My Electrostatic Headphone Adventures

tmallin

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Background

My recent electrostatic headphone purchases are not my first foray into electrostatic headphones, not by a long shot. I was an early adopter of the Koss ESP/6 electrostatic headphones many decades ago, back in 1968. Yes, they were heavy and uncomfortable, with considerable clamping force. And they had their problems due to their "self-energizing" feature which used the audio signal to polarize the electrostatic elements. This caused the sensitivity of the phones to vary considerably with classical music which had long periods of quiet playing. This was something the factory seemed unable to correct despite my sending them back a few times. But when they were "on," they undoubtedly sounded better in important ways, such as clarity and audible detail without added brightness, than any other headphones I'd ever experienced.

The 1971 ESP/9 was better-yet sounding and did not suffer from the varying sensitivity problem. Removing the self-energizing feature from the headphones themselves to a black box helped the weight and reduced or eliminated the varying sensitivity problem. They were still heavy, however, and the clamping force was just as considerable.

When the various Stax electrostatic earspeakers became available a few decades ago, I listened periodically at audio dealers. The Stax were and are very light by comparison, had low clamping pressure, much larger earcups, and were, of course, open-backed, unlike the early Koss products. Yes, they were yet clearer sounding than those Koss models, but at least part of this was due to the fact that they always seemed bass light and treble strident to me, not at all the basically honest warm tonality of the Koss products.

Koss ESP950 Headphones

The current Koss ESP950 headphones have been in production since 1990, almost 30 years now. By the time they were introduced, I was not listening much to headphones and never really auditioned them. My early headphone adventures are discussed a bit more at the beginning of this earlier thread here in Tom's Corner.

As I now know, my failure to hear the ESP950s for all those years was my loss. After I regained interest in headphone listening a few months back, I concentrated on much more recently introduced dynamic and planar magnetic offerings as documented in the above link and here and here. About the time I purchased a pair of Janszen Valentina Active hybrid electrostatic speakers I also ordered a pair of Janszen's hybrid electrostatic headphones, but despite VERY promising working prototypes being demonstrated at the last couple of AXPONAs, these have yet to see the light of day as a commercial product.

I've listened at AXPONA to some of the newer electrostatic offerings, primarily from HiFi Man and Mr. Speakers. While the HiFi Man versions do sound clear enough to distinguish them from the company's non-electrostatic headphones, they are impact light and treble heavy. The Mr. Speakers Voce are indeed the best in that company's line, but to my ears have not sounded so stunning as to warrant the investment for phones and the separate amp needed to drive them.

Second System

When I first moved to my new home in 2015, I had two dedicated rooms. The realities of married life and new interests cut that back to one converted bedroom for the last couple of years. That's fine, and I'd been able to combine my speaker and headphone listening in that one room with the help of extraordinarily fine headphone amps, most recently the Benchmark HPA4.

But last Christmas I treated myself to a new Dell XPS 7760 27" Touch 4K Ultra desktop all-in-one computer for my home office. The configuration I purchased is described here. The new computer has both extraordinary video quality as well as the best audio of any all-in-one. I thus found myself spending an increasing amount of time watching movies and other video programs at my office desk on the "big" screen—big because at my usual desktop viewing distance that 27" screen has a subtended angle similar to the biggest screen cinema from the front part of the theater.

Yes, the audio speakers that come with that Dell are quite fine—for computer audio. They are not like a high-end audio system, however. But plug in my $200 NAD Viso HP-50 headphones into the stereo mini jack and we are really talking some very fine sound as long as all the special processing available from the soundcard is bypassed. For awhile, I was content. As I've mentioned repeatedly in my prior headphone ramblings, I have great admiration for the sound quality of those NAD phones and their high sensitivity and warm balance make them a perfect match for the relatively low power available from a desktop computer's audio amp.

Then I saw an eBay auction for a brand new Koss ESP950 electrostatic headphone system. I figured the winning bid wouldn't be much higher than the current $500 price for the MassDrop version ESP95X, quite a discount from the usual $1,000 retail of the Koss version, not to mention the $2,000 retail price when the ESP950 debuted almost 30 years ago. My survey of some online reviews indicated that the ESP950 has garnered quite a bit of respect from both owners and professional reviewers over the years with most finding the quality of voice reproduction, the midrange in general, and the overall tonal balance to be strong points of its natural-sounding reproduction. I took a "small" (in terms of my overall headphone investment at this point) gamble and made a bid that I believed could not fail. I did in fact end up winning the auction for just over $600.

