Stax SR-009 Electrostatic Headphones

Too Long Didn't Read Version: <insert endless stream of superlatives> How can a headphone sound so realistic? How can a headphone so clearly have the best transparency, detail, bass, mids, AND treble by far of any headphone I've used? Ah, one of few headphones with a sound stage and imaging that sounds as if it was trickled down from excellent loudspeakers. As close to perfection as headphones will ever get I think.

If there's any compromise in the audio chain though, or if I have a laid back DAC, the magic is gone for me... the only things I dislike about the SR-009 are the top headband being plastic, and how annoying and expensive it is to get the most out of it, because if you don't get the most out of it (more or less, not saying you need a DIY-T2 amp) then don't bother with it. And you can have a no compromise system but still have a dull sounding SR-009 if something is just a sonic mismatch like the DAC or interconnects.

Full Version:
The Stax SR-009 is a legendary headphone. Tyll's "Comparing World-Class Headphones" review at Innerfidelity opened many peoples' eyes to it, including mine. When I began my hi-fi headphone journey, I just knew the SR-009 was where I had to end up. Since opening this can of worms, I have owned the following open back flagships or former flagships:

- Stax SR-007A
- Audeze LCD-4
- LFF Code-6 (modded HiFiMan HE-6)

On numerous occasions I have also listened to the HiFiMan HE1000, Sennheiser HD 800 S, and Sennheiser HD 800 in quiet environments, and auditioned the Sennheiser HE 1 back when Sennheiser had audition spots for them in NYC. I have also listened to the Abyss AB-1266, entire Audeze LCD fazor lineup, Focal Utopia, and Beyerdynamic T1 Gen 1 in louder environments (not very meaningful listening). Other noteworthy headphones I have owned are listed in my profile.

I really wanted to write this review, more than any other headphone since with the Stax SR-009 and Mjolnir Audio KGSSHV Carbon I have finally reached an end game. With the Stax SR-009, I have perhaps reached the end of my headphone journey (not headphone gear as a whole, but primary at-home listening headphone journey). I don't foresee any major improvements beyond this point, while the SR-009 is a major improvement over every other headphone I have ever owned or listened to... in just about every way.

Before we get started, I must emphasize that high end Stax headphones (SR-007, SR-009, SR-009S) scale more with higher end amplification, DACs, and analog interconnects than any dynamic or planar magnetic headphone. Amp and DAC and interconnects each make a MASSIVE difference. This is an extremely positive review as you're about to see, but it would NOT have been nearly this positive if my DAC was only the Chord Mojo, even with the same amp. Likewise, it wouldn't have been this positive if my amp was a KGSS regardless of DAC. Nor would it have been this positive with cheap generic interconnects.

Going from a KGSS to a KGSSHV Carbon with an SR-007/SR-009/SR-009S makes a bigger difference than going from a Schiit Magni to a HeadAmp GS-X Mk2 with a HiFiMan HE1000 or any Audeze. And going from a Chord Mojo to a Hugo 2 with an excellent Stax system is a gigantic upgrade in every possible way.

Believe it or not, going from cheap generic interconnects like Mediabridge, to Kimber Kable Hero interconnects with this system is a bigger upgrade than most DAC upgrades with ANY non-electrostatic system, and many amp upgrades to. For example, it is a bigger upgrade than going from a Chord Mojo to a Hugo 2 with a Mjolnir Audio Pure BiPolar and Audeze LCD-4 or LFF Code-6, and it is a bigger upgrade than going from a Schiit Lyr 3 to a Mjolnir Audio Pure BiPolar with an Audeze LCD-4. Hard to believe, right?

Another review here says that the SR-009 has less dynamic punch than today's offerings like the Focal Utopia. He mentioned his amp was a KGST (didn't see which DAC). Well, I use a KGSSHV Carbon, I've listened to the Utopia and owned the Audeze LCD-4 with top tier amplification, all of this with a Chord Hugo 2, and I can confirm that statement is a false generalization.

The SR-009 + KGSSHV Carbon + Chord Hugo 2 has the most dynamic punch I've ever heard in a headphone overall, and nothing else comes close. Does this have the most bass impact? Not quite, though more than any open back dynamic headphone I have come across despite not having that annoying mid bass hump. But the attack, transient response, and lightning quick decay, and full bodied/impactful instruments that non-electrostats can only dream of, is what causes this amazing sense of dynamic punch that no other headphone has given me.

But when I substitute my Chord Mojo for the Hugo 2, most of that goes away and indeed the SR-009 starts to lack punch and dynamics. Moral of the story = don't cheap out on any system component!

I can break it down like this:
- Any non-electrostatic headphone system = veiled, muffled artificial headphone experienced
- Chord Mojo + KGSSHV Carbon + Stax SR-009 = Noticeably better than non-electrostats, but still a veiled artificial headphone experience
- Chord Hugo 2 + KGSSHV Carbon + Stax SR-009 = No longer a headphone system but a clear open window into the music (and I'm sure if you swap the Carbon with a KGSS or any Stax amp then you're back to a veiled artificial headphone experience)

Moral of the story is, if you are building a Stax SR-007/SR-009/SR-009S system, don't cheap out on anything. Except perhaps power cables, I don't even hear a difference between generic ones and Pangea ones anyway.
The SR-009 comes in a rather mundane but clearly labeled box. Inside however is a wooden case; not the most protective, I much prefer the Seahorse case ZMF uses or the similar case employed by the Audeze LCD-4 (best included case I have ever come across), heck I also prefer the SR-007's metal case, but this is nice. I store the headphone in it when I don't plan to use it for days. Otherwise, it sits on my Stax stand underneath an electrostatic bag for protection.

Somewhat disappointing in all honesty. The top headband is plastic; one could abuse it and break it. The adjusting slides for the inner headband are also plastic. Surprisingly, the build quality of modern day HiFiMan flagships (formerly HE1000, currently Susvara for planar line and Shangri La for electrostatic) employs a better built headphone body and adjusting slides which are all metal. So... I'd really like these parts to be metal. Or just go with the SR-007's headband.

On the bright side, the inner headband and ear pads are lambskin leather as far as I know. Soft, comfortable, no odd smell, and should last a long time.


The yokes and cups are very solid metal and the cups have a large swivel range. The cable is long and unfortunately not removable, but supposedly of very high quality. While the build quality isn't as solid as I'd like (the SR-007 is also better to me, no plastic), the comfort is top tier. People talk all day long about the HD 800/HD 800 S's comfort, but really the ultimate combination for comfort is adjustable suspension headband with a soft leather inner headband, and large, thick, soft leather ear pads that don't touch your ears at all. Considering this, the SR-009's pads are not very thick, but your ears don't touch anything hard on the inside (they barely touch anything in fact) and the clamp isn't hard so it's alright. Exquisite, flawless comfort.

Adjustment range for the SR-009 could be more. I use it on the largest size and plenty of people have larger heads than me. Poor NBA and NFL players... they won't get to enjoy the SR-009/SR-009S? Though they can afford full range electrostatic loudspeakers so not much is lost for them!

This is the part that matters most and it is where the SR-009 excels the most. The Stax SR-009 is utterly unlike any other headphone I've listened to. Some traces of its excellence exists in the SR-007, but it is a totally different animal. I remain in disbelief to this day how shockingly transparent, detailed, and real it sounds.

I have seen many headphone enthusiasts go through various dynamic and planar magnetic flagships, and never touch Stax. What a mistake. Top tier Stax systems (SR-007, perhaps SR-Omega, and especially SR-009 and SR-009S, powered by at least a well built KGSSHV) make all other headphones sound relatively veiled/muffled and fake. Almost like the others are toys. This is coming from someone who at least anticipated favoring a planar magnetic headphone for rap, but no, I ended up favoring the SR-009 for every genre and it's not even close at all. Line up every headphone I've owned, and I would never reach for another if my goal was musical enjoyment. Only the SR-009. Granted, I never had a beefy enough amplifier for my SR-007A (only a China clone KGSS fixed up by Birgir).

