Just when you think you can close the book on certain technologies, up comes a new variant which rewrites the rules. I thought things had been quiet on the Stax front simply because there wasn't a lot to add to the peerless Stax SR (Lambda) Signature electrostatic headphones. Little did I know that Hayashi-San had a re-think planned. And if you were around when the Sigmas and then the Lambdas were launched, then you know what a talent he has for creating revolutions in headphone listening. But nothing can prepare you for the Stax SR (Omega). And, no, I'm not pre-disposed to it just because it's named after a brand of wristwatch.
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Unlike its boxy predecessors, the SR sports circular transducer housings, possibly heralding a return to round earpieces. It might just be my imagination, but the new shape – or rather the return to an old shape – offers a more comfortable fit and better encircling of the ear. And, for those too aware of my obsession with timepieces, yes, I prefer round to rectangular or square.
Inside the coffee-coloured housings are electrostatic elements utilising gold-plated copper mesh electrodes of an ultra-fine weave, the material said to resist vibration while limiting reflections back to the 1.5 micron polyester diaphragm. The new diaphragm is some 50% larger than that of the SR and SR, to allow the SR to reproduce '...the lowest conceivable notes'. The housing itself is milled from solid aluminium alloy stock, with the surfaces anodized to increase the hardness and rigidity.
Cursory examination of the SR reveals the familiar, adjustable Stax 'head spring' with its secondary strap to serve as a cushion. The earpieces themselves are 109mm in diameter and 50mm thick, but the size is misleading – as is the weight of 380g minus the cables. Because the cushions slope to follow the shape of the skull and because of the 'double' headpiece, the SR is almost ridiculously comfortable. They neither interfered with my glasses (and for those who accuse me of not listing every damned ingredient in my system, they're wired-framed Armanis with tortoise shell sidepieces and glass lenses), nor did they make my ears feel trapped. My longest listening session ran to three hours non-stop, and it wasn't fatigue which made me break for the day.
Stax has long accepted that cables make a difference, and the company seems to spend as much time engineering a decent cable as they would allow for fashioning other parts of the system. Fitted to the SR is an all-new, six-strand PC-OCC copper lead 1.5 times wider than the previous type to reduce capacitance in each strand by half, thereby reducing signal loss and minimising the interference between each conductor. The system's capacitance (including the cable) is now 110pF, but this isn't really an issue because, unlike conventional headphones, the Staxes can only be driven by dedicated energisers which are tailored to the headphones' specifications. For Stax owners upgrading from older models and with older energisers, the SR works into any Stax energiser with a five-pin 'PRO' socket and 580V PRO bias such as the SRM or SRA amplifiers or the SRD adaptors. The instruction manual does say that you can use the SR into a normal, six-pin outlet, but you should '...expect lower sound levels and somewhat softer sound.' (Stax kindly supplied the tasty SRM-T1S tube energiser for use during the review.)
Other specs for this push-pull electrostatic include an impedance of 145k Ohms at 10kHz, a frequency range of 6-41kHz, a sensitivity of 99dB for 100V RMS at 1kHz and maximum SPLs of 120dB at 400Hz. Anyone exploiting the latter needs his or her head examined. If only to remove the bits of shattered eardrum.
Once you lay eyes on the Paulownia wood (no, I'd never heard of it before, either) box in which the SR is shipped, you know you're in the presence of something which won't work off a personal hi-fi: this is 1695's worth of cans, NOT COUNTING AN ENERGISER! Ahem. To better place this into context, the SRM-T1S energiser I borrowed adds 1095 to the total package cost, though you could get away with as little as 225 for something like the SRD-7SB Mk II and still have a PRO output. If you simply cannot live without SR headphones and must economise elsewhere, 109 for the SRD-6SB entry-level non-PRO energiser is as cheap as it gets, but remember the warning: expect lower levels and a softer – no, make that a murky sound. In relative terms, of course.
As with everything I review, I always try to find the most revealing method for accessing a component's abilities. Usually, that means eliminating as many incidentals from the signal path as possible*; in the case of the SR, it meant running the energiser from a source component rather from pre-amp outputs. Additionally, I used the energiser's balanced rather than its single-ended inputs, driving it directly from the Krell MD10/Reference 64 CD system's cannon sockets and using the energiser's own volume control.
Path Premier's Nigel Crump was absolutely adamant that I run the system in balanced mode straight from the source component, not that I was planning to do otherwise. But I did check to see what the losses were by using single-ended connections or taking the signal from a pre-amp output (balanced or single-ended) instead of off-source. The experience has elicited a caution: Given that any owner of any component will use it in the most appropriate manner for a particular installation, the odds are that many Stax owners will run their energisers off pre-amp outputs, or – depending on the type of energiser – even off the speaker taps. What I would say is that, whatever your system, you must at least audition the SR (or any other headphone with its own energiser) with as direct a set-up as possible. If you don't, then you'll be auditioning a pre-amp as much as you are a pair of headphones. And you really won't know what the SR can do until you hear it in a chain consisting only of source+energiser+headphones.
It's instantaneous. Even before the SRM-T1S was fully warmed up, I knew I was listening to a headphone without equal...and without precedent. Whatever Stax's literature promises, the single most captivating aspect of the SR's performance is its way with the lower registers. I state without any doubt that it's the most realistic, solid, extended and convincing bass I've ever heard from headphones and quite undeniably on a par with bass coming out of proper loudspeakers placed in front of the listener...even though the analogy is weak because the illusion created by loudspeakers differs markedly from the experience offered by headphones.
But you begin to understand why Stax argues that, "...only headphones, which are totally immune to the sonic variations of listening rooms, can serve as a truly universal audio reference standard monitor." You simply cannot fault the thinking, other than to cite the unsociable aspects of headphone use and the somewhat alien nature of hearing sounds inside the head rather than around one's person.
So will you join me in a tiny leap of faith (or suspension of disbelief) and allow me to indulge in headphone listening, which can never be as 'real' as the sound pleced in front of you by loudspeakers? What you gain by trading off the 'spatial reality' of musicians to the front are transparency, a lack of colouration and the near-total removal of unwanted reflections. What's left is the essence of the recording, the pure sound unadulterated by carpets, curtains, furniture, walls, windows or doorways.
Stax's sound, always about as naked as it gets, is bulk information directly injected into your ears. It places as little between you and the music as is possible with recorded media in a playback scenario. And it's disconcerting because there's minimal masking as well as minimal filtering, though the latter is often possibly euphonic and/or desirable in certain instances. So describing the performance is difficult at best.
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Until you've heard the Stax SR, you have only limited knowledge of how fast some transients can be, how texture-free the silences can be. But this applies to many electrostatic headphones. The SR ups the ante by adding or – more precisely – by not restricting the flow of bass. Coupled to this is a dynamic freedom more often associated with horn loudspeakers, so the bass isn't some one-note illusion: the bass moves, it has solidity and mass, it has attack and there are clearly defined leading and trailing edges to every note.
• Read more about STAX headphones here including more STAX reviews.