Today we are talking about the first electrostatic headphone I have done a full review on, the former flagship of Stax Headphones, the SR009S. Stax, a legendary brand in the headphones space, focuses on Electrostatic headphones, and has done for decades. I think it would be fair to say they are the main player in the electrostatic space, which is admittedly a niche within a niche of the headphone hobby. Still, with that being said, they offer unique performance and capabilities, and have a truly die hard following.
For this review, all my listening was done with a HeadAmp Blue Hawaii SE amplifier, a Schitt Yggdrasil GS DAC, and also an iFi Pro iDSD Signature DAC. I mostly want to talk about the headphones themselves in this review, but some mention of amplification had to be made given the electrostatic nature of the headphones. For most reading this review, you likely already know that Electrostatic headphones need dedicated amplifiers or energizers to produce sound, requiring much higher voltages than typical dynamic or planar magnetic headphones. Stax themselves do make their own amplifiers for their headphones, but there is also a thriving DIY community around electrostatic headphone amps, and a few builders of said DIY designs, which sell to the public. The HeadAmp BHSE is one of the more commonly talked about amps in the electrostatic space, though other popular designs do exist. For the SR009S, it is the only amp I had on hand for the review, but is known as a competent model, and I think did the headphones justice.
The SR009S could be considered an evolution of the original SR009, which took the headphone world by storm back when it was released in 2011. The “S” model, was released a few years ago, and as far as I understand, aimed at mitigating some of the complaints that developed around the SR009. I did not have an SR009 on hand for direct comparison, but I have heard it in the past. When the SR009S was released, I think some people were disappointed, as it wasn’t the all new flagship they had hoped for. Of course, at the time or writing this review, that complaint has been rectified with the release of the new SR-X9000, Stax’s new $6200USD flagship headphone. I hope to hear and review that at some point, and June looks like a possible time frame for that review.
However, lets get back to the SR009S, how it sounds, and performs.
The bass of the SR009S was actually better than I had remembered the SR009 being. Electrostatics by their very nature are not exactly renowned for their bass response. With that being said, the 009S did maintain the driver speed and delicacy that Stax does so well. I think for most people, especially if their listening consists of largely jazz or classical music, the stock level of the bass response will be suitable. However, I did experiment with a small boost, about 3db, in the form of a low shelve via EQ. This worked incredibly well, better than I had expected it might. That brought the 009S’s bass level more in line with my personal preferences, and it managed to maintain the speed and quick nature of the driver. Now, in terms of impact, it still wasn’t similar to the Abyss 1266TC, but it was actually better than some other headphones, which surprised me. I think in terms of impact,or “slam” it was similar to the Hifiman Susvara. The bass, in overall terms is quick, some what round sounding, and keeps up even with very complex and fast low end passages. I enjoyed the 009S’s bass more than I was expecting too, but do still prefer some other models for their more visceral sense of the low end.
The mids were actually a bit thicker sounding than I remembered the original 009 being. Certainly not at the level of warmth and thickness the SR007mk2 has, especially in the lower mids, but definitely more so than the original 009. Given that some found the original 009 a bit bright and thin sounding, I can see what Stax was going for with the 009S frequency response. There did seem to be a bit of a peak around the 3k “presence” region, but I found it totally listenable, unlike the Audeze CRBN in this region, which I found overly forward and shouty (review forthcoming on the CRBN.)
In terms of treble, the 009S was more subdued overall than I remember the 009 being. I’m not sure I would say it was dark, but definitely wasn’t as lively and bright as the 009. In terms of treble response, I actually prefer a little bit more energy than the 009S has in its stock tuning, especially in the 7-8khz range. Still, I think this depends on your individual preferences. The upper treble was fine in my opinion, it had enough air, space, and feeling of speed to it. This is certainly one area that Stax seem to excel in. The treble. Perhaps not in terms of tuning (which is personal) but in its overall speed and how quick the driver sounds. I remember the first time I heard the 009, I said it was so quick it was like the notes were tied together. The 009S has a certain sense of this also, but perhaps not as much as the 009, due to the slightly darker tuning.
That brings me to the technical performance of the 009S. Overall, it is a strong performer, similar to its older 009 sibling with slight improvement overall. The overall detail levels are up there with the other high end headphones in this space, though I do think that over the past ten years, the gap has been closed by the more conventional, non electrostatic headphones. It used to be a large chasm in terms of speed and detail, nowadays, much less so. Supposedly the SR-X9000 has improved upon this area again, as you would hope from a new flagship, but I have not yet heard it to do a direct comparison. In terms of dynamics the 009S with its quick nature conveys swings from quiet to loud, both micro and macro very well, but if you are looking for the most impact and slam you can get, you would be better served by other headphones on the market. Sound staging is very natural sounding on the 009S, similar to the Hifiman Susvara in terms of width but with slightly less depth than the Susvara has. Although I still favour a wide sounding soundstage on a pair of headphones, I have come to appreciate more natural sound in terms of width, similar to the Hifiman Susvara and Meze Elite. It is nice to have options, and I appreciate both. With that being said, I’m still not a big fan of smaller soundstages, like the Focal Utopia or perhaps the HD650, but I do understand why some people prefer that approach.
