Krell LAT-1 loudspeaker
Dan D'Agostino, the LAT-1's designer, arrived later and explained the phenomenon. The loudspeaker's name—the Lossless Acoustic Transducer, or LAT-1—refers to its all-aluminum enclosure, which is sonically inert to maintain pinpoint accuracy and resolution. Once the music began, the LAT-1 proved fast, highly detailed, ultradynamic, and rich in transient information. D'Agostino said that the LAT-1 would be priced at $37,500/pair.
Would the LAT-1's sonic performance match that of other high-priced flagship loudspeakers in sustained listening? Unfortunately, the answer was not to come that night. The power amplifiers shut down from low line voltage and refused to come out of standby. But I'd been bitten. I made arrangements to continue the audition in my own listening room.
A Bulletproof Design
The LAT-1 gets its solidity, density, and inertness from aluminum. Unlike the wooden body of a violin, which adds tonality that amplifies and sings along with the strings, a loudspeaker enclosure's storage and dispersion of such energy blurs the musical signal. No matter how well damped, wooden loudspeaker cabinets tend to store and then radiate acoustic energy, which colors the sound. Because aluminum does not store energy in the same manner as wood, Krell engineers predicted that little or no energy would be lost to the enclosure, enabling a nearly perfect "driver launch."
D'Agostino chose aluminum for other reasons as well. While concrete and lead are even more inert, cabinets made of such materials are prohibitively heavy, difficult to move around factory floors or load onto trucks, or to export or to install in homes. Aluminum is both inert and relatively light in weight. It combines structural rigidity, resonance damping, cost-effectiveness, and relative ease of manufacture. Krell engineers were already familiar with working aluminum, whether in a 200-lb Krell amplifier chassis or an airtight, immovable, 650-lb, all-aluminum Master Reference Subwoofer (MRS).
Aluminum enclosures are easier to store than wooden enclosures. Krell orders LAT-1 cabinet sections "just in time" from a machine shop in Colorado. This supplier cuts and shapes the raw aluminum sheets into precisely shaped enclosure sections. These can be stored like planks, not finished speaker enclosures, and thus take up much less room in the Krell factory. Furthermore, assembled wooden cabinets must be stored longer, because they require more time to finish, glue, varnish, and veneer before the drivers can be installed. A LAT-1 can be assembled and shipped in two days.
The LAT-1's aluminum walls vary in contour and in thickness. The cabinet top, bottom, back, and front baffle are cut to size from flat 6061-T6 aluminum stock. For the curved side walls, D'Agostino uses extruded 6063-T5 aluminum configured to vary from 1" to 1.5" in thickness, and with exterior ribs to eliminate the diffraction of high-frequency wavefronts. These curved surfaces and the speaker's inner baffles minimize internal acoustic standing waves while using a minimum of energy-robbing internal damping foam. Computer-optimized geometry for wall contours, internal port tubes, and internal baffles were also used to reduce standing-wave interference. A separate, computer-modeled subenclosure of ¼"-thick aluminum houses the midrange and tweeter drivers, and a foam surround isolates the subenclosure from the main enclosure. The LAT-1's base plate is a squared-off triangular plinth, wider than the speaker, that can be fitted with support spikes with adjusting knobs.
During assembly, each aluminum piece is rimmed with a rubber grommet that allows the panels to be screwed together to form airtight seams. Accelerometer data suggested that more damping was needed, so D'Agostino added three more internal cross-braces to further deaden the cabinet's structure. The finished LAT-1 enclosure is a dense, nonresonant shell that stores no acoustic energy.
Despite its weight, the LAT-1's narrow dimensions give it a small footprint and allow the speaker to be easily positioned in a multichannel setup—as I heard at the recent Home Entertainment 2001 show in New York, where Krell used four LAT-1s: right and left front, right and left surround. I found the LAT-1's sleek aluminum cabinets much less obtrusive and visually overwhelming than other high-end loudspeakers I've recently reviewed—and there were no "What's that?" comments from my wife.
The LAT-1's crossover is built on three circuit boards that extend the full internal height of the enclosure. The three-way crossover uses a third-order Butterworth design at 2.9kHz between tweeter and midrange, and a first-order network at 300Hz between midrange and woofers. The individual printed circuit boards are fashioned of 1/8" fiberglass with 4 oz copper traces. Large air-core inductors for the woofers are wound with oversize wire, while those for the midrange and tweeter use Litz wire, which is said to extend high-frequency linearity. D'Agostino explained that the high-current polypropylene film capacitors require potting in their own plastic cases to isolate them from pressure and vibration. Similarly, the high-power metal-oxide and wire-wound resistors are connected in parallel to minimize parasitic inductance and maximize power handling.
Each LAT-1 uses six ScanSpeak dynamic cone drivers, custom-made to handle high-powered Krell amplifiers. Set into a D'Appolito array at ear level, the 5.25" midrange units are positioned above and below a single 1" tweeter at the top of the LAT-1's front baffle. The manual states that the "midrange cones have five doped cuts, providing strength without the distortion that occurs when the entire cone is doped....The segmented cone of the midrange reduces self-induced resonance...while its asymmetrical spider lowers distortion. The dual concentric tweeter features a waveguide design that increases dispersion around its axis." This waveguide helps push the first resonance point above 44kHz, well above audibility.
Three custom-designed 8" drivers are used for the bass. Each employs a composite carbon-fiber cone and butyl surround, and a cast magnesium-aluminum frame optimized for use in a tuned reflex cabinet. The drivers have long excursions (1" peak-peak) for better power handling. The LAT-1 sports three computer-optimized reflex ports, each with an internal aluminum port tube.
The LAT-1's bar-and-rubber-cord grille was inspired by that of the Sonus Faber Amati Homage. D'Agostino admired the design so much that he wrote to Franco Serblin, president of Sonus Faber, for permission to use a similar approach in the LAT-1. The rubber strings decrease the reflective surface area while matching the ribbed configuration of the loudspeaker's enclosure. To attach the snap-on grille, you anchor the bottom bar, stretch the rubber cords until they're taut, and snap the top bar into place at the top of the front baffle.
The knurled binding-post lugs on the LAT-1's rear panel can be easily tightened without using pliers or wrenches. Only two posts are supplied; biamping is not possible.
The LAT-1's glossy, detailed, well-written owner's manual gives clear instructions for setting up the LAT-1's three spiked feet. These options are important for sound quality if the loudspeaker is to be placed on a carpeted floor. The steel spikes have rounded tips, so they're less likely to damage the floor. The two rear articulating spikes have a turning knob for precisely leveling the LAT-1 to optimize imaging and to reduce vibrations. While the two rear spikes can be installed by one person, two are needed to tilt the speaker back to install the single front spike. A bubble level is included to help in adjusting the rear knobs until the loudspeaker is level on the spikes.
The fit and finish of the all-aluminum cabinet are among the best I've encountered in any loudspeaker. The Krell LAT-1's rugged construction and robust crossover and drivers should keep it operating reliably for years. It seems truly to be a "bulletproof" design.