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Stax SR-L700 Headphones

It would not be a stretch to call Stax “the first audiophile headphone.” When almost all other full-sized headphones were using dynamic drivers, Stax had already established itself as preeminent by using planar-electrostatic technology. Stax’s technological advantage continued until fairly recently, when the headphone and portable audio business “blew up” into the most vibrant sector of high-performance audio. Unlike in the past when Stax was the only electrostatic option, nowadays audiophiles have their choice of planar designs from many other manufacturers. Obviously Stax noticed the increased competition, and with its SR-009 ($4450) introduced a new electrode structure that refined its original 36-year-old design—and that once again put Stax ahead of its competition.

Unlike most earphones all Stax electrostatic earspeakers use special dedicated amplifiers to drive them. This increases the cost of a Stax system proportionately—with an SRM-007tII ($2150) tube driver unit, the cost of an SR-007 Mk2 system goes up to $4500, while the SR-009 increases to $6600. That puts them among the most expensive headphone systems currently available, and out of the reach of many audiophiles. Stax needed an earspeaker that used the new stator technology in a more affordable package, so it developed the SR-L700 ($1400). Combined with the SRM-007tII, an SR-L700 system runs $3650, and if you opt for a less expensive Stax driver unit, you could put together an SR-L700 system for as little as $2725 by using the SRM-006tS.

I’ve been listening through Stax earspeakers since I got a pair of original Lambda Pros with an SRM-1 driver unit in the early 80s. I currently use a pair of Lambda Pro Nova Signature earspeakers with an SRM-007t driver amp. I also have several pairs of older Stax models including the SR-5, SRX Mk3, and the portable SRS-001 system. In 2013, I reviewed the SRS-4170 system ($1775), which included the SR-407 earspeakers and SRM-006tS amplifier. I found the SRS-4170 system more similar to than different from my older Stax system. Does the new SR-L700 up the ante sonically? Let’s find out.

Tech Tour
The SR-L700 utilizes the same “sound element” developed originally for the flagship SR-009. Stax calls this new ultra-thin polymer material “super engineering plastics.” The new Stax transducer also uses a special electrode scheme, which Stax named MLER (multilayer electrodes). Stax’s explanation on its website for this new technology loses something in the translation from whatever original language it was written in: “While infinite thinness and flatness are required for the fixed electrodes, they simultaneously need to have other characteristics such as low resonance, high transmissivity of sound wave, and so on. The entirely new electrodes have been completed through the unification of metal plates processed with ultra-precision photograph etching using the high technology of heat diffusion combination on the atomic level.” Obviously a dimension can’t be “infinite,” but Stax’s intention was to create a thinner, lighter, stronger diaphragm material coupled with a thinner, lighter, and more powerful electrode array, and it has succeeded on both counts.

Where the SR-L700 differs from the SR-009 and SR-007 is that instead of the new round enclosure featured on those two models, the SR-L700 uses the traditionally shaped Stax Lambda Pro rectangular enclosure, headband, yoke, and earpads. But the SR-L700 enclosure is not the same dimension as previous Lambda models—it’s thicker. The added thickness was necessary to encompass the new electrostatic design.

Stax added several other design changes for the SR-L700, including adopting the click-stop adjustments for the leather headband, making a more robust (but still plastic) yoke, and using new cushion material in the earpads. The permanently attached cable features 6N high-purity annealed-copper wire for core wires, and six silver-plated annealed-copper perimeter wires arranged in a wide parallel structure to lower the overall capacitance.

Setup and Ergonomics
I used the Stax SR-L700 earspeakers with several Stax driver amplifiers including a current-production solid-state Stax SRM-727II and tube SRM-007tII, as well as my own, older units, the SRM-007t and SRM-1 Mk II. Most of my listening was done with these driver amplifiers connected to the Grace m9xx DAC/Pre via a 1/2-meter length of Kimber KCAG.