In terms of how easy to drive the 009S is, it is actually quite easy compared to a few other electrostatic headphones that I have done direct comparisons with. The 007mk2 from Stax is vastly more difficult to drive, and requires a good 1/8th (or more) of a turn of the volume knob, to achieve the same volume as the 009S. So far, the 009S is actually the easiest to drive headphone I have tried in the electrostatic category, with the 007mk2, Audeze CRBN, and Hifiman Shangri-La all being more difficult.
In the category of build quality and comfort, the SR009S did well. The overall build quality is not tank like, but it was satisfactory. I think that there is a tradeoff that companies have to try to balance between quality materials that feel sturdy, and the comfort and weight of their headphones. The 009S is an incredibly comfortable headphone, and I never found it feeling too heavy, or causing hotspots on top of my head. It does feel a tiny bit rickety in terms of the build quality and materials, but again, I think that may have been done to reduce weight. Supposedly the new flagship. SR-X9000 improves on the feel and build quality, as you would hope I suppose, at its $6200USD MSRP. Still, I felt the 009S was comparable to a lot of other flagship headphones on the market, and while it wasn’t class leading, it was entirely satisfactory in this area.
In terms of comparisons to other headphones, especially ones that I was able to do directly, the most obvious to start with is the Stax SR007mk2, the 009S’s sibling. The 007mk2 is slightly less comfortable than the 009S, but entirely wearable and much better than some other models on the market. In terms of the frequency response the 007mk2 is warmer, thicker, and darker sounding. If you prefer warm headphones, I would recommend trying the 007mk2 over the 009S. What surprised me was the 007mk2’s technical ability, and how much quality it provides, especially for the prices they are available for on the used market. The 009S does slightly eclipse the 007mk2 in overall technical performance, but perhaps not as much as the gulf in MSRP would suggest. Overall, if you are ok with a slightly brighter response, and want more comfort, go for the 009S. However, if you are looking for a beginner electrostatic headphone, the 007mk2 might be a very good place to start, especially if you find a used model in good condition. One thing to caution is that the 007mk2 is hard to drive, the hardest electrostatic I have tried thus far. Decent amplification is required in my opinion to consider a pair. The 009S is much easier to pair with various amps, and might be worth considering in that sense, vs the 007mk2. It will entirely depend on your amplification situation, and your preferred frequency response, in terms of which I would recommend overall.
The next headphone I compared the 009S to was the Audeze CRBN. I will write more about the CRBN soon in the form of a full review, but I preferred the sound of the 009S overall. The Audeze won in terms of materials and build quality, where it is amongst the best on the market. Still, the 009S had slightly less shout to its frequency response, and after a slight boost in the low end, a similar level of bass. The CRBN had a bit more impact or slam to its low end, but the 009S seemed a bit more airy, ethereal, and “electrostatic-like” in its overall sonic presentation. I preferred the 009S, but YMMV. The CRBN seems to be up some peoples alley, in a very strong way.
Compared to my usual reference, the Abyss 1266TC, the 009S didn’t have the same width in the soundstage, and seemed to be slightly behind in terms of overall detail levels and technical performance. The 009S did have slightly more speed, and again the “ethereal” and “airy” sound vs the more dense and impactful sound of the 1266TC. For me, the 1266TC is still my favourite headphone, but I can absolutely understand why some feel exactly the opposite. The 009S and 1266TC are incredibly different headphones, and excel in different areas. Both are great, I feel.
I think the 009S is for the listener who knows what they are looking for. Perhaps they *know* they prefer the traditional electrostatic airy and ethereal sound. Where the sound seems to just appears from nowhere and floats into your ears. I know that description is perhaps hard to understand, but I think if you have heard high end electrostatic headphones, you might know what I mean. If budget is more of a concern, I would suggest checking out the SR007mk2 (currently $2205USD new) as I think it offers more sound for the money, on the used market in particular. With that being said, if the 009S is in your budget range, it does offer a more technically competent and detailed performance, and I do prefer its tonality over the 007mk2’s tonality. It being slightly less warm, and a bit more treble energy. The 009S is a very comfortable headphone, which lends itself to long listening sessions, and its weight didn’t bother me once.
Overall, I think the 009S is in a bit of a difficult position. It’s not the Stax Flagship, yet it still maintains an MSRP of $4545USD, which is not insignificant. The 007mk2 is clearly the better value proposition, and those who can afford the 009S might also be able to stretch to the price of the flagship SR-X9000. Perhaps the 009S would be better positioned at an MSRP of around about $3400USD? I need to meditate on that question, and consider the market as a whole, especially as the delays around the delivery of the X9000 mean there are not many impressions available about them currently. With all that being said, if you are looking for the sound qualities that electrostatic headphone typically do best, the 009S from Stax is a very worthy consideration, and I could happily listen to a pair all evening long.