Compared to all non-electrostatic headphone systems, the SR-009 + KGSSHV Carbon or Grounded Grid or Blue Hawaii SE or Megatron or DIY-T2 (and probably a regular KGSSHV as well but to a lesser extent) will reveal MANY new sounds in almost all music that other headphone systems are not good enough to reveal. This is one of the most incredible attributes about the SR-009. The transparency is just almost unrivaled; as I said, almost all other headphones are veiled in comparison, including all dynamics and planars

The SR-009 with a good enough amp will "take you there" and I am convinced only an electrostatic system can do this, since no planar or dynamic system can. Not the Focal Utopia. Nothing from Sennheiser, no HiFiMan planar (and I personally doubt their electrostats too), nor Audeze. They don't come close whatsoever.


It's actually difficult to describe the SR-009's sound signature. You will see people call it very neutral, or perhaps a bit bright, but that's misleading. The sound signature is totally unlike any non-electrostatic headphone. Contrary to what I see written I do NOT believe it is a poor matchup for bad recordings/poorly mastered music. I think the SR-009 makes ALL music sound better, whether vinyl or digital, great quality or not. For crappy MP3s it still reveals sounds I never heard before, and good ones at that, while making the music more transparent and realistic than ever. Such that the only other headphones I have any measurable interest in listening to are the SR-009S and to a much lesser degree SR-Omega (mostly curiosity since I'm entirely convinced the SR-009 and SR-009S rule over all).

So I will describe the sound signature in a nutshell as... mostly neutral but with an upward tilt, wonderfully extended in both directions (spoiler alert: the best bass, mids, AND treble of any headphone I've listened to, and remember I've owned the Audeze LCD-4 and have experience with all kinds), full bodied beyond what any non-electrostatic headphone can achieve, impactful with phenomenal spatialization and sound stage and imaging, the fastest headphone I've ever listened to by far (most realistic decay and transient response I've encountered) which combined with the very impressive bass slam and unmatched treble performance is why I find it has the most dynamic punch of any headphone system I have used.

To me the SR-009 is upward tilted in a way that allows its upper frequencies to create a clear transparent window into the music like nothing I've ever heard before, and this is without recessing any of the lower frequencies. You have not heard full bodied headphone treble worthy of being called authentic unless you've listened to a properly driven top tier Stax headphone.

A well driven SR-009 creates so much more body, weight, impact to nearly every single instrument in existence, compared to all non-electrostatic headphones. The only exceptions are certain drums which the best planars like the LCD-4 can match or surpass in impact, and match in body/weight. But the SR-009's bass is far more transparent and detailed than any planar, such that I prefer its bass to any planar by clear margins.

Every frequency range, from sub-bass to upper treble and everything in between, is FAR more transparent and detailed and realistic than every headphone I have heard to date (though again, never properly amped my SR-007A). Of all headphones I've listened to, only the SR-009 has perfected the upper mids to lower treble transition. This perfection right here, this frequency range, is responsible for making nearly every other headphone sound veiled and fake and even toyish in comparison, especially non-electrostats.


But the SR-009, SR-009S, and SR-007 are some of the most amp dependent headphones out there. For example, I have also listened to the SR-009 out of the Woo Audio WES, and it was just veiled and obscured compared to a Blue Hawaii SE or KGSSHV Carbon. To get the most out of these headphones, you do need a very expensive amplifier like my Mjolnir Audio KGSSHV Carbon. But even then, my SR-007A + KGSS was more transparent than any non-electrostatic headphone, with noticeably more full bodied and realistic treble than any non-electrostatic headphone, but still absolutely nothing compared to how it sounds with a top tier amp (I have used the SR-007Mk1 with a HeadAmp Blue Hawaii SE on several occasions).

But when I use the Chord Mojo as the DAC instead of the Hugo 2, a LOT of this magic is gone. Much of that transparency, resolution, impact, airiness, sound stage, and imaging gets flushed down the drain. It's still far more transparent than any non-electrostatic system I've listened to but yeah... this is kind of lame haha.

Let's try to break it down and get more specific here.

Bass
The most breathtakingly convincing bass presentation I have ever heard in a headphone. Remember, I've owned the Audeze LCD-4. Compared to that, the SR-009's bass transparency and detail are as if it opens up a window, revealing a new dimension to bass that not even the best planars can reveal.

The LCD-4 does have much heavier bass presence creating a thicker sound which some might prefer (bass is always distinctly present during all sounds), no doubt about that, and it can slam a bit harder as well, and it extends deeper, but it's still missing a dimension of clarity and details compared to the SR-009's bass. Percussive instruments even sound so much more real on the SR-009 than any planar. One of the most impressive attributes of bass performance with the SR-009 + KGSSHV Carbon is the portrayal of very fast drums on heavy metal songs. The SR-009 just annihilates all non-electrostatic headphone systems here.

Using the bass sweep test at this website, the SR-009 only seems to extend down to around 20 Hz while great planars can go down to around 10 Hz, but that's no big deal in practice since music almost never goes this deep. Believe me, I care a ton for bass extension. I listen to rap and heavy rock and metal, and the SR-009's bass is by far my favorite of any headphone I've listened to. It even has more bass slam than most headphones, more than my previous LFF Code-6 (modded HiFiMan HE-6), more than the HE1000/HE1000 V2 so probably more than any HiFiMan headphone that ever existed for reference.

There is a stereotype about electrostatic headphones having less bass than dynamic headphones or something. The main source for this is that dynamic headphones naturally have a mid-bass hump... as well as sub-bass rolloff which is another story. Well, I cannot name a single dynamic open back headphone with more bass slam than the SR-009 on an amp like the KGSSHV Carbon, nor can I name a single dynamic open back headphone with a single advantage in bass performance vs the SR-009. Then again, the only dynamic open back headphones I've listened to with any advantage over the SR-009 are the Sennheiser HD 800 and HD 800 S in imaging performance, but the SR-009 is close enough for me. But I digress.

Mids
Magical. Vocalists are super clear and brought to the forefront, but at the same time you can't help but notice incredible sound staging and imaging, so many layers to music, perfect instrument separation.

The most impressive thing about the mids to me is the body, weight, and impact to every instrument. Of course this isn't limited to the mids, but every instrument in every frequency range has a fullness and impact to it that I've never heard before. I've never heard such full, clear/transparent, and real sounding strings or pianos or horns before for example. Not even close. These instruments and many others sound tiny, veiled, obscured, and fake in comparison, and again the difference is massive.

There is a slight upper mid range hump visible on frequency graphs, which to my ears manifests as a slight upward tilt that gives more body/weight/fullness to the upper mids to treble transition area, where so many headphones sound weak/frail and fake in comparison. But this upward tilt isn't to everyone's preference and I am really curious how the SR-009S sounds which supposedly doesn't have this. But as it stands, I have no issue with any mid range region.

Treble
Of all frequency regions, the SR-009's treble is the most impressive to me, because of how much better its treble is than every other headphone system I've owned. It doesn't overshadow the rest of the spectrum, but the SR-009's treble doesn't hold back at all... yet it is the cleanest, clearest, most full bodied, most realistic treble I've ever heard by far and is largely responsible for this headphone sounding so transparent, detailed, and real. Every non-electrostatic headphone's treble sounds so thin and one note compared to this. Words really do not suffice, you have to hear a properly driven SR-009 in a quiet environment. This improvement will jump right out at you immediately.

Likewise, the upper mids to lower treble transition is like no other headphone I've heard before. It creates a whole new dimension of realism, transparency, detail. I've also never heard such "airy" sound from a headphone before. This airy factor seems to improve imaging and perceived realism significantly.

I was surprised to 'only' hear the SR-009's treble extend to 20 KHz in the treble sweep test located at this website. My previous LFF Code-6 (modded HiFiMan HE-6) reached 21 KHz, so it's not my ears. So the Code-6 has the most treble extension I've ever heard, SR-009 is #2. But in practice this is meaningless... what music goes beyond 20 KHz?

With all of that being said, the SR-009 will always be too upper mid/treble forward for some. Some will always prefer a thick, laid back sound like the LCD-4 or better yet ZMF planars. But for all you Focal Utopia, Sennheiser HD 800/HD 800 S, AKG K812, Beyerdynamic T1/T1 Gen 2, and HiFiMan HE-6 lovers, the SR-009 or SR-009S is your ultimate headphone most likely. It beats all of those in nearly every area, the exceptions being imaging versus the Sennheisers, but the SR-009 images so impressively anyway and if you really want more, I'd suggest loudspeakers. If you want neutrality and realism above all, the SR-009 or SR-009S is your ultimate headphone.

