Genesis II.5 loudspeaker system Page 2
Three tweeters are used in a vertical array to approximate the midrange ribbon's line-source radiation pattern. The top two tweeters roll off at 8kHz, with the bottom tweeter run out past 20kHz. The rear tweeter is wired out of phase (as you'd expect in a dipole), and thus helps propel more high-frequency energy into the room. The rear-firing tweeter has an acoustical output equal to that of the three front-firing tweeters combined. The bigger Genesis II uses 12 tweeters on the front, the Genesis I uses 20. In addition to approximating the ribbon's line-source radiation pattern, using multiple tweeters increases the system's dynamic range, clarity during loud passages, and sense of ease on musical climaxes. With the treble energy distributed over so many tweeters, the excursion of each of them is minusculethey simply don't have to work as hard. Using more than one but less than many tweeters will, however, produce a strong lobing effect which will radically change the tonal balance at different listening heights.
The crossover frequency between the woofers and ribbon midrange is user-selectable from 70Hz to 125Hz via the remote control (the nominal setting is 85Hz). Note that this adjustment doesn't change the ribbon's low-frequency point, but only how far up the woofer goes. No matter what the crossover frequency, the woofers roll off at 12dB/octave to the midrange. The midrange cuts off at 4.2kHz with a second-order slope.
As you'd expect from a loudspeaker with this sophisticated a driver complement, the II.5's crossover is first-rate. The capacitors are custom-made foil-on-plastic film types (they weigh about ten times what a similarly sized conventional metallized film-type cap weighs), and use copper leads. The inductors are a unique copper foil type with multiple taps. These multiple taps provide a means of contouring the midrange's high-frequency rolloff to match the listening room's acoustic character. The II.5's rear-panel switch simply selects a different tap off the inductorno additional components in the signal path.
The wings of the enclosure, which are made of 1.5" MDF and laminated with plantation-grown Brazilian rosewood, reinforce the midrange driver's acoustic output between 100Hz and 500Hz. The baffle on which the drivers are mounted is also 1.5" MDF, and the woofer enclosure is braced 1" MDF. Although you may be tempted to move the II.5s by grabbing their wings, you should push instead on the woofer enclosure.
The II.5's finish quality is absolutely gorgeous. The rosewood wings are beautifully made, and put the II.5 among the best-finished loudspeakers I've seen. In addition, the veneers on the four rosewood panels are cut from the same piece of wood to ensure that the grain matchesan expensive touch. However, the II.5 looks better from the front than the rear, which holds the black-painted MDF woofer enclosure.
Paul McGowan designed the servo amplifier. It has balanced and single-ended inputs, and a pair of custom jacks for connecting the 30' woofer cable to the II.5s. This cable, made by AudioQuest and terminated with Swiss-made Neutrik connectors, delivers power to the woofers and returns the accelerometer output to the amplifier. The servo system was designed around this cable, which is essentially removed from the equation by the servo action.
A front-panel LED display shows the amplifier's operating conditions. You can change the woofer drive level, system low-frequency extension, woofer high-pass frequency, and woofer phase (in 5° increments)all from the remoteand receive visual feedback from the amplifier's front-panel display. The woofer high-pass control adjusts the system for the room, taste, and associated electronics. For example, raising the woofers' cutoff frequency increases the amount of midbass. Between the rear-panel midrange contour, rear-tweeter level control (2.5dB adjustment), and the servo amplifier's many adjustments, the II.5 system has sufficient variability that it will match most roomsor drive the owner crazy trying to figure out which settings sound best.
The all-discrete amplifier uses a total of six pairs of 30A bipolar transistors to achieve a power output of 400W RMS/channel. The power transformer is a large, 1.2kVA toroidal type. A unique limiter circuit senses when the power-supply rails begin to droop, then begins limiting the signal so the amplifier isn't overdriven. This is an innovative alternative to protection circuits in series with the audio signal.
Overall, the Genesis II.5 is a serious engineering effort. The custom ribbon drive-units, servo-driven woofers, powerful servo amplifier, and gorgeous woodwork all reflect a commitment to making a world-class loudspeaker. The Genesis II.5 is the antithesis of crank-'em-out cones in boxes.
Despite this impressive build quality, I experienced several problems with the review samples. First, an output transistor in the servo amplifier wasn't bolted to the heatsink, causing the amplifier to shut down after the first hour of use. When the transistor burned, it took out the rest of the output transistors for that channel. The second servo amplifier ran very hot, and shut down after playing for long periods at high playback levels. However, this happened only on hot days; I kept a fan handy for cooling down the amplifier during breaks in the listening (footnote 4).
Next, the left loudspeaker suddenly developed less treble energy than that of the right loudspeaker. The problem was a bad solder joint on a capacitor, which I fixed. Finally, about two months into the auditioning, an intermittent oscillation developed in the woofer's servo circuitry, making the woofers go crazy. Under Paul McGowan's instructions, I changed a resistor in the servo circuit (from 68k ohms to 75k ohms), which fixed the problem. This was apparently a delicate aspect of the design, because the resistor was socketed for easy replacement. This woofer servo instability and the amplifier's tendency to shut down were particularly annoying, occasioning Musicus interruptus at the most inopportune moments.
These bugs have reportedly been corrected in later production (I got one of the first pairs made)the servo amplifier now has larger heatsinks located outside the chassis, and the servo loop has been stabilized. Nonetheless, I would not have been happy had I spent $22,000 and experienced these problems.
With the II.5s properly tweaked in, their sound was absolutely stunning. This loudspeaker does things only hinted at by conventional designseven those costing several tens of thousands of dollars. In every listening session, I heard things in my favorite music that went unresolved by lesser loudspeakers.
The dynamics of the II.5s are unlike any I've heard from other loudspeakers. The II.5s were able to handle huge dynamic contrasts, with a sense of effortlessness on musical peaks. It's not just that the II.5s played loudly, but they were able to resolve the smallest of musical details and present the crescendos of a symphony orchestra at full tilt with lifelike levels. Moreover, the II.5s presented a sense of immediacy, slam, and sheer physical force that made listening to music a visceral experiencejust like you get from the live event.
Footnote 4: The problem of the servo amplifier shutting down disappeared when the ambient temperature was lower than 70°F, and should be solved altogether by the revised amplifier's external heatsinks.