Oct 27, 2004 7:01 PM, By Arthur Bloom

PRO SELF-POWERED NEAR-FIELD MONITORS

ATC designs and builds its pro audio and high-fidelity loudspeakers in the idyllic countryside of Gloucestershire, one of England’s more pastoral regions. But ATC’s new self-powered SCM20A near-field monitors would not be out of place in Star Wars—the aluminum, sloped, two-way, SCM20As in Darth Vader-black and Death Star-gray are ruthless and indestructible little tanks that incorporate some of the most sophisticated driver technology on this planet.

As soon as I received the SCM20As, I connected them to my Alesis X2 console’s studio outs and cranked up a DAT. Frankly, at $4,595 a pair, I expected the 20As to sound better. However, when I switched to the X2’s control room output connections, the sound improved dramatically. In other words, the speakers revealed a problem with my console that I had not noticed on lesser speakers. Indeed, in the weeks that followed, I learned that while they do not always tell you what you want to hear, the SCM20As tell it like it is.

To purify the sound chain and hear just how good the speakers really were, I connected them directly to a Meridian 508.20 CD player and 566 DAC, with a 518 digital processor for volume control in the digital domain at 72 bits. Reproducing pristine audio, the ATC20As were among the best-sounding speakers I have ever heard. It was as if someone had wiped away the scrim of distortion I have become accustomed to hearing from other speakers. Orchestral instruments retained their character rather than melding together. Hip hop samples were as sharp as daggers; rock was pure beef; featured vocalists were clarified from their surrounding backups; subtleties and flaws were laid bare.

The 20As are heavy for their size and have an attractive, if unusual, shape. Edges are rounded to minimize diffraction with the sides sloping in toward a gill-like heat sink in the back. The 66-pound speakers measure just under a foot-and-a-half tall, so finding a place for them requires care. My console perches provided only precarious support, and I found that Sound Anchors’ rock-solid adjustable stands provided a better solution (Mana Acoustics, which has built stands for ATC’s larger speakers, may build one for the 20As). Omnimount fittings built into the cabinets allow them to be attached to a wall or ceiling for fixed installations. The cabinets also feature built-in handles on top.

At the heart of the 20As are the soft-dome drivers that ATC meticulously manufactures. Unusually short voice coils are hand-wound from a specially milled flat copper wire and remain immersed in the magnetic flux at all times. Maximum excursion is 40 mm—almost an inch-and-a-half. The magnets themselves, at 20 pounds each, are massive. On the outside, the domes and cones are doped with a dampening compound ATC has developed to help dissipate extraneous radiation. Inside, active fourth-order crossovers at 2.8 kHz are individually aligned and phase-corrected. ATC has also developed an insulating sleeve (now included on all its drivers) to eliminate distortion caused by magnetic eddies. The eddies flow in minute areas of the front plate and pole piece adjacent to the voice coil, turning the soft iron into mini-transformers. Because the area is small, the concentrated current becomes strong enough to introduce distortion (at the third harmonic) into the signal flowing through the voice coil.

Since the 1930s, scientists have sought an electric insulator that features favorable magnetic properties and is not prohibitively expensive. ATC has developed a material from sintered (individually oxidized particles of) soft iron dust. Pressing the dust under pressure makes it stick together and act almost like a ceramic. Although not cheap, the material functions as an electric insulator while retaining the requisite magnetic properties. By adding sleeves made from this material to the pole tip and front plate, ATC says that it has reduced third-harmonic distortion by 15 dB. Although all dynamic drivers are subject to the distortion caused by these eddies, in most speakers it is eclipsed by the greater degree of mechanical distortion. For all but the best drivers, this incremental improvement would be imperceptible.

Another feature of the 20As that distinguishes them from most other active near-fields is the sealed-enclosure design. With no port or passive radiator, the 20As have a linear frequency of 80 to 12k Hz (±2 dB) and a 6dB drop at 60 Hz and 20 kHz. While a bass reflex would lower the cut-off, it would also incur a radical drop below that frequency. The 20As’ air-suspension design offers a more gradual roll-off and, with a Q of 0.5, practical bass response extends below 60 Hz. An EQ control knob on the back of the cabinet provides up to 6 dB of boost at 40 Hz. While low bass is not prominent, the sealed enclosure helps the speaker sound tight and well defined.

Because the sealed enclosure also limits sensitivity, ATC has provided each driver with ample amplification. Each 8-ohm, 150mm mid/bass driver is driven by a conservatively rated 250W Class-A/B amplifier; each 6-ohm, 25mm tweeter is driven by a 50W Class-A amplifier. Together, the 20As can deliver continuous SPLs of 108 dB at 1 m without a hint of distortion. Another 10 dB of headroom are available for transients. Numbers aside, these things can move some serious air. I had to consciously resist their seductive muscle for the sake of my hearing; my eardrums do not feature the bullet-proof protection circuitry that safeguards the drivers in the 20As.

Alan Ainslee from ATC agrees that the 20As could be used as midfields. “While conventional near-fields tend to be more directional, the 20As’ midband dispersion is broad and even, with the reverberant and direct sound fields closely matching,” he says. In other words, one need not stand directly in front of the 20As to enjoy their flat frequency response.

Presence Studios owner Jon Russell, who recently installed a pair of ATC’s flagship SCM300A main monitors, was kind enough to allow me to compare them with the 20As. The 300As reproduce music with such phenomenal vitality, detail and depth that they share more in common with live music than with typical loudspeakers. Next to the superlative 300As, with their enormous reservoir of power and headroom, the merely outstanding 20As were less transparent.

Nonetheless, for one-fifth the price of the $22,000 SCM300As, the 20As deliver a reality sandwich I have yet to taste from another near-field. As ATC’s Ainslee points out, their exceptional accuracy, linearity and low distortion are more characteristic of an amplifier than a speaker. Thus, while $4,595 is not exactly chump change, for monitors of this caliber, it represents a very good value. And ATC includes two black flight cases that could easily pass as Darth Vader’s carry-on luggage.

ATC, www.transaudiogroup.com.