Earthworks Sigma 6.2 loudspeaker
By John Atkinson   •   June, 2003 When I unpacked the review samples of Earthworks' Sigma 6.2 loudspeaker, I was reminded of a Pop Art exhibition I'd visited 30 years before, in London. Along with a stuffed drum kit and other of Claes Oldenburg's exaggerated-scale floppy sculptures, hanging from the Tate Gallery's ceiling was an enormous three-pronged, US-style AC plug made entirely of hardwood (footnote 1). Although the Sigma 6.2 is available in plain-Jane black MDF for $3500/pair, the optional solid-cherry cabinet, with its polished grain-streaked panels, has the same carved-from-solid, feel of the Oldenburg plug. I found myself wanting to stroke the speaker.

Earthworks...
...is a pro-audio manufacturer best known for its superb microphones (footnote 2). Founded by the pioneering engineer David Blackmer, the "db" of dbx fame, who sadly passed away in April 2002 at the age of 75, the company is now run by David's widow, Heidi Heller-Blackmer, and his son Eric, who is director of sales. The Sigma 6.2 is Earthworks' first loudspeaker, and is a fairly small two-way design intended to deliver "precision, time-accurate soundfield reproduction."

The Sigma 6.2's striking-looking cabinet features a triple-stepped front baffle. The bottom frontmost section carries the woofer; the center section has mounted in front of it a flat plate that carries the tweeter; and the top section has a rectangular slot, 6" wide by 1.3" high, that reflex-loads the woofer and makes a convenient handle. Both drive-units are made by Vifa in Denmark. The tweeter is the well-regarded dual-concentric, 1" dome unit, the woofer a 6.5" polypropylene cone built on a cast aluminum chassis. The crossover is a first-order type using Solen polypropylene capacitors and air-cored inductors; together with the stepped-back tweeter baffle, it is claimed to give a time-coherent presentation.

The tweeter is mounted slightly off-center on its sub-baffle. Both a Speak-on connector and a pair of WBT binding posts are provided in a recess on the rear panel of the Sigma 6.2's surprisingly deep enclosure. The speaker's fit'n'finish is to a gratifyingly high standard, though my erstwhile woodworking neighbor, Wes Phillips, was bothered that the grains on adjacent panels intersected at right angles rather than continuing across the joints. Me, I liked the effect. Claes Oldenburg would, too.

Sound
Earthworks recommends listening to the Sigma 6.2 rather closer than is normal for a domestic high-end speaker: from 3' to 9' away. After some experimentation, I ended up with the speakers a little farther out into the room than usual, which placed them 9' from my ears. If I sat closer, or moved the speakers farther out into the room, the bass was too shelved-down for my taste. At the position I ended up with, the low frequencies were still a little lightweight but extremely articulate. Though Earthworks claims the speakers are delivered already broken-in, I found that the lows loosened up slightly over the first couple of weeks.

The Sigma 6.2 was not your typically boomy reflex speaker. Stewart Copeland's kick drum on the second half of The Police Live SACD (A&M Chronicles 069 493 608-2) sounded superbly defined, and remained acoustically separate from Sting's bass. Using the 1/3-octave warble tones on Stereophile's Test CD 3, I judged the Earthworks' in-room extension to reach 50Hz, with some useful output still apparent at 40Hz and (undoubtedly helped by the room) 32Hz.

Pink noise sounded even and well-balanced as long as my ears were level with or below the tweeter, which was 35" from the floor on the tallest stands I had available, the 24" Celestion Si's. The Sigma developed a hollow-sounding coloration if I rose even slightly above the tweeter axis, suggesting that 30" stands would be optimal. In a recording studio, of course, the speakers would be placed above the console, which is, I assume, why Earthworks has arranged for the optimal balance to be heard on or below the tweeter axis.

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Footnote 1: The memory is vivid—I even took a photo—yet peculiarly, I can find no references to this work. Web links about Oldenburg typically mention just the floppy version, or the giant steel version half-buried in the ground at Oberlin College.

Footnote 2: I own a pair of Earthworks QTC-1 wide-bandwidth omni recording mikes, and use an Earthworks microphone preamp for Stereophile's loudspeaker measurements.