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Reviewer: John Potis
Analog Source: Rega P9 turntable, RB1000 & Hadcock GH Export arms, Benz Micro MC Silver, Rega Super Elys & Garrott Bros Optim FGS Cartridge
Digital Source: Accustic Arts Drive 1/Audio Aero Prima SE DAC
Preamp: Bel Canto Pre2P
Power Amp: Art Audio Carissa, Bel Canto e.One REF1000 and Canary CA 160s, Musical Fidelity A5 Integrated; Melody M880s [on review]; SilverTone Audio Model 3.2 [on review]
Speakers: Hørning Perikles, Anthony Gallo Acoustics Reference 3.1, Ohm Acoustics Walsh 4 with 4.5 mk.2 upgrade, Tidal Audio Piano
Cables: JPS Labs Superconductor and Superconductor FX interconnects and speaker wire, Furutech Digi Reference digital
Power Cords: ZCable Heavys, Red & Black Lightnings, JPS Power AC, Analog AC, Digital AC and Kaptovator power cords
Powerline conditioning: Balanced Power Technology 3.5 Signature Plus with ZCable Cyclone Power Cord
Sundry accessories: Sound Mechanics Performance Platform, 2-inch Butcher Block platforms with Quest for Sound Isol-pads, Vibrapod Isolators and Cones, Ultra & Heavy Zsleeves, Viablue QTC spikes under speakers, Auric Illuminator
Room size: 12' by 16' with 9' ceiling
Review component retail: $1,650

Some time around 1985, I made what to others around me looked like one of the most unbelievable of purchases. I bought the Stax Lambda Pro earspeaker system. $800 as I recall was the price of that system at the time. It seemed like an extravagant acquisition even by my standards. As it turned out, it was one of the best purchases ever. I was single and an apartment dweller. Being a good neighbor but late-nighter, I used the crap out of that system. I adored it. So detailed, so airy. So real sounding. In those days, the magazines made it out to be perhaps the best sound attainable by the average Joe. Better than any affordable speaker. I'll never forget the night I was sitting on my sofa positioned in front of a big sliding glass door. It was opened to the outside at the time. I was listening to Pink Floyd's The Wall. I don't remember the exact cut but I heard a sinister voice come from behind me outside the sliding door. It sounded incredibly real. It was very late. And it startled the beejeezus out of me. My heart still begins to race when I think about it. As I said, those cans could sound incredibly real. Also notice that I didn't say how the voice came from within my head. It was clearly outside my room. Cool trick from headphones - er, earspeakers as Stax insists on calling them.


I used that Stax system for years until around 1994 when I gave a listen to the Sennheiser HD580, a set of cans that was getting a ton of positive press. Well, that was it for my Stax Lambda Pros. There was no going back to them. Sure, they were still the most fatigue-free system I'd never heard - and the most comfortable too. Smooth and uncolored? Still the king. But the Sennheisers were exciting to listen to. They had bass power the Lambda Pros only hinted at. They also had a more forward sound that suited most of my music in a way that the Stax system didn't. In short order, I sold the Stax system to my brother-in-law who still owns and uses it. At something around 20 years old, it works perfectly and is in great shape. This testifies to how well built and designed Stax products are. So it was with a deep sense of both curiosity and nostalgia that I set out to obtain the SRS 4040II Signature system for review. In most respects, it looks very much like my old Lambda Pros. But that's where any resemblance ends completely.

The SRS-4040II Signature system is comprised of the SR-404 Earspeakers and the new SRM-006t II valve amplifier/energizer ($530 and $1190 respectively when purchased separately). Energizer? Yes, these are electrostatic earspeakers and like all such beasts, they require that the stators sandwiching the vibrating diaphragm be charged. Of course this is in addition to the usual musical signal, which is why electrostatics cannot be plugged into conventional headphone outputs.


As a system, the SRS-4040II Signature system resides mid pack in the Stax line. The SRS-007II (valve) and SRS-717 (solid-state) systems are the co-flagship efforts and retail for $3,895 and $3,600 respectively. On the other end of the spectrum are the $325 portable SR 001 MK2 system and the $575 SRS-005II in-the-ear system and the $700 SRS-2050II 'Basic' systems, the first in the line featuring full-sized electrostatic elements. At $910 and $1,000 respectively, the SRS-3010 and SRS-3030 systems round out the line though all Stax headsets and driver amplifiers are available separately.
Accompanying pictures will go a long way toward describing the SR-404 headset. What you should know is that the unit, sans cables, weighs only 10.6 ounces. The extremely pliable 8-foot cable brings the total to only 1.05 pounds. The SR-404 earspeakers are indeed large and they fit the head in a way that they never touch the ears. This spreads their featherweight mass over a great amount of surface area against the head. A minor amount of ear sweat is still a minor issue but the SR-404s can be worn for hours on end in complete comfort. The easily annoyed may resent the fact that pressure against the head is so low in fact that leaning forward to pick up the remote may cause the headset to shift or slip off. Me? I appreciated the comfort. The SR-404s pads are covered in very soft synthetic leather and -- based on my experience with the Lambda Pros -- will stay that way indefinitely.