Sound Stage/Imaging
Superb width, depth, and height. Best in each category of any headphone I've owned by far. Imaging is precise and very natural, also the best of any headphone I've owned by far. Most importantly is the flawless instrument separation and sense of layering; no sound overlaps where it shouldn't, which is standard practice for elite open back headphones. But even then, the SR-009's instrument separation clearly surpasses every other headphone I've owned, which combined with the sound stage makes for very immersive listening.

The SR-009's most impressive sound stage dimension is its depth. You're going to need something like the Sennheiser HD 800 / HD 800 S, maybe the Abyss Phi/Phi CC, and of course the Stax SR-009S to compete here, and you will need something like the AKG K1000/MySphere (and maybe the Stax SR-Sigmas?) to win here.

When comparing the Stax SR-009 + Mjolnir Audio KGSSHV Carbon to the Audeze LCD-4 + Mjolnir Audio Pure BiPolar setup, the latter sounds veiled, unrefined, two dimensional, not detailed, with a flat sound stage and poor imprecise imaging in comparison, plus the LCD-4's horrible lower treble dips ruin vocals, pianos, and many other sounds.

But the LCD-4 does sound "thicker" in the traditional sense: there is considerably more bass presence, creating more emphasis on the lower frequencies. The LCD-4's bass is always present, when it's not called for then you can still hear/feel it waiting in the background waiting to explode, and when it explodes there's more of it. More... but of considerably lower quality than that of the SR-009.

I really was not expecting the Stax SR-009's bass to far outperform that of the Audeze LCD-4. While the LCD-4 has more quantity, it's two dimensional in comparison while the SR-009's transparency and resolution brings out tons of hidden sounds from the bass region... and every other region, and the bass texture is so much more real. The only real concrete advantages the LCD-4 has are deeper bass extension and stronger sub-bass presence which are fairly minor, then on top of that subjectively some people will prefer the added bass presence of the LCD-4.

There's no way the SR-009 should cost less than the LCD-4 if you ask me. The LCD-4 has far more treble woes than various good $500-1,000 headphones, making it sound more artificial in comparison. And it cannot compete with the SR-009 technically. If people were to blind test both of these systems, I suspect most if not all would guess that the SR-009 is the much more expensive headphone. I wish I could've blind tested them, but I returned the LCD-4 a while ago.


Compared to the LFF Code-6 + Mjolnir Audio Pure BiPolar, the Code-6/HE-6 is clearly like a much lower end version of the SR-009. The Code-6 has, in comparison, soft muddy bass, weak sound stage and imaging, thin mids, thin treble that lacks airiness, lack of detail and transparency. Definitely not the same level.

The Stax SR-009 and KGSSHV Carbon is the biggest headphone upgrade I have ever made. Going from the Audeze LCD-4 and LFF Code-6 (and I would say the Sennheiser HD 800/HD 800 S and Focal Utopia as well based on my experience with those) to the SR-009 with an elite amp is a bigger upgrade than when I went from a Cooler Master 5.1 surround headset to an Audio Technica ATH-A900X and Beyerdynamic DT 880 Pro and AKG K7XX.

I would say it's a bigger upgrade than going from the Sennheiser HD 598 to the HD 800/HD 800 S, because the Stax will reveal a greater amount of new sounds and detail than that upgrade, and it will offer a bigger leap in transparency and authentic full bodied portrayal of all instruments.

Not much left for me to say. The SR-009 when driven by an excellent amplifier such as the Mjolnir Audio KGSSHV Carbon completely, totally outclasses all non-electrostatic headphones in transparency, realism, and detail. It will introduce new dimensions, new sounds that were always hiding in the music, to every frequency range in nearly every song. I did not think this was possible. It seriously makes all non-electrostatic headphones sound "Low-Fi" in comparison, at least when pairing the SR-009 with a capable amplifier such as the KGSSHV Carbon. An SR-009 with a KGSS or SRM-353X, or a Chord Mojo tier DAC (regardless of amp) will NOT do this.

Some people have written that the SR-009 is too analytical, almost too technically perfect, and lacks euphoric character. For me, this is absolutely not the case. Since no headphone connects me to the music as much as the SR-009 (but I need to try the SR-009S), that makes the SR-009 by far the most euphoric headphone to me. All other headphones are too veiled and fake sounding to me, while the SR-009 with a proper amplifier connects me to the music directly with no obstacles in the way.

I broke this review down into the following sound sections above: bass, mids, treble, and sound stage/imaging, and the SR-009 clearly bests every headphone I've owned in ALL of those categories, as well as in transparency obviously and also detail retrieval. Yeah... hands down the single best in every category. I wasn't even expecting this. I was expecting the LCD-4's bass to outright beat the SR-009 but that's not even close to what really occurs. The SR-009's bass clearly wins in quality, it just has less quantity (but still a lot of quantity, more than any open back dynamic headphone I have used).

Thanks to the SR-009 + KGSSHV Carbon combo, I'm selling off most of my headphone gear and sailing off into the sunset (UPDATE years later: obviously my journey didn't really end here, but with loudspeakers). I'll remain interested in new amps designed by Kevin Gilmore (or existing designs further developed, e.g. KGSSHV Carbon Nanotube).

Any improvement beyond this will be so insignificant I think, as far as headphones go. No other flagship or former flagship headphone fully scratches my itch for better sound, but the SR-009 and KGSSHV Carbon and Chord Hugo 2 combination plus good analog interconnects does (if I substitute cheap interconnects it certainly does not. This combo is just too superior to all the flagship stuff I've owned or listened to in the past.

When the Stax SR-009 first came out, there wasn't anything on the market really capable of matching its resolution and clarity. Give or take 7 years later, there still isn't really anything on the market that can match the detailed, transparent sonic image only electrostats can provide
In terms of positives, the SR-009 are still the most transparent headphones on the market. I've always hated phrases that describe transparency, "it sounds like an open window to the music" or "just the music" due to their vagueness. Whenever reading comments such as those on the SR-009 I always wondered what it was that my headphones weren't doing right. Was it the sound signature that was limiting my open window? Maybe my headphones lack of transient speed? The goal of ultimate transparency is to have the listener forget that he/she is wearing headphones, I personally believe that the only real way to understand transparency is to hear it, and believe it or not, it's not exactly what everyone goes for. Transparency implies an ultra-revealing, and natural sonic image, and thus can be tiring. Constantly having an ultra low distortion microscopic view into your music can wear you out. Every headphone seems to have a flavor except for the SR-009. It offers perfection in speed, transients, decay, resolution and realism, but lacks flavor and coloration.

Just about every headphone I've been through, I've always found flaws in its sonic signature that lacked the "technical" 5% to give a 100% ideal musical experience. Even the HD800 (with SDR modifications) I found to be somewhat lacking in ultimate speed, and only now owning the SR-009s, transparency have I realized this. Electrostats are on another plane of sonic existence compared to everything, they have it and everything else doesn't really have it (yet). The SR-009s have the speed to resolve just about anything the song offers due to their ultra-fine film diaphragm. However it seems that these ultra fine diaphragms have their fair share of weaknesses

Mainly Dynamics...

Head splitting, ear shattering, and explosive aren't the kind of phrases you'd use to describe the SR-009. It's sound is more like clean, fast, and effortless, yet that sound is somewhat physically 2-dimensional. They lack the ability of headphones such as the Utopia to reach out and tickle your ears. To burst out of the mold the diaphragm provides. which leads me to ask...

Where's the meat?

The sound of the SR-009 is like eating the most delicious meal in the world, but not having it fill you. The SR-009 lacks that filling euphoria that you get when you bite into a thick steak (e.g. Focal Utopia, Audeze anything). There's a whole meal after the meal, namely when your sitting on your couch after dinner recuperating and watching Sunday night football that the SR-009s seem to lack, it leaves you hungry. I'm not saying that they're thin or un-involving, their tonal balance prevents that, however compared to today's offerings, the SR-009 lack big boy dynamics, which seems to be a common characteristic in these new gen thin film diaphragms (Hifiman HE-1000). While the HE-1000 is just polite and smooth, the SR-009 is a straight edge of a headphone that still remains sonically involving due to it's sheer resolving capabilities.