First Listen

From first listen the Koss ESP950 everything I hoped it might be, and then some. I knew from the first few moments of listening that these were very special headphones indeed! The overall tonal balance was stunning, as was the level of audible detail and clarity without added brightness. The phones are extremely light in weight, lighter even than the Mr. Speakers Ether 2 which I recently raved about. Not only that, but head clamping is almost non-existent, making the Ether 2s feel, by comparison, like having a vise on my head.

I cannot stress enough the basic difference in sonic quality between these electrostatic headphones and the best of the dynamics and planar magnetics I have for comparison. There is so much more audible detail and nuance, both tonally and dynamically, from lowest bass to highest treble. Okay, I still feel that the lowly NAD Viso HP-50 is the closest to perfection in terms of overall tonal balance. But the NAD bass sounds a bit thick and heavy by comparison, whereas the Koss sounded a bit too thin in the bass for overall neutrality, but for the first time I could hear where the NAD might be erring a bit in terms of balance.

But aside from the overall balance issue, the Koss ESP950 is just so much clearer and obviously lower in distortion than the NAD or any other dynamic or planar magnetic phone I've experienced. And even in the bit-thinner-than-natural bass, there is enough to make me doubt the thinness at many junctures—and there is just so much detail without any over-brightness. Okay, like electrostatic speakers, there is a lack of bass punch and drive compared to dynamic and planar magnetic drivers, but even in the bass the increased clarity and nuance makes up for that on most material.

Keep in mind that for these initial impressions I was comparing the sound of the NAD Viso HP-50s with its stock headphone cable fed from the audio-out mini-stereo jack of my Dell computer compared to the ESP950 fed from the same audio out mini-stereo jack of my Dell computer via the stock stereo miniplug to dual RCA plug cord which came with the Koss phones, to the stock Koss E90 amp/energizer, with the ESP950 played from the Koss E90.

[Continued below]
 
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tmallin

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[Continued from above]


Issues?

As you can imagine, for a product which has existed in basically an unaltered state for almost 30 years, there are any number of online extended reviews, comments, and discussion. I refer readers, for example, to the 229-and-counting-page thread on the ESP905 headphones on the Head Fi website. These have revealed a few issues which have concerned long- and short-term users.

Look and Feel

Many say they think the ESP950 headphones and E90 amp/equalizer look and feel cheap, very plasticky, and thus rather overtly not high quality, or at least not something you can be proud to display to your audiophile buddies. Well, yes, much of the visible material used IS plastic. The phones could not possibly be as lightweight as they are without most of the structure being plastic rather than metal, wood, or leather. Even the E90 case is plastic, with the result that it weighs only a few ounces, lacking the heft a "real" amplifier ought to have. Frankly, when something sounds this good and feels so comfortable on my head, I can totally forgive the look and feel of the parts. Part of the reason for all the plastic parts is . . .

Portability

From the start, the ESP950 headphone system was touted as the first portable electrostatic headphone system. Now "portable" in 1990, you have to understand, meant something much different from what we mean today in the era of portable electronic devices of the iPhone/Android ilk. Think, instead, of the way SLR cameras and their associated lenses and paraphernalia were portable in terms of size and weight in largish, over-the-shoulder bags, compared to the larger format cameras of yore. The ESP950's leather carrying case (yes, the case IS real leather, as opposed to pleather) is similarly sized and has places to hold all the goodies you would need for a 1990s portable system, including CD jewel boxes. There is a battery pack which holds 6 C batteries, good for powering the E90 amp/energizer without wall power for about three hours. Such portability is not a concern for me. I don't plan on using the ESP950 on the go at all.

Noise

Many owners and some reviewers complain about an intermittent ripping/tearing/crackling/whooshing very-low-level noise audible from one or both earphones when music is not playing through the headset or during pauses in the music or when very quiet music is playing at very low volumes. There has been endless speculation about the cause and potential cures for this noise. