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April 2002
Enjoy the Music.com Review Magazine
Minimonitor Accuracy Earthworks Sigma 6.2

Review by Steven R. Rochlin
Click here to e-mail reviewer

Earthworks Sigma 6.2  Audiophiles seem to enjoy objects of art. Imagine the cost savings if an amplifier was made using a sensible cabinet versus 1/4" thick front panels that are etched with the company's name and model number, and then have it all gold plated. The same could be said for loudspeakers. Instead of using some over engineered extruded aluminum to make a Super Duper Designed Ultra-Lossless Enclosure as in a certain product namesake from a sci-fi movie and giving the product such a ego ridden and totally misleading name along the lines of Completely No Loss Acoustic Device (sic), you decide to build what may be a superior quality music reproduction product in a sensible cabinet. Better still, instead of farming out the acoustic design, you have the brainpower within your company.

The professional audio industry is not one easily ready to swallow some of the snake oil found within the high-end audio industry. While we may agree that everything about the human perception of hearing is not known, there are some things that simply make no sense... or "needlessly" add quite a bit to the retail cost of a product (as described above). Instead, the professional audio industry generally believes in results. While there are quite a few very high priced products in pro audio, there is usually a very justifiable reason that results in higher quality sound and flexibility. So forget the false claims and ego enhancing product names (and people), and instead insert hard working individuals hoping to bring products to market that allows one to produce better recorded music to the world.

This leads us to a company well known with many recording engineers all around the world. Earthworks Inc. has long been acknowledged to make recording studio quality and laboratory/measurement grade microphones. At the recent Audio Engineering Society (AES) convention in New York City (see our show report by clicking here) Earthworks received a very prestigious Technical and Creative Achievement (TEC) award in the Microphone Technology/Sound Reinforcement category for their SR69 cardioid microphone. Furthermore, the loudspeaker reviewed here won the 11th Annual EQ magazine Blue Ribbon Award for studio monitor in their March 2002 edition. After having a good dose of the Earthworks Sigma 6.2 loudspeaker while attending the AES 111th convention i requested a review sample.


Solid, Sane Engineering

The brain behind Earthworks is none other than audio inventor David Blackmer. David's claim to fame includes the dbx system with the Blackmer VCA and RMS detector. The dbx noise reduction system, dbx compressors (160 and 166), and dbx boom box subsonic synthesizer are his babies too. In fact if you have heard stereo television then you have listened to dbx processing! For many years Earthworks mainstay has been in the microphone industry. Not microphones that have their own beloved coloration (distortion) such as the tube amplification variety, but ultra-clean and precise measurement-grade microphones. Extreme accuracy has been key to many of their products and, in turn, given Earthworks Inc. critical acclaim worldwide. So why would such a successful microphone company decide to go into the loudspeaker business?

As with any audio product, there is a need to not just test it with measuring equipment, but also through critical listening. This lead Earthworks to the need of find a highly accurate monitor. After many different designs Earthworks finalized product was their Sigma 6.2 as reviewed here. 

After toying around with drivers from Manger and others in hopes of achieving ultra-wide bandwidth, the Vifa drivers received the nod for accuracy and the ability for extended frequency response to 40kHz. Each Vifa driver is carefully tested in Earthworks own extensive measurement facility and each set of loudspeakers uses carefully matched pairs. Speaking about their measuring techniques, to quote an e-mail i received from Earthworks "Our production measurements are done using MLSSA. We do use an impulse to show us where to position the tweeter in order to properly align it with the woofer in the time domain. There is much more which could be said about this but it is in the form a new model of human hearing... For microphones we use an electric spark as a near perfect impulse sound source. We analyze what we get back from the microphone."

Crossover components were also carefully chosen and consist of Solen air core inductors and Solen polypropylene capacitors. Loudspeaker binding posts are of the very durable gold plated WBT variety. While the impedance is rated at 8 ohms with a sensitivity of 87dB/W/m, the loudspeaker seemed easier to drive than i had expected. Looking at the impedance vs. frequency chart on their website shows the Sigma 6.2 to have a fairly stable impedance and always stays above 6 ohms. Sadly, it seems some audiophile loudspeaker manufactures still design products that go down to 4 ohms, or worse still, 2 ohms. The Sigma 6.2's sane impedance curve means it will be easier for amplifiers to drive.

