For many decades the name Stax has been synonymous with top quality electrostatic headphones, and many discerning listeners have regarded their top models as among the best, if not the best, headphones presently available. Last year, however, Stax changed the game by releasing a new ultra-rare and ultra-expensive flagship model—the SR-009 electrostatic earspeaker ($5250). To appreciate what a quantum leap into the price/performance stratosphere this represents, consider the fact that Stax’s previous flagship model, the SR-007 Mk2, sells for $2650 (the SR-007 Mk2 will continue in the product line and be sold alongside the SR-009).
The SR-009 is, to the best of my knowledge, the most costly headphone on today’s market, and there is frankly only one thing that can possibly justify its lofty price: performance, performance, and more performance. Does the SR-009 deliver the sonic goods? That’s the question this review will address, but the unequivocal one-word answer is, yes! If any headphone can ever make a $5250 price tag seem warranted, this is the one. Read on to find out why.
I’ve been around electrostatic speakers (and headphones) for most of my adult life, so that I’m very familiar with the technology, but for those of you are new to electrostatic drivers allow me to provide a brief bit of background information that will help explain what makes them special.
Unlike conventional dynamic drivers, electrostats do not use rigid cone or dome-shaped diaphragms, nor do they use voice coil/magnet-driven motor assemblies. Instead, electrostatic drivers use exceedingly light, thin, flexible, conductive, membrane-like diaphragms that are suspended between two fixed, perforated, mesh-like metal panels that Stax simply calls “electrodes” (some manufacturers call them “stators”—hence the term “electrostat”). The only moving part of the driver is the conductive diaphragm, itself, which is incredibly light: in fact, Stax diaphragms are less than 2 microns thick—meaning they have vanishingly low moving mass.
When the earphone is in operation, a continuous bias voltage (580V in Stax designs) is applied to the diaphragm (the voltage is supplied by a purpose-built electrostatic headphone amplifier or “energizer,” as Stax calls its electrostatic amps). In turn, balanced audio signals are applied to the driver’s electrodes, so that one electrode takes on a positive charge while the other takes on a negative charge. As audio signals are applied, the conductive diaphragm is pushed away from one electrode panel and simultaneously attracted toward the other, and vice versa, moving back and forth in precise response to the ebb and flow of the audio signal.
To see a well-illustrated explanation of electrostatic technology in action, click on this link to the Stax web site: http://staxusa.com/Technology.html.
In principle, electrostatic drivers provide several key benefits that no other driver type can fully equal:
• Simplicity: the only moving part in the driver is the diaphragm.
• Precision & Control: the entire surface of the driver is driven, rather than just the center of a cone or the rim of a dome, as in conventional dynamic drivers. This means the whole moving surface of the driver is under the precise control of the audio signal at all times. (The same is also true of planar magnetic drivers.).
• Ultra Low Mass: The very low mass of the electrostatic driver allows terrific transient speed and the ability “turn on a dime,” so to speak. (While planar magnetic drivers are also low in mass, their diaphragms do incorporate conductive metal traces arranged as planar “voice coils,” which do add a little bit of extra mass).
There are really only two perceived drawbacks to electrostatic headphones:
• Specialized Amps Required: Conventional headphone amplifiers are not capable of driving electrostatic headphones. Instead, electrostatic ‘phones require dedicated, purpose built electrostatic headphones amps (or energizers), sourced either from Stax or other amp manufacturers. As a rule, electrostatic amps (or at least ones good enough to be used with the SR-009, tend to be quite expensive).
• Caution - High Voltages Within: By their very nature, electrostatic headphones are high-voltage devices and therefore require amps capable of supplying the requisite bias voltage (again, 580V for Stax headphones), and of supplying high-voltage, balanced-output audio signals. To my knowledge there is absolutely no rational reason to feel anxious or fearful about wearing or using electrostatic ‘phones. Even so, I would concede that some listeners simply do not like the idea of having drivers with hundreds of volts coursing through them positioned just fractions of an inch from their ears.