Now onto Sound
Signature

Basically perfect, the SR-009 has the most linear SS I've ever heard, especially the treble. The massive dip at 6k is perfect, prevent harshness and sibilance (which plagued the HD800). It naturally resolving quality leave no vagueness in the treble either. The bass is extremely linear as well (just look at the graphs, it's like fiction). It's an extremely clean sounding bass that reaches very low, though not as low as Audese's offerings, but they go toe to toe with any other dynamic headphone. Bass resolution is also ungodly impressive. The SR-009 are like the CIA's version of Photoshop, where they can zoom into anything and maintain resolution.

SoundStaging and Imaging

Here's where they lose to the other World's best headphone. The HD800's bests them in soundstage width, and overall imaging. The HD800s are the closest thing to speakers, whereas the SR-009s are still blatantly headphones (which is fine, it's why you still listen to headphones). The sound is still in your head with the SR-009. The imaging of the SR-009 however is very impressive due to its speed, though not as much as the HD800s, which have that extra bit of space allowing more precise placements of various sounds. However, I do feel like the SR-009s do a better job in the sizing of the instruments and tones. I felt that the HD800s made tone and instruments larger then they actually were, whereas the SR-009 has more accurate sizing (not placement though). The Utopia's also do a good job of this, and are actually better then the SR-009s at this.

My Equipment and Biases

I run the SR-009s through a KGST, but have heard them through the Blue Hawaii, and various other DIY efforts. Now you can criticize me (and my 5k setup) for not having the last word in amping the SR-009s, but I highly doubt that they would ever have better dynamics then the Utopia, the Audeze's, or even the HD800 (which did actually have greater slam) on a well driven amp. The SR-009 was never design to have amazing slam or powerful dynamics, and while it has good dynamics, they just can't match traditional dynamic headphones in this category. It was never a focus to begin with, and that quality is very apparent when listening to the SR-009s

Conclusion

It all depends on what your looking for. If you want the clearest window into music, estats my friend, but you must be willing to trade the dynamics and low end slam for it.

I own the Stax SR-009 along with the SRM-007tII since February 2013 and I am still very happy with the purchase.

I want to say, that I use the SRM-007tII as the amplifiier and my source is an AVM Audio CD 5.2 Evolution CD Player, which I also use for streaming with my Macbook. I have a set of Kimble 1126 XLR cables, Fisch Audiotechnik Performance 2 main plugs and a MFE powerboard. So I can say, that I have my fair share of High Fidelity at its price.

That being said, let me state, that, counting the SR-5 Gold, the Signature I, II and for a couple of weeks a pair of SR-007, this is my fifth Stax set in a row. I haven't compared Stax headphones/earspeakers with competitors for more than 10 years. In that regard, I am not objective, nor do I claim to be.

The set comes in a wooden box, which seems appropriate considering a 5'000 € earspeakers set.

The SR 009 has a very natural sound. I can't complain about the basses, maybe they could be stronger. Perhaps I am just used to the sound of a Stax. In general, the instruments are very clearly separated and balanced (I hear instrumental Free Jazz, Improvised Music and Post Bebop). The musical proponents more often than not go to the limits of the their respective instruments and beyond them, which is well heard through the SR-009 set. At least I couldn't detect any overstated mids or highs.

The set is a very easy to wear, the leather pads are well crafted and a jiy to wear (I clean them with a wet drying towel from time to time). I am worrying that the Stax energizer, which is not a subject here, can get very hot after a couple of hours of listening; I am just saying.

As I have said, at the beginning, I had the SR-007 for some time. But honestly, I always missed something and accordingly upgraded to the SR-009. And believe me, it was and is worth the difference in price and sound. The SR-009 looks much better (the mix of used colors and materials are for favorable), sounds much clearer and more balanced. If you can spend so much money and willing to do so, the SR-009 is a serious shoe in.

I have read in other forums, that stereo devices that much expensive are not worth the "admission". I can't totally disagree, as everyone has to figure out, if he or she can and is willing to spent that much money for a stereo equipment.

All I can share here is, that the Stax was and is a pleasure to use and hear. In many ways, it has opened a whole new universe of listening experience to me. Each Stax set had its time and now it is the SR-009 and the SRM-007tII, which offer a great deal.

As I have pointed out before in my review of the Stax SR L700, electrostatics and Stax are the latest port of call in my journey of discovery in the world of audio bliss. I recall it was April or May 2015 when Spkrs01 opened the door to the intriguing world of Stax. Prior to this, Stax was only something that I heard about occasionally, but always referred to in hushed tones of deference, especially when the subject was the venerable Stax SR-009. Everyone swore blind that it is the best headphone in current production, bar none. Pity about the lack of bass but what ethereal sonics: so the conventional wisdom went. Admittedly, when I heard the SR-009 off a Stax amp, this seemed to be borne out – great atmospheric trebles and very quick, but where did the bass go?!
In this journey into Stax territory, two persons get honourable mention as my trusted and patient guides: Spkrs01 and AnakChan. No question was too trivial or frivolous. Poor Spkrs01, in particular, bears the brunt of my insatiable curiosity.
 
I have since learned that fed sufficient driving power, the SR-009 is peerless in its transparency, details and texture. While it will never match the visceral bass of the Abyss, it possessed a bass that was detailed and layered. And I would never accuse the SR-009 of sounding “thin” when properly set up and driven.
 
I started off with the SR-009 and SR-007 Mk1. Since then I have added the SR-007 Mk2 and the SR L700 to the stable of Stax cans. On an aside, I have a tidy little collection of non-electrostatic cans comprising most of the top tier Grados, the LCD 2 & 3, HD800, Hifiman HE-6, HE-5LE, HE-560, HE-500, HE-1000, Fostex TH900, AKG K702 & K812, and the Final Sonorous X and the Abyss.
 
 
Home Desktop Stax Set Up
 
The Stax setup  starts with an Auralic Aries (with external linear PSU), connected via a Audiquest Diamond USB 3 cable to a Bricasti M1 DAC and then a pair of Tralucent Uber balanced interconnects to the Cavalli Liquid Lightning 2, and then pass through to the VAW 8PS via a pair of Toxic Cables Silver Venom balanced interconnects. Power cord for the DAC and the Liquid Lightning 2 is a Tralucent Uber power cord, while power to the VAW 8PS is supplied by a Tralucent Silver/Gold power cord. Power to the components of the desktop rig and sources is fed through an Isotek Aquarus and all the power cords use US plugs. Mains power is fed to the Isotek Aquarius via a Tralucent Uber power cord.
 
My Synology DS 414 and a Seagate Backup Plus HDD (connected directly via USB to the Aries) are powered by the new Plixir Elite BDC Power Supply kindly customized for me by James Soh of Sound Affairs in Singapore. James had also helpfully suggested that I run a separate switch for the audio components away from the wifi access point. The switch is also powered by the Plixir Elite BDC Power Supply that James customized for me. The Aries and the Synology DS414 NAS are connected via the dedicated switch by a pair of Ranko Acoustics OCC audio LAN cables.
 
 
Build Quality
 
The build quality of the SR-009 is really top notch. Even my personal preference for the headband of the SR-007 doesn’t detract from this.
 
 
Comfort and Isolation
 
The round ear cups of the SR-009 sit very comfortably  over my ears. The use of lambskin for the earpads help in that respect. The other thing that helps is the light clamping force, while being sufficiently firm.  At the same time, it is amazingly light in my hand or on my head. It puts some of the planar magnetics like the Audezes and the older Hifiman to shame in this area.
The Stax SR-009 is an open can and isolation practically non-existent. The fact that I can hear almost every word the Mrs says when I have them on is testament to that.
 
 
Music Genres
 
My digital music collection extends about 12-15 TB. In my collection, you will find most genres from classical music all the way to acoustic vocals, modern jazz vocals and mandopop music. I even do rock and pop.
 
I wish I could say that the SR-009 is incredibly versatile and can handle anything I throw at it with finesse and aplomb. That would be music to the ears of those who complain about how much it costs. Well, I am not going to say that. However, I will say that it does classical music, jazz , mandopop and vocals very well. In fact, no other can does female vocals like the Stax Omegas, in particular the SR-009. I still recall Spkrs01 warning me that one may pee in one’s pants listening to the magical quality of female vocals on the SR-009.
 