Also of interest is that the padding is thicker at the rear than front in an effort to maintain perpendicularity with the ear, the ramifications of which I'll get to. The SR-404 is rated for a frequency response of 7Hz - 41kHz, no tolerance given. The new SR-404 Signature utilizes a new diaphragm only 1.35 microns thick as compared to the 2 microns of my former Lambda Pros and the 1.5 microns of the Lambda Nova Signature. A thinner diaphragm means less mass which is said to improve overall sound quality and the retrieval of inner detail.


The SRM-006tII is a vacuum tube amplifier described as operating in Class A. It utilizes two Electro Harmonix 6FQ7/ 6CG7 tubes. The SRM-006tII claims a frequency response from DC to 80kHz and provides the previously mentioned energizing voltage of 580 volts into two outputs. The SRM-006tII measures 7.7 inches wide x 4.1 inches high x 14.8 inches deep and weighs 7.5 pounds. The SRM-006tII's front panel features a large dual-concentric volume/balance control, two sets of earspeaker outputs, a power switch and push-button input selectors for up to three sources. Around back are those three inputs, one of them XLR. Additionally, there's a chassis grounding post and a set of RCA through-puts that send the input 1 signal to an optional amplifier should you wish to use the Stax as preamp in a speaker system. An IEC power inlet rounds out the ins and outs. The SRM-006tII has a handsome aesthetic about it and build quality was pretty good but not quite up to the standards of top-shelf components. The stamped cover was noticeably thinner than most and thinner than that of my previous Stax amp. That said, there was nothing flimsy about the rest of the construction. The base was solid and all connections, switches and buttons have a quality feel


In terms of break-in, I was warned that the 4040II Signature system would require about 200 hours of playtime before both amp and earspeakers were optimized - though more subtle changes continue for up to a year. I was told that the sound elements are hand-manufactured using thin film membranes stretched between the perforated metal sheets - the stators that carry the aforementioned charge. Though evenly stretched during manufacture, there will be microscopic irregularities. Playing music causes the thin film to stretch out evenly throughout the vibrating surface.
Out of the box, the 4040II Signature sounded heavy and thick - the antithesis of what I had expected. So much so in fact that at first, I feared something was wrong with the system. As I'd been warned, things improved considerably with 200 hours of play. However, in some ways they never did meet my expectations.
As compared to my old Lambda Pros (I borrowed them back for comparison), the 4040II Signature system never achieved the same level of transparency. Neither was it quite as open and airy. So strong is my memory of the Lambda Pros that upon commencement of each
listening session, I was reminded of this discrepancy. But that wasn't really a bad thing. The new 4040II Signature is vastly improved in those areas where the Lambda Pros had eventually failed me.


Where the Lambda Pros were light and airy, the 4040II Signature is dense and meaty, with much greater harmonic embellishment - relatively speaking. While remaining quite linear, the bass was hugely improved over the Lambdas. Much more solid, the 4040II Signature has the kind of bass foundation its predecessors never did. And it's married to a much more robust upper bass. When all is right, this is one area where headphones are a trade-off against really good speakers. The Stax system is incredibly flat and natural here in a way that real speakers in a room usually aren't. That's the good news. The trade-off is the same as with all headphones. The palpable bass energy both in the gut and floor is missing. You will, however, sense a good amount of energy through your head itself. Which you will prefer is a matter of taste. There's no doubt that the bass is now more natural and linear through the 4040II Signature system than either with my Grado SR80s and Sennheiser HD 580s, both of which sound slightly exaggerated and contoured by comparison. The big bass drums on Peter Gabriel's Security [Geffen 2011-2] for example have excellent weight and detail, with no undue bloom or boom but with excellent speed and focus, preserving the massed percussive instruments' individual voices and characters. There's no lack of continuity between the deep and powerful bass drums and the character of the lighter percussion instruments including blocks and chimes as they all register with the same clarity and incisive ring.


