creating a series of very fine ripples in the frequency response at higher frequencies.
Cabinet-induced diffraction creates a mild form of comb filtering, a phenomenon in which the interaction of two identical signals of approximately equal amplitude, one of them delayed relative to the other, combine constructively and destructively to create a uniform pattern of very deep notches in the frequency response. These nulls are so deep, and so regularly spaced, that the frequency response looks like a comb. The frequency response peaks and dips caused by loudspeaker cabinet diffraction are much less severe than full comb filtering because the amplitude of the delayed energy is low relative to that of the direct sound.
I’ll give you a vivid example of what comb filtering sounds like. In the Doobie Brothers’ hit “Listen to the Music” there’s a break in the middle with just the vocal, guitar, and hi-hat. The famous “phasey” swirling effect on the vocal during this break is caused by comb filtering, but with the frequencies of the peaks and nulls sweeping up and down the audioband as the delay between the direct and delayed signals is purposely varied to create the swirling effect. Today such effects are created electronically, but back in the day the effect was called “flanging” because the engineer would vary the pressure of his hand on the flange of a tape reel to slow down the tape to create the continuously variable delay. Although such effects may be employed as artistic expression, we obviously don’t want our loudspeakers imposing such distortions on the music.
Every aspect of the M6’s enclosure is designed to minimize the deleterious effects that the box has on the drivers’ outputs. The mandate to eliminate flat surfaces or sharp transitions even extends to the contact point between the loudspeaker and the floor. Rather than rest on the floor on spikes, the M6 is suspended above the floor on a tripod arrangement terminated with Magico’s MPod feet. The bottom panel is rounded and curved just as the top panel is.
This enclosure design has other benefits. First, the inside of the enclosure is curved, reducing standing waves inside the cabinet. Standing waves are stationary areas of high and low pressure formed by sound waves reflecting from the cabinet interior surfaces and interacting with one another. Second, carbon fiber is extremely light and stiff, allowing thinner cabinet walls without sacrificing rigidity. The speaker’s internal volume can thus be substantially larger while keeping the speaker’s overall size manageable.
Looking next at the drivers, the three 10.5" woofers and single 6" midrange driver are updated versions of the graphene-infused Nano-Tech driver technology that debuted in the Q7. The motor is the same, but the cone benefits from a second-generation implementation of graphene, a wonder material that is extraordinarily strong but adds virtually no weight to the cone. According to Wikipedia, graphene is “a two-dimensional, atomic-scale hexagonal lattice in which one atom forms each vertex.” That is, this form of carbon isn’t a fiber or a nanotube, but a lattice structure just one atom thick. Graphene is 200 times stronger than steel by weight. To quote from my review of the Q7, which saw the debut of graphene in loudspeaker cones: “The combination of lightness and stiffness is the Holy Grail of driver design; the lightness allows the diaphragm to start and stop quickly by virtue of its low mass, and the stiffness prevents the diaphragm from flexing (and thus introducing distortion) under the stress of being driven by a voice coil attached near the diaphragm’s center. A light diaphragm can also provide superior low-level resolution; music’s very fine details are not obscured by the diaphragm’s inertia. Think about the very low-level components of an audio signal—the most delicate musical details of timbre, microdynamics, and ambience—applied to two drivers, one of them with a high-mass diaphragm and a stiff surround material, and the second with a featherweight cone and very compliant surround. It’s easy to visualize how, with the high-mass cone, music’s very fine structure would fall below the driver’s ability to move in response to the signal. The driver’s mechanical structures set a threshold below which no information can be resolved. But the lighter the diaphragm, the more powerful and sophisticated the motor structure, and the more carefully designed the surround material and shape, the lower that threshold becomes. The result is an increase in low-level detail. Moreover, lighter diaphragms more faithfully reproduce the leading-edge attack of transient signals, which translates to a greater sense of realism and better conveys microdynamic expression.”
The M6’s extremely light and stiff cones are driven by an immensely powerful motor made from neodymium magnets. In the midrange driver, the magnetic field strength in the gap where the voice coil sits is 1.7 Tesla, which is more than twice the field strength of conventional drivers. I had a demonstration of how powerful these magnets are while on a tour of the Magico factory. A 6" driver was placed on a metal table and I was invited to pick it up. The magnetic attraction was so strong that it felt as though the driver were bolted to the table. Driving very light cones with very powerful magnets is analogous to a sports car with a 700 horsepower engine in a small and light body. Incidentally, reducing weight in a car improves the three main performance goals—it accelerates faster, stops faster, and turns better (because there’s less mass that must change direction). A loudspeaker driver follows the same laws of physics; the lighter the cone and the more powerful the magnetic motor, the faster that cone can start, stop, and change direction, and thus more faithfully reproduce music’s dynamic nature.
The M6’s tweeter is a 1.1" beryllium dome coated by a very thin diamond layer applied to the dome through vapor deposition. The diamond further stiffens the already stiff beryllium dome to prevent any non-pistonic movement. This is the same tweeter in the Q7 Mk.II, replacing the original beryllium tweeter in the first generation of the Q7. Having heard the Q7 with the older and then this new tweeter, I can attest that the newer tweeter is significantly smoother than the one it replaced.