One word of caution: the SR-009 is very transparent – if you feed it badly recorded music, it will chew it up and spit it back in your face. This is no shy retiring ice princess. If you music sucks, it will let it all through, magnified, back to you.
 
 
Sound Quality
 
I own the HD800 and I have it paired with a crystal piccolino balanced cable. I also thought it was the last word on refinement and transparency. At least until I heard the Stax SR-009. I recall that I used to wince now and then at certain sibilance in vocals by Alison Krauss in her plaintive and lilting voice beloved by Bluegrass aficionados. At other times, there would be certain hard edges in the trebles. 
 
Well, with the SR-009, there are no such issues to fix. Ms Krauss sings with the voice of an angel as she is.  The trebles on the SR-009 are extended and yet are clear and pristine with nary a harsh edge. While I am not a big fan of treble extension as some other hobbyists, this smooth and flawless treble extension can be very useful if you listen to someone like Sarah Brightman…
 
The mids of the SR-009 are lethal: other than the possibility of incontinence, you get lulled in this state of swooning when you listen to lovely voices belonging to Anita Mui, Sandy Lam, Stacey Kent, Diana Krall and their ilk. The nuances, inflection of their voices and emoting of their heart felt feelings can be almost unbearable.  With regard to the music generally, the SR-009 conveys great texture and timbre. The soundstage is wide as it is dense, layered and deep.
 
The bass of the SR-009 is the one area which attracts a lot of adverse comments. Like I had said earlier, do not expect this to be like the Abyss. Nothing will come close to the Abyss for its visceral bass. Yet, the SR-009 does have a deep and tight bass. Whenever I play the album, Audiophile Percussions by Gabrielle Roth and the Mirrors, which features 9 divine tracks exploring the various types of percussion instruments on the SR-009, it leaves me picking up my jaw from the floor. I defy anyone to listen to that album on the SR-009 off a TOTL electrostatic amp and say thereafter that the SR-009 has no bass… What you will also notice when you play this album is how quick the SR-009 is.
 
At the end of the day, the SR-009 is a very unusual can. It is very transparent. It is quick. It is smooth, refined and nuanced. However, it will hiss and spit at you if you dare to try to insult it by playing crappy music.
 
 
Pairing
 
The SR-009 does appreciate the driving power of the Cavalli LL2 and VAW 8PS. It is so transparent that the differences in character between my two amps are easily apparent: the slightly more laid presentation of the LL2 in mid concert hall, while the VAW is more immediate in its presentation where you are seated in the first few rows of the same concert hall. Both pairings are absolute joy and very musical. This is very important to me. I fear that I am not quite an audiophile who listens to my gear: what I want and demand from my rig is that I should enjoy the music and be moved by its presentation.
 
 
Conclusion
 
Thus far, I am happy to say that, despite Spkrs01’s promise, I have yet to suffer any incontinence while listening to my favourite female singers, like Diana Krall or Sandy Lam, on the SR-009. However, when I feed the rig well recorded and mastered music, whether red book or high res, the SR-009 is peerless in moving me. It doesn’t get any better than this.

the first time I tried an electrostatic headphones I did not believe what I heard: the amount of details the Stax L700 delivered made my literally cry. the next one was the SR-009...
 
i tried them with the Stax SRM-727 II,

SRM-007tII​

 and a German made Mal Valve Headamp (mark II?).
 
 
design
i would not say that these are the best looking headphones on the market, however, I still like the way they look a lot. it does feel premium. the headbands are well made and it fits to most heads. the pads are soft.
 
comfort
I personally find the Stax L700 more comfortable, however, the SR-009 is also very comfortable. and it is lightweight. especially compared to the Audeze headphones.
 
soundstage
these cans have a smaller soundstage than the Sennheiser hd800, and it is not that much in front of you as with the hd800, rather next and behind you, but the quality of the soundstage is better with the Stax. The hd800 is almost too loose, too unorganised, too wide. The sr-009's soundstage makes sense. everything is at its right place on all the three axis.
 
imaging
just as the soundstage, the imaging is fantastic. everything has its own aura.
 
details
this is where these electrostatic headphones are waaaay ahead of any other headphones (I haven't tried the 2016 Orpheus though). I even tried them with a 320kbps mp3 track too see how they react and I never thought that such a poor source has so much detail (information) embedded. There is such a big discussion about music compression, however, I believe that there are barely any headphones out there that can reveal all the details even in a poor audio source... 
 
highs
the highs sound soo true and so amazingly clear and detailed, it is hard to describe.
 
mids
the same goes for the mids. they are amazing.
 
lows
this is probably the only point where I can complain a bit. though they are well extended, I think that the average quality of the lows are falling behind the other frequencies. I think they could be more detailed and more articulated. Sometimes I had the impression that these cans don't care much about the lows that much. sometimes they felt "empty".
 
speed
these cans are extremely fast. almost too fast.  
 
general characteristic
they are bright and for my taste too bright. So I had to try them with different cube amps until I reached the point where they were soft enough for my ears (the Stax 

SRM-007tII​

 cube driver failed to soften them enough but the Mal Valve was able to do it). The Stax SRM-727 II made them more organised, more "on the spot", but too bright for my taste. they are very-very musical but analytic as well. a perfect combination of the HD800 and the LCD-2.
 
price
in Europe you have to pay about 5000 Euros for these, in the US less, and in Japan about 2500 Euros. That is a huge difference. They are an amazing deal for 2500 euros (that is approximately the price for the HifiMan HE-1000).

These arrived in the mail last week. I'm playing them with the Blue Hawaii SE amp. This review will not be too long as I like to be terse, and it is just not necessary to be wordy. These "earspeakers" are beautifully constructed and solid. They are light and comfortable on the head.
The imaging is natural and spacious. The sound is the most perfect of any transducer I've ever heard, and I've heard Wilson Audio, Focal Utopias, and numerous electrostatics in systems costing nearly a million dollars. The Stax SR-009's are simply better and sound more live and transparent, at least to me. They are very, very fast, detailed...even micro-detailed. But they do this in a very smooth and natural way which is not prone to causing listening fatigue. The finest treble and midrange available. Very good bass. Very good dynamics. But I must say, the Audeze LCD-3 fazor headphones, which I also own, are just a little bit better in terms of dynamics and bass for a lot less. But the Audeze is not nearly as good as the Stax in terms of transparency and natural sound.
The Stax SR-009's are thus very smooth, neutral, articulate beyond belief, dynamic, and an open clear window for any well done recording.

Originally published on November 11, 2012
 
Note: this review is an exact cross-post from post #1 of this thread on Head-Fi, which contains some user discussion on the review that may be relevant to read: http://www.head-fi.org/t/635893/mini-review-stax-sr-009

- download a printable 6-page PDF version of this mini-review (target goes to a location on my Dropbox)

Intro

I've been an owner of the HeadAmp BHSE for just over 3 years so far, which I use with the Stax SR-007 (OII MKI). My opinion of the OII/BHSE is that it forms the best headphone system that I've heard and is so amazing that it's changed me on the inside forever and continues to do so every time I listen to it.

Things just never stay still in the headphone world though, and when the SR-009 came out, of course I had to hear it. I got that opportunity at a few audio shows & Head-Fi meets over the last year, but those experiences didn't compel me enough to buy an SR-009 for myself. Despite that, I still remained optimistic and held out hope to one day hear one on my own system, to see if my CD player would make a difference. I finally got that chance recently thanks largely to CanJam@RMAF 2012, where I managed to acquire a loan from one of the most reliable sources that I know of (who shall remain nameless).

This mini-review is based on approximately 3 weeks of listening—not an ideal length of time for me, as I usually prefer to devote at least a month for a review, if not longer. My usual disclaimer applies: my opinion of the SR-009 shouldn't be considered final and is subject to change.

