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Published July 15, 2001


Stax SRS-4040 Signature System II

Some audiophiles make a face when you mention headphones -- as though they smell something foul in the air. "Headphones?" they sniff. "I hate the way all the music comes from the center of your head."

Well, it can be disconcerting, but I kind of dig it -- signs of a misspent youth, I suppose. Plus, it can be ameliorated. With a HeadRoom processor, for instance -- or, in the case of the Stax SR-404 Earspeakers under review here, by having the diaphragm of the 'phone set away from your ear and angled, so the sound seems to come from in front of you.

Does it work? Kind of. You get less of the middle-of-your-head sensation than from most headphones, but the 404s are still headphones after all. But I'm getting ahead of myself -- I only brought it up because it's indicative of the level of detail Stax has gone into with the SR-404 Earspeakers and the SRS-4040 Signature System II of which they form a part. Stax has essentially examined everything about headphones and the SRS-4040 SSII's are their attempt to redefine the headphone experience. (Well, you could step up to their $6000 statement SR-007/Omega IIs, but you get the idea.)

The very pink of perfection . . .

The SRS-4040 SSII consists of a pair of Stax's SR-404 Signature Earspeakers and the Stax SRM-006t tube Driver Unit. The SR-404s are a refinement of Stax's Lambda Nova Earspeakers, which were the final iteration of Stax's Lambda series, a longtime staple of canny audiophile earphone users. The physical resemblance is complete -- like the Lambda Novas, the SRS-404s utilize large rectangular earpads which are affixed to the sides of your head with a complex adjustable spring/sling head rig that is relatively comfortable if somewhat blocky. My chief complaint with the apparatus is that the synthetic leather covering on the earpads gets sweaty and slick during long listening sessions -- and quick head movements can send the Earspeakers flying when the pad-to-skin adhesion ratio is thus undermined.

Stax, as the name might have clued you in, use electrostatic driver elements. These are quite different from typical headphone diaphragms and deserve an explanatory note. In an electrostatic speaker, a thin electrically-charged conductive membrane is suspended between two stators -- fixed electrodes whose value changes from positive to negative with variations in the musical signal. The membrane is alternately attracted to and repelled by the stators' changing charges. Since the membrane can be very thin, it is amazingly responsive -- and the thinner the membrane the more easily it is moved. The SRS-404 features Stax's thinnest membrane yet -- a scant 1.35, which is substantially lighter than the air it displaces.

Theoretically, several advantages accrue from electrostatic operation. For one thing, it's a push/pull system, so the driver stays under control throughout its range of motion. And, since an electrostatic system employs no magnets, there's no chance for hysteresis distortion -- which is the lagging behind of the magnetizing force as the magnetic condition of the voice coil changes with the musical signal.

Electrostatic headsets require specialized power amplifiers that can charge the stator and drive the "earspeakers"; the SRS-4040 SSII employs the SRM-006t, which uses FETs in the first stage and a pair of 6FQ7/5CG7 dual-triodes in the output stage. The SRM-006t accepts both balanced and single-end line-level inputs. It even obtains its balanced signal without employing transformers or inversion amplifiers in the signal path, thanks to the truly slick double-axis quad volume control Stax designed.

The SRM-006t is deep (16" from volume control to RCA input), but only 8" wide and 4" tall. Its top plate is perforated for ventilation and two daisy-like bulges in the center highlight the location of its 6FQ7/5CG7 dual-triode tubes. A large split volume control dominates the champagne-colored faceplate; its front half adjusts the left channel, while the rear adjusts the right. Beneath the volume pot, to its left, are three connections for Stax headphones (two for Stax's 5-pin "pro" connector; the other for Stax's older six-pin "normal" plug). The rear panel has connections for an IEC power cord, two pairs of RCA inputs, one pair of XLR inputs, an RCA output, a grounding post and a switch that allows you to use input 2 as either RCA or balanced XLR. The unit's output is not connected to the volume control -- it can be installed in a tape or effects loop.

It's a delightful thing to speak of perfection . . .

It might seem strange, but I'd say that it's almost as important that a headphone be comfortable than that it be accurate. If you just listen to headphones for pleasure, you might find this puzzling, but try recording for eight or ten hours in a row, monitoring through headphones, and the issue of comfort becomes over-riding. On the other hand, if the 'phones aren't comfortable, you might not listen to them as much as you otherwise might. The SR-404 is a bit of a mixed bag in this regard. It sits lightly enough on the head, but it isn't well-balanced -- it's sort of like having a pair of paperback books strapped to the sides of your head. You are forced to be graceful or the headset will go flying. And, as I said earlier, they make me sweat, YMMV. On the other hand, they were never uncomfortable or painful as the Grados can be after several hours of listening.

And they sound fantastic. You become a part of the soundfield, whether vast and borderless, as on the best techno, or intimate and personal, as on John Atkinson's recording of the Schulhoff violin sonata [Stereophile STPH 012-2].

From the start of my audition, I was suspended in the middle of the sound with the Stax. No detail seemed too small to escape the Stax's resolving power. Listening casually to Old Friends [Columbia 64780 3-CD box], the superb Simon & Garfunkel retrospective, one evening, I was jolted out of my reverie by a twenty-year-old prank. As Artie Garfunkel was crooning "So long . . . so long; so long . . . so long . . .," I was startled to hear Paul Simon shout "So long, already!" deep in the mix. Oh, I'd heard it a time or two before -- just never so clearly when I wasn't listening for it.

I also listened to tons of new recordings with the Stax combo -- and, if you want to hear what's going on in a mix, down to and including all edits, these guys will tell you. As an engineer's tool, they are almost in a league of their own.