Power handling is a healthy 150 watts continuous, with 400 watts peak for short periods. The main focus of the Earthworks Sigma 6.2 loudspeaker was to achieve as accurate a signal from the amplifier output to what the loudspeaker produces. David Blackmer feels that audio equipment with extended frequency response and faster, cleaner time domain performance will yield a more life-like result. 

"This is not just a loudspeaker," says David Blackmer, president of Earthworks. "We want our customers to be able to hear all of the detail and realism they are capturing with Earthwork microphones. We created the Sigma 6.2 with the wide range frequency response and excellent time response necessary to deliver that realism... They are great for playback of 96kHz recordings." Eric Blackmer, director of Sales and Marketing at Earthworks, said "We have applied the Sigma Six ideal to the playback transducer using the same principles which led to Earthworks microphones, those of time accuracy and fast, clean impulse response."

Yes, some mighty lofty claims indeed. Especially from a company that has never commercially produced loudspeakers. Of course if i had a dollar for all the hype read each month from manufactures i could have retired long ago in Italy driving a Ferrari F50 and visiting Germany's Nürburgring monthly for all out driving fun. Let us see if these claims are true, or more hype and hot air like the Completely No Loss Acoustic Device as one electronic manufacture (erroneously) claims with their new foray into the loudspeaker market.

And It Sounds Like...

As the Sigma 6.2 are for nearfield monitoring, i used them mainly in my own digital audio workstation (DAW) and also my main listening room. Nearfield monitoring tends to be less demanding on lower frequency response, as the loudspeakers are near you, hence the name nearfield. If you have ever visited a recording studio or seems photos of one, you have seen small loudspeakers on a shelf (or some such) on top of the rear section of the mixboard. Once you place loudspeakers further away from a listener such as most audiophile do within their listening room, bass support gets more dependant. Many factors come into play including loudspeaker positioning within the room, size of the room, and the acoustics of the room. While the above is not a completely thorough break down of the effects of loudspeaker placement and room concerns, they help to show how where you are within a room and loudspeaker placement can be a major factor to perceived music reproduction.

Within my DAW system the Sigma 6.2 were only about three feet from my ears and toes inward towards my chair. The music seemed to float well between and behind the loudspeakers. In fact the imagining was much tighter while the overall sound was cleaner than my current Reference 3A MM De Capo (see review by clicking here). The highs were also more extended and there was increased speed. The Reference 3A MM De Capo appeared were slightly smoother, richer in harmonics and has a touch more bass extension. For those looking for a microscope into the sound that includes ultimate clarity and precision, the Earthworks Sigma 6.2 may be the wisest choice. Considering the Sigma 6.2 is geared for recording studios, it would be a natural choice. Some audiophiles may prefer the smoothness of the Reference 3A MM De Capo. It is akin to the Sigma 6.2 being along the lines of the critically acclaimed Wilson Watt, yet more refined and not as brittle nor harsh as the early Wilson loudspeakers were. Since most people reading this article are audiophile and not recording studio types, it is time to move into my main listening room.

Placing the Sigma 6.2 on my sand-filled Sound Anchor stands that are 26" high, room positioning seemed best about four feet from the rear wall and about two feet from the sides. This made my favorite 60-degree angle from listening position to speakers (30 degree each from center line). Like all well-designed minimonitors with very closely matched drivers, the loudspeakers did an amazing disappearing act. Both front image width and depth were outstanding! The sheer precision and speed of reproducing the music signal was on par with the best my ears have heard in all these years. It always brings amazement to my friends when they sit in my listening chair and hear seamless music flowing within the room. This includes the audiophile "trick" of images also appearing outside the loudspeaker positioning (when in the recording).

Due to no boundary enforcement, the bass from about 100Hz on down was lacking. In fact from 50Hz on down there was virtually no apparent output at all. Of course a Rel or M+K subwoofer or, when the time is right, a matching Earthworks subwoofer would be the order of the day. As i said earlier, think of them being like the early Wilson Watt, yet further sorted out. The pristine clarity was on par with my reference Avantgarde Acoustic hornspeakers, though there was hint of midrange boost. This type of boost seems to be great for enhancing the effect of more precision in imaging. The Sigma 6.2 was not fatiguing as the early Wilson Watts could be. This may also be due to the fact of more refined electronics and better cabling since hearing the original Wilson Watts with Goldmund gear and MIT cable many years ago.