Even the midrange is denser and more there than through my Staxes of old. This is where I heard the most important difference with each and every session. I never became oblivious to how different they were, which is to say that I never began taking things for granted. Where I expected a hear-through ethereal quality, I got a dense presence that I could almost reach out and touch. Here, the 4040II Signature sounded nothing like the Stax of yore. It was here that the Stax system evidenced the presence of tubes. In other words, it was very different and yes, certainly better. There was no downside, preconditioned expectations notwithstanding. Of course, the linearity observed through the bass continued through the midrange as well. That density, that sensation that gave the music an almost physical presence, was the most notable characteristic -no colorations or personality traits vying for attention. In short, midrange
performance was exemplary. Again on the same disc, Gabriel's voice occupies real mass in space, albeit in the listener's head. It's as though he's in there rather than some ghostly apparition. Ditto for the barrage of percussion instruments encircling him.

The treble response is extended, detailed and honest. It'll tell you exactly what's upstream - for better or worse. If there were an outstanding characteristic here, it would be that honesty. You're going to hear it whether you want to or not. Forget sweet romanticism. We're talking garbage in, garbage out. Of course that means that when the signal is good, the portrayal is too. You will want to pay attention to peripherals here. You'll want to provide the 4040II Signature with a good signal and good cables. As I re-read this, it almost appears that such honesty is a bad thing. Hardly. What I'm trying to say is that through the treble, the 4040II Signature will sound every bit as good as your recordings and equipment will permit. That's a good thing. The downside with the Gabriel disc is that it's congested and opaque through the treble and the Signatures do nothing to obscure it. It's the Achilles heel of the disc and if you don't know that, you'll likely blame the Staxes. They convey this fact better than a lot of speakers will.
So cue up something like Joe Jackson's Body And Soul [A&M CD 5000] and from the opening cut, you'll hear the upper registers as cleanly and as clearly as day. You'll hear tremendous air and space around instruments. Where the Gabriel disc proved how adeptly the Stax system masses instruments in a confined space while keeping them sharply delineated from each other, the Jackson disc demonstrates how the 4040II signatures can lay out a soundstage within -- and to some extent beyond -- the confines of your head. And listen to the shimmer of the cymbals at the end of "The Verdict". It's as beautiful as the sense of real acoustic space surrounding the percussion on "Cha Cha Loco" is arresting. "Heart Of Ice" opens with a repeated beat on the hi-hat that when listened to on a system as illuminating as the Stax reveals every component that is frequently glossed over on lesser systems. The initial strike of
the drumstick against the muted brass is something you won't hear on most speakers though it's repeated over and over. The brassy signature of the cymbals as they are briefly opened and allowed to ring and the sound of muted brass-on-brass as the cymbals are again closed was beautifully articulated, repeated over and over throughout the song with fine precession. It's a pity that so few listeners to the disc can hear it the way the Stax system reproduces it. So simple yet so elegant and all presented without any fatiguing edge or splash. Of course there's much more to this instrumental but the point is that the 4040II Signature system will unveil for you meaningful details within the music that are so often glossed over and thereby raise your appreciation of the music to heretofore undiscovered heights.
I should also mention that among all the percussion, vocals and brass were presented with nary a hint of brightness or edge. This means that listening fatigue is vanishing low. It also means that the listener can listen at levels beyond those advisable over the long haul. Where lesser systems will invite restrained volume levels just to control the pain, you can inadvertently find yourself listening to the Stax at exuberant levels without realizing it. Be careful and watch those average SPL. If you're feeling any fatigue at all, you're playing the music way too loud.
Of course, I did have to revisit Pink Floyd's The Wall [C2K 36183] one more time. Okay, maybe twice. Pink Floyd CDs always sound great on headphones. They always make sense and the level of detail achieved by the Stax system always enhances the experience. There's always so much going on. What this Stax system gave me that the old system didn't was really immeasurable. As well as any other disc did, The Wall threw into sharp relief all that I'd been missing before. Deep bass for one. Sometimes purring, often pounding; usually dramatic, always satisfying; the 4040II Signatures have excellent bass with no qualifiers needed. You may not feel it in your gut but you'll feel it in your jaw, which
is actually pretty cool! I can also just about guarantee that most listeners have never observed Roger Waters' vocals with such revealing crystalline clarity before.