Reviewer Biases & Info, Equipment Setup, etc

For those who haven't seen it before, here's a link to one of my more recent mini-reviews; nothing has changed since then with the exception of my equipment setup: http://www.head-fi.org/products/audeze-lcd3-planar-magnetic-headphone/reviews/10298

Here's a breakdown of my current equipment setup:
- Source component: Plinius CD-101 (CD player) (power cord: Signal Cable Silver Resolution Reference - directly into wall)
- Analog interconnects: Emotiva X-Series XLR
- Headphone amplifier: HeadAmp Blue Hawaii SE w/ stock Mullard EL34 tubes (power cord: Parasound AWG12)
- Comparison headphones: Stax SR-007 (OII MKI)

Evaluation Music

CDs by the following artists/bands, by genre:

- Bluegrass: Alison Krauss & Union Station, Sierra Hull
- Classical: Carlos Kleiber & VPO, Julia Fischer, Nicola Benedetti
- Electronica/Trip-Hop: Goldfrapp, Massive Attack, Orbital, The Crystal Method, Trifonic
- Jazz: Dave Brubeck, Lee Morgan, Tord Gustavsen
- Rock: Porcupine Tree, Radiohead
- Metal: In Flames, Helloween, Megadeth, Meshuggah

Preconceptions & Initial Impressions

I had one big preconception of the SR-009 going into this review—I thought it would be like an electrostatic equivalent of the Sony Qualia 010. Not for any particular, logical reason, just an assumption based on informal listening in show/meet environments.

After having formally heard the SR-009 now, I'd now call my assumption to be false and I no longer think the SR-009 and Qualia 010 to be each other's equivalents in an electrostatic/dynamic kind of way. More to the point, I think the two headphones are clearly different from each other sonically. The Qualia 010 is probably best described as a very treble-oriented headphone, with a very wide & open soundstage, extremely clear-sounding, and fast (as in impulse response). To me, it remains the single clearest-sounding headphone that I've ever heard, of any type, eclipsing the SR-009 as well. Its treble also remains the best that I've heard to date—perfectly pristine and sharp. Not that the SR-009 had "bad" treble—it's just that I think the Qualia has the right amount of treble energy to make music sound realistically trebly, when necessary. I'm sure there are lots of people who would find the Qualia over-bright—but IMO, its treble quantity is perfectly realistic and remains my benchmark for all future headphones.

As far as initial impressions, to say that the SR-009 was a disappointment would be an understatement. I thought there'd be a significant difference between it and the OII MKI, but on first listen, I found that the two headphones were more similar than different and that the SR-009 didn't offer any immediately-obvious advantages over the OII MKI. It was clear that I'd have to do very critical listening in order to identify any sonic advantages it had.

Listening Test #1 - Synopsis

Although the OII MKI is admittedly my classical & jazz headphone primarily, I use it relatively often for other music genres as well, including electronica/trip-hop, folk/bluegrass, pop/rock, & metal. I consider the OII MKI as the single most "neutral"-sounding headphone that I've ever heard, of any type—almost every other headphone I've heard has had some type of overt sonic coloration, from brands like AKG, Audio-Technica, Beyerdynamic, Grado, Sennheiser, etc. The only other specific headphone models I'd class as close to "neutral" are the Grado HP1000 and JH Audio JH13 (IEMs). And no, I don't consider the Audeze headphones to be neutral either, though the LCD-2 r2 is certainly closer than the LCD-3. How do I define "neutral"? Mostly by the OII MKI and previously the HP1000—a balance between the bass, mid-range, & treble where none of them over-balance each other, providing a tone & timbre that sounds "realistic" when playing instruments that exist in real life, like a violin, which I'm intimately familiar with as a violinist. The OII MKI and the HP1000 are the only headphones, electrostatic or dynamic, that I've heard which I'd call neutral—none of the other full-size headphones I've heard to date deserve such a label, IMO.

With that said, I found that the SR-009 was relatively neutral-sounding too, though not quite as much as the OII MKI, with a marginal bass & mid-range detraction and slightly elevated treble. I'd summarize it as a somewhat brighter- and thinner-sounding OII MKI overall, but not excessively so, just marginally. And although I'd call the SR-009 "brighter" than the OII MKI comparatively, I wouldn't call the SR-009 "bright" per se, certainly not on the level of headphones like the Sennheiser HD800, let alone the Sony Qualia 010. The SR-009 was actually very well-balanced to me, easily more balanced-sounding than the dynamic (or orthodynamic) flagships that I've heard from Audeze, Beyerdynamic, and Sennheiser.

To summarize the SR-009's distinction versus the popular dynamics that I've heard: compared to both the Audeze LCD-2 and LCD-3, I'd say that it has a lot more clarity & treble quantity and a wider, more open soundstage. It's also more laid-back and passive-sounding compared to the assertive sound that the Audeze headphones have, without the visceral & tactile mid-range/bass either. I'd consider the SR-009 more loosely similar to the Sennheiser HD800, in that it has a similar level of clarity throughout the spectrum (but being better than the HD800), along with a similar passive sound, and a very generally similar sort of frequency-spectrum balance, except being better. Or to put it another way, I might say the SR-009 is sort of like a fixed version of the HD800 for me—less treble snarl/gnash, more mid-range quantity, more extended bass & treble, and a more accurate, smaller soundstage. (I'll note here that my HD800 thoughts are from it amped by the HeadAmp GS-X, and not a tube amp, which I might say is optimal for it.)

Listening Test #2 - Classical Music

My most critical listen throughout this review was classical music—specifically, the Adagio from the Violin Concerto in E major (BWV 1042) on Julia Fischer's Bach Concertos (or track 8 on this CD), which IMO remains the single best, most amazing display of prowess of the OII MKI/BHSE. There are so many awesome qualities that are revealed by the OII MKI, so my first question was, would this track sound even better on the SR-009?

No, it didn't, and the SR-009 actually ended up being somewhat of a bitter disappointment. Ok sure, the music still sounded technically "amazing" on the SR-009. It was also still way, way better than all of the dynamic headphones I've heard. And to its credit, it was still on the same plane of existence as the OII MKI.

However, the problem with the SR-009 was that it just wasn't as good as the OII MKI, and it had none of the OII's "magic" or x-factor either. On this track, the OII reveals so many details: Fischer's beautiful, pure, & radiating tone; a direct intimacy to her violin, so close you can practically hear into it; the vanishingly subtle rises & falls in intensity; an almost heat-like warmth quality; the organic sense of the orchestra. All of those details were subtracted with the SR-009—most of them completely! The SR-009's portrayal took away so many of those details that the music reverted to simply sounding like a really good pre-recorded performance and not something that was being played live, like the OII MKI can do.

I tried other classical CDs as well to round out the test and would put my position of the SR-009 for classical music this way: saying that the SR-009 is ideal for classical music would be like saying the same for the Sennheiser HD800—which is not something that I can personally agree with. I think of the HD800 to be a less-than-stellar headphone for classical due to some serious flaws, most notably the unrealistic & unnatural tone and timbre of the instruments in the orchestra, especially violins. It was the same way with the SR-009, which gave too much treble emphasis on violins so that they became wispy-sounding. Also like the HD800, the SR-009 "split" the 1st Violin section too much so that the violins sounded more like individual violins rather than a unified section body. There are only 2 headphones I've heard that properly portray the unified body concept, the OII MKI and the Grado HP1000—which should be the goal for accuracy, but most headphones fail to achieve it and the SR-009 was no exception.

Listening Test #3 - Versus The OII MKI

Comparing the SR-009 and OII MKI directly against each other across multiple genres of music was both educational and introspective—it repeatedly made me ask myself which headphone sounded more accurate, which one was more rewarding & satisfying to listen to, and most importantly, which was better, if one could be called better than the other.

I ended up concluding that the OII MKI essentially beat the pants off the SR-009. The SR-009 was certainly a very strong contender though, and I'd affirm that it's definitely among the best-sounding headphones overall of any type. Easily among the Top 5 that I've heard to date. I might as well list my Top 5 for reference (not necessarily in order, as I don't "rank" headphones per se): (1) Stax OII MKI, (2) Sony Qualia 010, (3) Grado HP1000, (4) JH Audio JH13, and now (5) Stax SR-009. Moreover, I'd call the SR-009 probably one of the most technically-amazing headphones that I've heard to date, after the Qualia 010. Very clean- & clear-sounding, inherently fast (i.e., impulse response), and appropriately diffuse-sounding with very good separation between layers/instruments.

