Stax SR-X9000 - Return to Form

Stax is a company that, for many new to the hobby, is only aspirational. It is the epitome of dedication to the headphone platform. Stax primarily sells electrostatic headphones that require dedicated energizers to power them, so they need a greater investment in source gear than other types of headphones. I expected the SR-007, aka the Omega 2, to be the last headphone I’d buy. When I was finally able to afford an SR-007 system, I was impressed, but not enough to justify keeping it. Ten years later, I've gotten the opportunity to borrow the Omega 3: the SR-X9000. Does it live up to the name?

Build

Build quality is an aspect of Stax headphones that tends to be contentious, as the entry level Lambda lineup is both rather ugly and is made of cheap-feeling plastic. For example, one of the arms on my own SR-L700s snapped during shipment. The higher end Stax, however, are built in a way that overcompensates for the Lambda lineup. I maintain the opinion that the SR-007 is one of the most beautiful headphones in existence, and the build is totally unlike the Lambdas'. While I don't think the SR-X9000 scratches the same itch for me aesthetically, I can't deny it is a well-built frame that looks more like an evolution of the original SR-Omega:

What about the SR-009?

Readers may notice the lack of SR-009 talk. That can be chalked up to the fact that, for some reason, Stax themselves have never referred to the SR-009 as "SR-Omega 3." I do believe this makes sense, as the SR-009 and SR-009S are a departure from the SR-007's and SR-X9000's sound, but I have wondered myself why this was the case. I'm not aware of any official stance regarding this naming, so only assumptions can be made.

Associated Equipment

This SR-X9000 is on loan from a friend, and he graciously also lent me his Cavalli Audio Liquid Lightning MK2, ballast resistor modded Woo WEE, and Bricasti MC1 so the systems I've used for this review are a bit different from my normal chains. I may have also gone a bit overboard with digital in recent months...

HQPlayer (sinc-mg filter) -> Afterdark Rosanna Diretta Network Bridge -> USB Fiber Isolator -> Accurate Audio DIP-B660 DDC -> Metrum Adagio/Bricasti MC1 -> Cavalli Audio Liquid Lightning MK2 or Woo WEE -> Esoteric A100/Kenwood L-07M

Sound

To bury the lede a bit, I really like the SR-X9000, but I've liked it a lot more with the Liquid Lightning MK2 because it seemed to balance out the bit of honky sound I hear due to its elevated center midrange. It was so shockingly noticeable I had to measure it compared to the WEE with my Kenwood L-07Ms, and, perhaps unsurprisingly, the midrange was pretty much the same:

There was some rolloff on both ends measured with the WEE, which is behavior that is in alignment with typical transformers. It may be possible, then, that this could be part of why the difference was noticeable, as the bass and treble are measurably quieter. Presentation of sound was different too: the WEE stages more upfront, potentially contributing to the "honk," while the Liquid Lightning sounds more diffuse, as I'd expect from an electrostatic headphone.

Bass

Electrostatic headphones infamously have a unique bass presentation. Like planar magnetic headphones, they tend to have a (mostly) sealed front volume and can extend quite flat, but most electrostatic headphones I've heard have even softer transients than most planar magnetic headphones I've heard, trading impact and decay for a "faster" sound. The SR-X9000 is no exception, but I do hear a greater sense of impact and decay with the SR-X9000 than I've ever recalled from my SR-007. Ultimately though, I still get the sense that kick drums sound like they're more stuffed than they should be.

Midrange

Midrange is colored, bringing center midrange a little too forward, making both woodwinds and higher pitched voices sound mildly artificial. But I am content with the amount of texture I hear. Some electrostatic headphones like the SR-Lambda Signature, SR-009, and DCA Voce sound a little too lean in the lower midrange for my preference, but the SR-X9000 doesn't have this issue for me. The SR-X9000 doesn't have much pinna gain, which, after manually EQing the gain back, sounds less strange to me.

Treble

Treble is often a pain point for me with electrostatic headphones, which are often quite bright. The SR-X9000 is no exception, but the elevated upper treble is the main source of discomfort for me after about an hour of use. This upper treble boost is used to give a sense of air and space and tends to be a hallmark of the electrostatic sound. I can't say I have many complaints about the low and mid treble, though. While the SR-007 had a bit of treble grain I didn't like, the SR-X9000 does not have this issue.

Measurements

I don't see anything surprising with the measurements–same center mid hump most Stax have, relatively flat bass extension, and somewhat flat pinna gain. The treble does measure as boosted but treble measurements are unreliable.

The ES-1A Problem

In general, the SR-X9000 sounds like a culmination of the lessons learned from the SR-007 and SR-009/S. But there is one thing keeping me from giving the SR-X9000 a glowing recommendation: the ES-Labs ES-1a. The ES-1a is heavily inspired by the original Stax SR-Omega, which positions it as a headphone worth comparing to the SR-X9000. Years before the release of the SR-X9000, the ES-1a was not only one of my favorite electrostatic headphones, but was good enough for me to purchase a pair myself. The first time I heard the SR-X9000, I was reminded of my ES-1a and after measuring two ES-1as, my first impressions don't betray me:

There are some measured differences, but frankly, the difference between the SR-X9000 used with the WEE versus the Liquid Lightning MK2 was more noticeable to me in the areas for which I index. I don't think they sound exactly the same, as I want to say the SR-X9000 presented air and decay slightly closer to my expectations. However, the ES-1a conveys transients with a sort of "bouncy" tactility that gives drums a bit of an edge in accuracy for me.

At the time of writing, the ES-1a sells for around $1,828 USD directly from ES-Labs. This makes the ES-1a $4,372 (before tax) cheaper than a new SR-X9000 from an authorized dealer in the US, which would be enough to get a new Mjolnir Audio KGSSHV and over $1600 to spare.

Of course, there is the argument that the ES-1a is sold as a clone of the original SR-Omega, especially aesthetically, but the ES-1a doesn't seem to pretend to fool anyone into thinking it's actually an SR-Omega. Instead, I see the ES-1a as an homage to the SR-Omega, not unlike some new production watches are designed as homages of other vintage watches of other brands.

Conclusion

The current market feels like a game of chicken, in which manufacturers release mediocre headphones at higher and higher prices to see when the market will finally balk. After being disappointed by so many multi-kilobuck headphones, the SR-X9000 is a breath of fresh air. I believe the SR-X9000 not only succeeds in its goal as a successor to the Omega 2, but does so in a way that balances the fine line between resolution at all costs while still allowing for music to be enjoyable. I can't say the SR-X9000 is worth $6,200 to me knowing that the ES-1a is so close for much less than a third of the price. But, if I were given an unlimited budget to put together a rotation of headphones that I feel are the pinnacle of what we have available today, the SR-X9000 would make that list well before the Sennheiser HE-1, Hifiman Susvara, and a number of other flagship headphones.