Throughout the disc and despite all these years of listening, the 4040II Signature provided some surprises. Check out the bells deeply in the background on "Vera" -- way in the background -- at a volume below the average background noise levels of the home and thus out of reach over speakers. But even that which wasn't completely new was fresh again, like the vocal harmonies at the end of "The Show Must Go On" that were differentiated and fleshed out as I'd never observed them before. The Leslie effect on the keyboards in my right ear on "In The Flesh" was another aspect I don't recall as being so vivid. The list could go on. Suffice to say that the disc was great fun.
As for those Sennheiser HD 580s that stomped my Lambda Pros? The new 4040II Signature actually sounds more like them than they share with the Lambda Pros. But they are not equals. There's no doubt that the Stax is the superior performer where neutrality is concerned. As I said before, the HD580s -- and their HD600 brethren -- have a very smooth and sweet contoured quality. The 580's bass can be thumpier than the Stax. That can be fun but isn't as natural when you need it to be. The 580's treble is sweeter and smoother but neither as extended nor as detailed. The 4040II Signature is a much more detailed system. It eschews syrupy sweetness in favor of life-like timbres and textural honesty. Again, the Stax system isn't about romanticism but authenticity and veracity.
The one area where neither the Grados nor the Sennheisers can touch the Stax system is with soundstaging. It seems that the further away a headset maintains the drivers from the ear, the better the sense of actual space perceived and the more the images are allowed to occur outside of the head. Srajan noted this in his 2002 review of the AKG K-1000s and how they exceeded the performance of even the Stax in this area. Not surprisingly, the AKGs maintain an even greater distance than the Stax. I mentioned earlier the perpendicularity of the Stax drivers to the ear. What I didn't mention are the relatively large drivers of the Stax. Together they do a better job than most of creating and drawing out a
soundstage. While the SR80s and HD 580s provide images that are completely contained within the listener's head, the Stax system does a much better job of preserving and presenting spatial relationships. No, the stage isn't in front of you. It's still primarily in your head. But instruments do regularly break free and can be observed outside the usual inner-head boundaries. Further, while still not naturally in front of the listener, relative positioning upon the stage is maintained to a degree. Frequently elements do arc around the head. Rather than being out in front of the band, the vocalist then is out front and center while the band wraps around the listener toward the rear. In other words, it's the mirror image of what you get with speakers. But when two vocalists for example are on stage, you can clearly and plainly observe one deeper upon that stage than the other.


Of course, life with the Stax system isn't complete perfection. First, those considering the Stax system should know that everybody in proximity will hear your music, just at a reduced level. There's nothing at all to attenuate the level but distance. The earspeakers are dipolar electrostats after all. And of course there's that natural inclination to sing along while wearing headphones which should be avoided at all cost. Oy veh!


From a sonic perspective, the Stax system was very good though not quite perfection. That said, I'm only able to make one real criticism there. As linear and as natural as they are, they are not quite as fluid or organic as the finest speakers. They lack the deft touch of the finest speakers and the ability to detail the finest of brush strokes on the musical canvas. It's not that they are heavy-handed or plodding. Noting like that. I could best analogize by saying that the Stax system operates at 64 bits resolution where the very best and most fluid reproducers are operating at 128. In PhotoShop terms, 250 pixels per inch vs. 300 resolution. As compared to the finest speakers, they sounded ever so slightly coarse where ultra-fine gradations of nuance, musical flow and even micro dynamics were concerned. I thus found my own $17,995/pr Tidal Pianos the more engaging listening experience in that regard. Given the fact that this is the only area where I could wish for something more from the 4040II Signature, I imagine that it's here where the more expensive Stax systems will excel. If they do, they must be one stellar listening experience. In any case, if you're thinking that $17,995 speakers are stiff and possibly unfair competition, you're right. But this is the kind of competition which electrostatic headphones invite. In most ways, they'll stack up better and often surpass less lofty speaker designs in many key areas.
It's more than fair to say that these aren't your father's Stax earspeakers. If you own older Stax models and haven't heard their newer offerings, you may want to. In every way they are better-sounding products. If you're new to Stax and looking for a new relatively private listening experience, I can't recommend more highly that you check out the Stax 4040II Signature system. If at first blush the price of entry looks steep, consider the price of some of the better headphones and also note that most of them will require the use of a dedicated headphone amplifier if you are to achieve anything close to their best. Suddenly the $1,650 for the 4040II Signature system that includes both a stellar headset and a great little tube amplifier doesn't look unreasonable at all, particularly when you consider the inclusion of three separate inputs (one of which is balanced). Such a level of performance and flexibility for such a paltry sum makes them an even better value than my old Lambda Pros and thus one great purchase. As always, the better Stax models may perform better yet but the question is, at what price? Though many might find value there, I have no doubt that for the asking price, most will find the 4040II Signature system plenty good enough. Good enough? Oh yeah... plenty good enough.
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