A manufacturer could assemble the finest-sounding personal transducer ever made and if it doesn’t fit well, it’s sure to be a failure. The Stax Lambda Series has long been considered among the most comfortable headphone designs ever devised, and the SR-L700 continues this tradition. I found the SR-L700 fit me slightly better than my Stax Lambda Pro Nova earspeakers because the SR-L700’s click-stop adjustments (instead of the older friction-fit) insured that the headband’s length didn’t change after every use. I also liked the SR-L700 earpads better—they were slightly thicker and softer. The SR-L700’s clamping force was slightly greater than on the Lambda Pro Novas, but still had less pressure than the majority of headphones. On a scale of 1 to 10, if 1 was no pressure and 10 was getting your ears boxed by a big strong guy, the SR-L700s clock in at a 2.5. You can (and I did) wear them for hours on end with no discomfort.


The SR-L700, like almost all Stax earspeakers, is an open-case design. That means it does nothing to attenuate outside noise from reaching your ears—or from your music reaching the ears of those nearby. For all practical purposes, the SR-L700 is for listening at home in a quiet, private environment. If you need isolation and portability the SR-L700 is not your best option.

The SR-L700’s cable is permanently attached. If you need a longer cable you can purchase extension cables from Stax. I have a Stax 25-foot cable that I’ve owned for more than 20 years, which I occasionally use if I want to pace while listening. It’s still as good today as when I acquired it. I know cable-rolling fans (those audiophiles who like to try third-party cables with their earphones) will be disappointed that they can’t use alternatives to Stax’s stock cable. But the stock cable is so remarkably rugged that even a cable-roller should be content. I have been unable to nick, crimp, twist, or irrevocably bend the cable on my Lambda Pro Nova ear speakers, even after many years of use.

The only aspect of the SR-L700’s physical design that makes me nervous is the plastic yoke that holds the Lambda enclosure in place. It is pretty much the same yoke that Stax has been using for its Lambda Series for the last 36 years. And even on the thinner original Lambda enclosure, the yoke was flimsy and barely adequate. Over the years I have purchased several replacement yokes for my Lambda Pro Nova headphones because they cracked and broke. I suspect that using this same yoke material and design on the SR-L700’s will have similar results. I recommend handling the SR-L700 with extreme care to avoid broken yokes.

The first time that you hear a pair of Stax electrostatic headphones, regardless of model or manufacturing date, the primary impression they make, if distilled down to a single word, is speed. The transient response of a Stax electrostatic design, when compared to a more conventional dynamic driver design, seems “faster,” with less additive distortion stemming from the mechanical action of the driver itself. With its lower mass, an electrostatic diaphragm moves with less physical impedance and once in motion can stop with less electronic damping needed because it has lower mass than a comparable dynamic driver.

After listeners have spent some head-time with a pair of older Stax Lambda headphones, the second thing that many will notice is the ’phones’ unique bass character. The Stax low-frequency presentation has always been airier and faster than other headphone technologies, but many of the earlier Lambda models lacked impact in what I refer to as “the meat and potatoes” upper bass and lower midrange region. The only older Stax model that had enough midbass weight for my tastes was the SR-X Mk 3. The SR-L700 is the first Lambda model that delivers satisfying weight and impact in the lower midrange and upper bass. While it still may not deliver enough low-end impact for serious “bass-head” EDM fans, the SR-L700 definitely offers enough bass to keep anyone who prefers a balanced harmonic presentation happy.

The size and image specificity of the Stax SR-L700 soundstage is dependent on the driver unit that is attached to it. The tube-based SRM-007tII produced the largest and most precisely imaged soundstage, followed closely by the older SRM-007t, which is also tube-based. The smallest and most congested soundstage resulted from the oldest solid-state driver amp, the SRM-1 Mk II. The current-production solid-state SRM-727I’s soundstage and harmonic characteristics were definitely superior to the SRM-1 Mk II’s, but not quite as precise or expansive as the two tube-based driver amps.

Using different driver amplifiers with the SR-L700, I quickly discovered that these earspeakers do “scale up” nicely. By this I mean that when you tether them to a better-performing drive unit the SR-L700’s overall fidelity improves noticeably. As a result, audiophiles who can’t afford the SRM-007tII amplifier will not be hearing the SR-L700’s full sonic capabilities. However, unless you do direct A/B comparisons between amplifiers as I did, I doubt you will find the SR-L700’s sound to be sub-par with any amplifier, including the “lowly” SRM-1 Mk II (which you can find used for around $300). The primary sonic issues with the SRM-1 Mk II are that it had a darker tonal balance and smaller soundstage than other drivers I used with the SR-L700s.