But the SR-009 wasn't really that awesome next to the OII MKI. The most notable difference to me was the lack of "magic" or x-factor like the OII has. The OII was also simply more natural- & authentic-sounding in the mid-range with a fuller sound and heavier, more physical-feeling bass. Or to put it another way, the OII had more impactful drums & bass lines, heavier guitars, and more vocal presence. This made the OII MKI seem like a more musically versatile headphone, as it played electric & synthesized music very well too. I thought the SR-009 was at its best with primarily acoustic, laid-back types of music—classical, jazz, folk, etc. However, it didn't fare as well with trip-hop, pop/rock, & metal, as it lacked the OII's mid-range, mid-bass, & bass spark to really make them come alive.

I also felt that the SR-009's imaging was a step down from the OII MKI's. Granted, it did have a wide, deep soundstage that felt more 3D due to the increased z-axis depth and some added height as well, but it also felt narrower than the OII. More importantly, the SR-009 did not have clearly-delineated walls in the soundstage and felt very flat & vapid. Or in other words, it had a very limited ability to clearly render reverberation and the sense of sound waves reflecting throughout the virtual soundstage. It was because of this aspect that despite having a smaller soundstage, the OII actually sounded "bigger" and more "expansive" than the SR-009, as it allowed sound to really fill up "everywhere" to the point of hitting the walls, so to speak.

Needless to say, this affected "scale" as well, as the SR-009 never quite sounded as "big" as the OII MKI and consistently failed to deliver a sweeping "wall of sound" that wrapped from one end of the soundstage to the other. The SR-009's idea of a "wall of sound" felt like a small, translucent wall instead that was just sad in comparison.

Tube Rolling & Gain/Volume

I briefly tried the Genalex Gold Lion KT77s on the SR-009 and would have to say that these tubes had a better effect on the SR-009 than the OII MKI. I've found that these tubes add bass impact and more body to the mid-range, which was a better result on the SR-009 than the OII MKI. The KT77s didn't rectify the SR-009's sonic issues for me though, but there was still an appreciable added difference with them.

The issue of gain is one that's been reported by other SR-009/BHSE owners, but I didn't run into this issue myself, as my specific BHSE has a lower gain than normal due to its configuration of Stax Pro + Normal jacks. This made my BHSE well-suited for driving the SR-009, as I could achieve just about any volume that I wanted, even from the 4V RMS balanced output of my source.

On the subject of sensitivity, I found that the SR-009 required about 3 less steps on my DACT-configured BHSE to achieve approximately the same volume as the OII MKI. I also tried turning up the volume to moderately high levels on the SR-009 to see how it would respond and it continued to sound very good even at high levels. No issues or detractions that I can report from high volume.

Conclusion

The SR-009 ended up being about as underwhelming & disappointing to me as it is expensive, and I'd have to dissent with the prevalent opinion among other Head-Fiers that it's one of the best headphones currently in production, electrostatic or not. I saw it as essentially a step backwards from the OII MKI—enough that I'd degrade its ranking to "above average" from the OII MKI's "excellent".

I view the OII MKI as the superior headphone and recommend it instead for anyone truly seeking a serious & honest high-end electrostatic setup.

For reference, these are some other headphones that I rank as "above average"—Audeze LCD-3, Beyerdynamic T1, Grado HP1000, Sennheiser HD800, Shure SRH1840, and Stax SR-507. However, just because I classify the SR-009 as being "above average" doesn't mean I think it actually deserves the company of those other headphones, as I think it's better than all of them. It's just that it ultimately fell short of being "excellent" to me, as did those other headphones. As might be inferred, there's a lot of subjective gray area within my rankings, which is intentional—I've historically avoided numerically ranking gear for numerous reasons, not the least of which is that it's extremely subjective and prone to misinterpretation. The only reason I have a ranking scale that goes from "atrocious" to "excellent" is to help identify equipment that truly stands out from the rest. "Average" for me includes headphones like the AKG K2xx/K70x, most of the Audio-Technica woodies, most of the Grado models made under John Grado, Sennheiser HD6xx, etc—i.e., most of the venerable classics that sound very good to the highest cross-section of Head-Fiers with mid-level gear & experience. It's easy for most headphones to fall under "average" to me for this reason—there aren't very many that are below-average or atrocious to me. "Below-average" to me includes the Audio-Technica ATH-ES7 and Sennheiser HD419 (both of which I own—yes, I'm critical even of the headphones that I own!) and the new Denon AH-D7100, for example. Finally, "atrocious" includes Apple iBuds. Enough said?

My ranking system is in place primarily for two reasons: (1) to help set reasonable expectations for newbie or mid-level Head-Fiers seeking to upgrade, (2) to help equalize the field among the high-end options for high-level Head-Fiers seeking to sidegrade or upgrade—i.e., someone who's heard as much dynamic gear as I have who thinks the HD800 is one of the best headphones available might come to the conclusion that he might not need to get an SR-009 or the BHSE. Or someone who already owns the SR-009 and BHSE might conclude that he needs to try an SR-007. Or conversely, someone who owns the OII MKI and BHSE might conclude that he doesn't need to try the SR-009.

Related Reading

- Stax SR-007 & HeadAmp Blue Hawaii SE review & story: http://www.head-fi.org/t/598589/review-story-stax-sr-007-headamp-blue-hawaii-se
- Audeze LCD-3 mini-review: http://www.head-fi.org/products/audeze-lcd3-planar-magnetic-headphone/reviews/10298
- Beyerdynamic T1 review: http://www.head-fi.org/products/beyerdynamic-tesla-t1/reviews/10295
- Sennheiser HD800 review: http://www.head-fi.org/products/sennheiser-hd-800-headphones/reviews/10294

Addendum - Review Notes

My review notes are included here in their own section for convenience. These provide specific detailed info not included in the review. Notes start below the asterisks.

***
009 not the electrostatic equivalent of Qualia, as previously thought.

009 imaging more divergent/diffuse. More front- & center-loaded, not as close & wide as 007. Almost like a shell, but large. Instrument positioning further away, yet lacks the "air" of the 007 that allows details like reflected sound to be heard on it. Reflected sound not very apparent on 009. Room acoustics in general not as clear on 009 as on 007.
 
Spatially-larger imaging on 009—narrower width than 007, but more depth & height, more of a 3D-like effect. More "air" in the acoustics. Somewhat HD800-like, but not as much as HD800.

Deeper mids & bass on 007—more of a heavier, almost physical sound, for a stat that is (dynamics tend to sound more physical than stats). 009 lighter- or thinner-sounding with more treble quantity, but not as much as Qualia (or even the HD800). Relative to 007, not absolute.

SR-007 consistently more percussive sounding (harder-sounding pops).

Despite lack of stats sounding "direct" in general, 007 sounds more direct & assertive than 009. 009 more laid-back and passive.

Reverb more pronounced on 007, allows ambient electronica to sound more "space-filling" than on 009 where it sounds vapid. Sounds "bigger" on 007 due to clearly-delineated walls. No clear "walls" on 009. 009 like HD800 in this aspect—neither has walls, they just sound open & empty yet flat at the same time.

Violin tone more natural/authentic on 007, more wispy & ghostly on 009. 009 also reduces "unified body" of 1st violin section—too much of an individual-violins effect, not enough of the group effect. 007 renders a properly intact 1st violin section. 007 also tends to put the listener position at the conductor; 009 puts the listener in the audience row. 007 also renders more detail in violin-bowing technique—speed, inflection, etc.

009 loses the 007's magic/x-factor—the intensity, the live-performance surrealistic immersion. 009 slides back to more of a pre-recorded music feel. 007 has a more tactile/visceral sound, esp in bass/mids. 007 has more depth/richness/fullness in mids than 009—i.e., violins & vocals "swell" more on 007. 007 has more "fill" factor. 007 capable of a more powerful/intense sound.

007's smaller soundstage and mids better-suited for jazz. 007 "brassier" and "reedier" sounding than 009, which loses those elements.

Piano semi-plinky on 009—lack of depth/weight to notes. Not enough "weight" to various instruments on jazz recordings on 009, notably piano & brass (Dave Brubeck, Steve Kuhn). A440 that should "pound" on Brubeck's Time Out LE doesn't really pound on 009. More integrated imaging on 007 better for jazz, puts listener more in with the group (a la Grado HP1000, but not as much).