That doesn't mean they aren't enjoyable to listen to. After watching The Two Jakes on AMC recently, I was still in a retrospective mood. Taking my cue from the recording of "Haunted Heart" that played under the end-credits, I cued up Charlie Haden and Quartet West's 1992 Haunted Heart [Verve 314 513]. I fell into the lush '40s' mood, buoyed along by Alan Broadbent's piano and Ernie Watts' astringent sax, following Haden's acoustic bass deep, deep into the past.

As in fiction, it's the little details that matter. Haden's bass sounded huge -- but not bigger than life. And Watts' sharp attack and brassy sound was informed by an early reflection off of some hard surface -- a wall, perhaps, or a plexiglass viewport in a studio gobo. Who knows?

But the details never obscured my musical satisfaction -- I wasn't more impressed by hearing that early reflection than I was by what Watts was playing. The Stax are eminently musically satisfying.

Not without flaw, however. Is anything?

But it’s vastly more amusing to talk of errors and absurdities. -- Fanny Burney

I found the Schulhoff incredibly revealing through the Stax. John Atkinson and I recorded it in Santa Fe's Loretto Chapel, a tiny jewel-box of a stone space with a springy wooden floor that actually amplified the room's sound through its tympanic action. It has an incredibly warm, almost living acoustic that belies the near-freezing conditions under which we made it. But what I love about John's recording is the way it captured the lovely sound of Ida Levin's violin in a remarkably reverberant room. The reverberations are pronounced, but in focus with Ms. Levin's attack -- they don't dominate the sound, simply reinforce it with a beautiful cushion of sound.

But while listening to Ms. Levin's vigorous performance, I heard a deep ripple in the soundstage -- it was almost like a special-effect in a movie, like the deep sub-bass synth tones that erupt during Clarice Starling's conversations with Hannibal Lechter in The Silence of the Lambs. Since I have listened to the Schulhoff recording literally thousands of times since we recorded it, I found this disconcerting.

Associated Equipment:

CD players: Musical Fidelity A3CD; Sony CDP-CX400; Slink-e

D/A converters: Bel Canto DAC1; Perpetual Technologies PA3

Preamplifiers: Ayre K1x; Conrad-Johnson Premier 17LS

Power amplifiers: Musical Fidelity Nu-Vista 300

Loudspeakers: Dynaudio Contour 1.3 Mk II, Thiel CS7.2

Cables: AudioTruth Midnight; DiMarzio M-Path interconnect; AudioQuest Dragon; DiMarzio M-Path; DiMarzio Super M-Path speaker cable; Illuminations Orchid digital cable

Accessories: Osar Selway Audio Racks, AudioQuest Big Feet and Little Feet, Vibrapods, Audio Power Industries Power Wedge Ultra 116

Room treatment: ASC Tube Traps, Slim Jims, Bass Traps

I listened to the Janacek and Enescu performances on the same recording -- both sonatas for violin and piano -- and couldn't hear anything resembling it. I checked the Schulhoff again -- sure enough, in passages where Ms. Levin vigorously attacked the strings, especially after silent passages, I could get varying occurrences of the ripple/bass distortion.

Speculating that the effect was either MIA or obscured in ensemble pieces, I turned to Beyond The Missouri Sky by Pat Metheny and Charlie Haden [Verve 537 130] and cued up "He's Gone Away," which is more a Metheny showpiece than a duet. Sure enough, on certain strongly plucked notes, the guitar sounded as though it was being processed through a reverb unit. What I think I was hearing was the electrostatic diaphragm vibrating sympathetically with the note -- or possibly being sent into oscillation. It doesn't last long, but it's inescapable once you've noticed it.

BTW when the stator was under control (reproducing a bass tone simultaneously, for instance), I couldn't get the Stax to reproduce the resonance ripple -- it only occurred with solo instruments at certain frequencies.

So how serious a problem is this? It's hard for me to say how much you'll object to it. I found it annoying, but relatively easy to ignore (and plan around). On the other hand, in a product that costs $2365, you expect that they'll have worked out these details -- especially when competing products costing one tenth its SRP are also pretty close to flawless. My reference headphone system of a HeadRoom Max and a pair of Sennheiser HD-600s doesn't have such an obvious coloration, nor did the older Stax Earspeakers with the thicker diaphragms -- at least not that I ever noticed.

It is through Art, and through Art only, that we can realize our perfection.-- Oscar Wilde

I can't deny that I spent hundreds of wonderful hours listening to the Stax SRS-4040 Signature System II. It seems petty to lose enthusiasm for them because of a few microseconds during one or two recordings -- but accuracy is like pregnancy: You either is or you ain't. Since I use headphones as a tool, as well as for entertainment, I have to trust what I hear. Unfortunately, good as they are, the Stax SRS-4040 don't quite rate that trust.

But maybe that level of accuracy doesn't mean as much to you as what the Stax gets right -- which is almost everything. In that case, you should hear these headsets. You may find them close enough to perfection to justify the price. If you do, I certainly wouldn't argue -- they come mighty close. And if all I did with headphones was listen for pleasure, I might even agree.

...Wes Phillips

Stax SRS-4040 Signature System II
List Price: $2365 USD
Warranty: Five years parts and labor

Stax Limited
293-1 Fujikubo, Miyoshi-Cho
Iruma-Gun, Saitama-Ken
Japan 354-0041
Phone: 81-492-58-3988
Fax: 81-492-58-2659


US Distributor:
Yama's Enterprises, Inc.,
206 E. Star of India Lane
Carson, CA 90746-1418.
Phone: (310) 327-3913
Fax: (310) 324-7422


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