What, then, is the sound of the SR-009? The answer is that the sound of the Stax will always be an uncannily revealing and nuanced rendition of the signature sound of whatever components you happen use to drive them. Make a change—any change—in your playback system and the SR-009 will immediately report the sonic results (whether for good or ill). No nuance is too small for these ‘phones: they detect and report on every single element in the signal path with almost disarming ease and candor.
During my time with the SR-009, I had the privilege of powering the headphones with three different world-class electrostatic headphones amps: the Woo Audio WES ($5000 - $6000 plus, depending on configuration), the Kevin Gilmore-designed Head Amp Blue Hawaii SE ($5000), and a pre-production prototype of the upcoming Cavalli Audio Liquid Lightning (projected price, $4250). As I listened through the three amps, I was struck by the fact that the apparent “core sound” of the SR-009 changed in distinctive ways every time an amp switch was made. Each of amps offered a compelling, though distinctive take on “state of the art” sound, and what floored me was the almost shocking extent to which the Stax headphone took on the sonic personality of each of the amps (almost as if it became a whole new headphone every time it was fed by a different amp). If ever an audio product were a true sonic “chameleon,” the SR-009 is the one.
Similarly, I tried some very subtle tuning changes in the Playback reference headphone system with the SR-009, such as switching between two slightly difference versions of the same brand of balanced audio interconnect cables I had on hand. Instantly, the SR-009 reported (and in no uncertain terms) the exact sonic differences between the similar but not identical cables, or any other components I substituted within the test system. Where some headphones reveal sonic differences between ancillary components in a general way, the SR-009 reveals the impact of system-level changes in much more detailed, explicit, and precise ways. For this reason, prospective buyers will want to be very careful in selecting components for use with SR-009s. The good news is that these ‘phones will tell you precisely what your system components are doing, but the potentially not-so-good news is that they may expose performance shortcomings you’d prefer not to know about.
Some electrostatic ‘phones I’ve heard exhibit audible limitations in terms of bass power, definition, and depth, and also show a certain reluctance to tackle large-scale dynamic swells with appropriate gusto (both of which are, by the way, areas where today’s finest dynamic and planar magnetic models tend to perform very well). The SR-009, however, shows no such limitations. It can do killer bass with the best of them, and can do the full spectrum of dynamic events—from the subtlest microdynamic shifts in emphasis right on up to full-on moments of orchestral bombast—all in a very convincing way. Indeed, I would say the SR-009 offers state of the art bass performance and dynamic agility.
After careful listening, I have concluded—as has my colleague Tom Martin—that Stax has delivered a milestone headphone in the SR-009. That’s because the SR-009 is qualitatively better than every other headphone we have heard thus face, and this qualitative difference enables the headphone to cross a meaningful threshold in terms of fostering musical involvement. Interestingly, every member of the Playback team who heard the SR-009 independently arrived at the same conclusion: the SR-009 simply draws listeners closer to the heart of the music than any other headphone we have tried.
I won’t tell you the SR-009 “trounces” the other top-tier headphones on the market, because that would be untrue and misleading. It’s just that the SR-009 is a small but worthwhile increment ahead of its competitors, not just in one or two performance areas, but across almost all of the most important areas of performance. This is what sets the Stax headphone apart. In a separate but related Playback review of Woo Audio’s terrific WES electrostatic headphone amp, Tom Martin observed that the benefits of the SR-009 (when powered by a top-shelf amp) include its ability to sound “more transparent than other headphones, … lower in distortion, … and more dynamically accurate.” His comments are spot on; the SR-009 is a true benchmark design.