Julia Fischer Bach Concertos track #8: 007 captures a more beautiful, radiating, pure tone on Fischer's violin than 009. The almost heat-shimmering radiance not there on 009. 007 also has more of a chamber-orchestra feel than 009 in terms of the imaging, like you're in with the orchestra, practically right next to Fischer, which is probably more accurate. 009 has more of a sitting-away-from-the-orchestra feel. 007 does have smoother treble, sort of negatively affects edginess of harpsichord specifically, but nothing that overly detracts from it.

CD albums used for review:
- Alison Krauss & Union Station - So Long So Wrong, Paper Airplane
- Carlos Kleiber & VPO - Beethoven Symphonies 5 & 7
- Dave Brubeck - Time Out [Legacy Edition]
- Goldfrapp - Black Cherry
- Helloween - 7 Sinners
- In Flames - The Jester Race
- Julia Fischer - Bach Concertos
- Lee Morgan - Tom Cat [AudioWave/Blue Note XRCD]
- Massive Attack - Blue Lines, Mezzanine
- Megadeth - Countdown To Extinction [Mobile Fidelity Sound Lab]
- Meshuggah - Chaosphere
- Nicola Benedetti - Fantasie
- Orbital - Snivilisation, The Middle of Nowhere
- Porcupine Tree - In Absentia
- Radiohead - OK Computer
- Sierra Hull - Secrets, Daybreak
- The Crystal Method - Vegas [2007 Deluxe Edition]
- Tord Gustavsen - Changing Places
- Trifonic - Emergence

As the subjective sound quality of the SR-009 has been extensively discussed in the other reviews, I will focus on my objective experiences. Whenever I purchase new high-end products, I always choose to run a blind test consisting of the model in question alongside other high-end headphones. This time, the comparison counterparts included the LCD-3, HD800, HD650 and Orpheus. 
 
My subjective impressions always tend to take a similar route: there exists a very strong correlation between the price tag and the sound quality that I perceive. It was no different this time. Therefore, I performed the blind test on ten participants who are all fellow classical musicians in a blindfolded setting (with the volume matched etc).
 
The results this time were indeterminate. However, the HD800 came last followed by the Orpheus. After the blindfolds were removed, the Orpheus was unanimously agreed as having the best sound quality (the Orpheus does look rather magnificent). The Stax was chosen to have the best sound quality by three people.
 
This kind of test demonstrates that all these high end headphones do not have such a huge disparity in sound quality as made out by other subjective reviews. Therefore, I am always slightly let down by products with such a steep price tag as the Stax. Evidently it is not as steep as the Orpheus, however, for this money, I believe it is more worthwhile buying a pair of speakers.
 
I believe it is also important to stress that the superlatives associated with this headphone should be taken with a grain of salt, in fact several pounds would suffice. I do not think that the SR-009 sounds bad. On the contrary, I believe it sounds fantastic (I had very similar experiences to Currawong's review). However, as this test has demonstrated, it does not outperform other high end counterparts with noticeable significance (this is especially noteworthy as the other test headphones except for the Orpheus are considerably cheaper than the Stax). 
 
Hence all in all, I believe that the SR-009 is an outstanding piece of gear, but by no means the King of headphones.

Since I have had them for a while, I can say that they are a real pleasure, every day, every week, every month. I just don't get tired of them. I can use words like balanced, neutral, spacious, detailed, but those really don't distinguish them enough. They are all of that, but they are totally non-fatiguing. I can listen to them for hours on end, and still want to hear more.

I am driving them with the Blue Hawaii Special Edition, which only adds to the delicious experience of these headphones. When I listen to well recorded and mastered DSD files, it almost takes my breath away. That eerie feeling that the instruments and voice are right in the room with me is uncanny.

I am a very happy head-fier. I don't even mind that I paid a premium for these headphones as an early adopter.

 
Compared to most of the competition, this is inarguably a wonderful headphone and I do enjoy it. But sonically, it does not compete with a well-driven O2 mk1 to my ears. I simply find the O2's richer and more involving tone to be more natural.  

The 009 is more alike the Lambda series than the Omega series. It's no harder to power than the Lambdas and the sound signature is reminiscent, but probably a step up in refinement, soundstaging and bass extension/impact. In general though, the sound is typical STAX. Natural, agile and very detailed. But then again, compared to the O2 mk1 it falls short. Particularly in the midrange, which lacks the organic presence of the Omegas. 

The build quality is excellent though and certainly on par with what you can expect for your $. Precision-engineering all the way through; looks fantastic and feels substantial. Super comfy to wear as well. I have no issue with regards to the fit & finish of this headphone - it looks and feels like an expensive, high-end product. 
 
But with a price that's pretty much DOUBLE that of the O2s at this time, I do not consider this headphone to be a very solid investment. The O2 is more demanding in terms of amplification, which can get expensive, but when driven to it's full potential the O2 mk1 just sounds better to my ears. 

Just my 2 cents. 
 

Knowing where to begin describing these is hard. The closest I can come is my first experience listening to a pair of full-size swiss Piega loudspeakers back in the early '90s. The resolution of those things was so incredible I thought that they reproduced the notes of a double-bass with such amazing resoultion you could hear the detail of the strings vibrating and that's before you get an idea of what their ribbon tweeter could do! Similarly, I recently experienced the capabilities of the Linn Klimax Twin power amp on a variety of speakers. The absolute authority and perfection of its presentation was something to behold and it immediately drove me to wonder how it might be possible to afford one.

Similarly the 009s have had such an effect on friends who have listened to them. Much like the Omega IIs and a suitable high-end rig, it is possible to make out the form of the studio music was recorded in by the detail of the echo off the walls. Listening to a classical concert I can even hear the detail of the waves of echos from the instruments coming off the walls. With these earspeakers, as Stax terms them, it is as if everything is simply on another level compared to dynamic headphones. Only the more recent high-end orthos, such as the LCD-3s and Hifiman series and maybe the HD-800s, Sony R10s and my Symphones Magnums come anywhere close. Now the SR-009 takes all this to yet another level. In the same way the first time I tried Stax and compared them to my regular headphones everything was so much more clear and real, the 009s have achieved this over even the orthos, which I hold in the highest regard. Questions about resolution, harshness, distortion, ringing and other issues simply seem not to exist.

While Stax will never give quite as much impact, or slam to music as othos can (while maintaining a high level of detail), the orthos, already awesome in this regard, especially with something like a high-end hybrid amp, wont give you instruments and voices with as much clarity as 009s, if they are arguably better all-rounders. The limits are only set by your source and amp, especially the former. I could easily visualise a $25k system with a pair of these (along with a Liquid Lightening or Blue Hawaii SE and Esoteric K-01 DAC).

Tonality-wise they are similar to the old-style Omega I and Lambda, that is, quite a bit brighter than the Omega II, which was always the odd one out in terms of sound. They suffer, like other models, from the "Stax fart" where moving your jaw and breaking the seal causes the protective membranes to make a sucking sound. However, like the original Omega and unlike the Omega II, they seem to be less difficult to drive, with detailed bass even from the older amps, such as the T1S. A good combination I found was the NOS Metrum Octave DAC, which is relatively mellow but still detailed, along with the Stax 727A amp. This gave a number of people an OMG moment listening to acoustic music, though it was not quite the ticket for rock. The bass, like the power output of a Rolls Royce, is "sufficient". The LCD-3 I found more entertaining in that regard.

They are again similar to the Omega I in that they come in an elegant wooden box with the nicest foam of any box I've encountered in recent memory. Opening it up, I was greeted with a "new car" smell, suggesting they source the leather from a factory that makes car seats. The headband has a new 10-click (per side) adjustor, which is quite stiff to adjust but holds firm unlike the old Lambda headbands. Beyond that, the fit is typical Stax -- light and comfortable. The aluminium design is of the highest quality, if it does seem to contrast the rather simple headband arrangement. Like its maker, it is in many ways an understated design, its statement in its perfection of design and sound.

So, ultimately, we have our king. Long live it and its maker I reckon.

(Updated June 23, 2012)