Harmonically, these speakers are not "warm" nor "lush", what is heard in my listening room is very fast, precise sound. During the usual multi-channel, multi-mic'ed commercial pop recording i can easily hear when effects are inserted (punched in) and faded out. Same goes for the usual volume adjustments of various channels in those 32+ channel mix board/channel recordings. Think of the Sigma 6.2 as a microscope into the sound. In fact changes to cables, amplification and other upstream gear is more apparent. This is also one of the great things about the Avantgarde Acoustic Duo 2.0 hornspeakers, but to a slightly lesser extent.

The real question may be do you, as an audiophile, want to hear all this detail? You may find that many recordings you felt you knew intimately have more information than you realized. Of course all this accuracy is a double-edged sword. The good, the bad, and the ugly will be there is startling realism for you to hear. The Linn Sizmik 10.25 self-powered subwoofer (as reviewed here) was a very good match for adding the lower frequency support i felt was needed. My fave and long out of production dual 12" M+K MX2000 self-powered subwoofer simply did not go high enough into the midbass region to form a seamless mate to the Sigma 6.2 minimonitors. Therefore if you are looking for full-range music reproduction you may want to investigate getting a pair of subwoofers such as the Linns.


Accuracy, Pure And Simple

While it may be hand for some to understand the Earthworks Sigma 6.2 being a bargain at $3,000 per pair, imagine a speaker withy the same tweeter as the Krell LAT-2 that retails at $9,500 per pair yet is designed for ultimate precision. Of course the Wilson Audio Watt 6 (sans Puppy) at $9,300 per pair is another alternative in this category. Keeping all this is perspective, the Earthworks Sigma 6.2 seems to be an all out bargain. While it lacks the aluminum esthetics of the Krell or the virtually bombproof piano black cabinet of the Wilson, Earthworks appears to have instead opted for solid, well-designed cabinetry and the best parts they could find. Then take these parts and use a combination of critical listening with laboratory measurements to achieve a very high-resolution minimonitor loudspeaker design. Carefully match all drivers, time align it all, and there you have it. This design is not "pleasant sounding" with rolled-off highs, slight dip in the upper midrange, and/or a boost in the midbass region like some fave audiophile objects of art. If you desire a highly accurate loudspeaker for ultra-critical listening (as needed in the recording studio environment), then the Earthworks Sigma 6.2 is a must audition. Of course in the end what really matters is that you...

Enjoy the Music,

Steven R. Rochlin


PS: It saddens me to report that David Blackmer of Earthworks passed away on March 21st 2002 at the age of 75. This happened only days after this review was written. Earthworks will continue manufacturing their products with David's son Eric assisting on the company's operation. David will be missed by his family and many music lovers worldwide.




Sub-bass (10 Hz - 60 Hz)


Mid-bass (80 Hz - 200 Hz)


Midrange (200 Hz - 3,000 Hz)


High-frequencies (3,000 Hz on up)






Inner Resolution


Soundscape width front


Soundscape width rear


Soundscape depth behind speakers


Soundscape extension into the room




Fit and Finish


Self Noise


Value for the Money




Frequency Response: 40Hz to beyond 40kHz (±2dB)

Drivers: Tweeter: Vifa XT25
            Midrange/Woofer: Vifa 6.5" with die-cast
            aluminum frame
            Note: All drivers are carefully
            matched in each pair

Binding Posts: Gold plated WBT

Inductors: Solen heavy gauge air core

Capacitors: Solen polypropylene

Other Details: High quality silver solder, OFC copper wire, all components custom selected and integrated, creating matched pairs, point-to-point crossover construction, high-efficiency internal absorber

Impedance: 8 Ohm

Sensitivity: 87dB/W/m

Power Handling: 150 watts continuous
                       400 watts peak

Weight: 32 pounds

Shielding: Fully Magnetically Shielded

Price: $3,000


Company Information

Earthworks, Inc.
P.O. Box 517
Wilton, NH 03086

Voice: (603) 654-6427 
Fax: (603) 654-6107
Website: www.earthworksaudio.com













































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