The SR-L700’s new stator design is more efficient than that of the older Lambda design, and at any volume setting the SR-L700s will play louder than the original Lambdas. This increased efficiency came in quite handy with some of my own live concert recordings, which were recorded at lower levels than commercial releases to allow for their wide dynamic range. With the Lambda Pro Novas I had just enough volume using the SRM-007tII turned up all the way, but the SR-L700’s additional sensitivity let me ease up some on the volume knob setting.

During the time I was listening to the Stax SR-L700 I had the new Audience 1+1 V2 speakers installed in my desktop system. Comparing these two seemingly very different transducers, speakers-to-headphones, was enlightening. Both are crossoverless designs that have a more cohesive and well-integrated midrange presentation than a transducer that needs a crossover in its upper midrange (which is where most two-way loudspeakers have their crossovers). But even when used nearfield, my room added some additional midrange energy to the original signal coming from the 1+1 V2 that was absent from the Stax SR-L700’s feed. This illuminated one fundamental truth: If you want to hear how a recording sounds without any room colorations, use headphones. Any loudspeaker, even in a nearfield setup, will interact with the room in ways that will have an audible effect on the overall perceived harmonic balance and presentation. If you need to hear how a recording sounds without room colorations, a pair of SR-L700s is a great way to go.


Unlike days of yore, Stax currently has plenty of competition in the headphone sector. I’ve seen rave reviews of the Abyss electrostatic, and I’ve auditioned them at several audio shows. The Abyss ’phones sounded superb every time I’ve heard them, but they were among the least comfortable premium headphones I’ve used. If you lean forward more than a bit they will come tumbling off your head. For me they were a giant ergonomic fail.

I have not spent much time with the latest flagship models from Audeze (the LCD-4) or HiFiMan (the HE-1000). Both are planar designs that don’t require a dedicated driver amp, making them more portable and flexible than the SR-L700. Both are also more robustly made and should stand up to more abuse successfully than the SR-L700.

Another competitor is the new Sennheiser HD-800S. I own a pair of Sennheiser HD-700 headphones, which are a similar design. The Stax SR-L700s were slightly more comfortable than the HD-700s. The SR-L700s were also sonically less spectacular and less harmonically colored.

If you require a full-sized headphone that delivers a high degree of isolation, none of the Stax open-enclosure designs are going to work for you. But currently none of the other models I’ve mentioned that are in contention for “best” headphone are closed-enclosure designs. As of right now, if isolation is your top priority, you may either have to opt for a custom in-ear monitor or compromise with a headphone that’s not quite as spatially open, harmonically uncolored, or detailed as the Stax SR-L700.

Mike Longworth, who was Martin Guitar’s longtime historian and A&R head, wrote, “The main competition of a new Martin guitar is an old Martin guitar.” The same can be said about Stax earspeakers. When you manufacture products that remain largely unchanged for more than 30 years, that happens. The Stax SR-L700 ranks as the third-best earspeaker in the brand’s line-up. It is also the least expensive earspeaker that uses Stax’s latest stator technology. As such, it is the first new design from Stax that could, due to its combination of lower price and higher performance, lure many longtime Stax owners, such as myself, to replace their older Stax models.

Whether the new SR-L700 will attract first-time Stax buyers is yet to be seen. I suspect that most beginning Stax purchases will be one of the more entry-level packages, such as the very fine SRS-2170 system ($790). But for those audiophiles who want to experience the company’s latest technology, the new SR-L700 is simply the most cost-effective way to arrive at a new level of uncolored Stax sound.


Type: Push-pull, open-back, oval electrostatic headphone
Frequency response: 7Hz–41kHz
Electrostatic capacitance: 110pF (including cable)
Impedance: 145k ohms (including cable, at 10kHz)
Sound pressure sensitivity: 101dB/100V RMS, 1kHz
Maximum sound pressure: 118dB/400Hz
Ear pads: Genuine lamb leather (direct skin contact), high-quality synthetic leather (surrounding portion)
Cable: Silver-coated 6N (99.9999%) OFC parallel 6-strand, low-capacity special wide cable, 2.5m full length
Weight: 0.8 lbs. without cable (1.1 lbs. with cable)
Price: $1400

16617 S. Normandie Ave., Ste. C
Gardena, CA 90247
(310) 327-3913

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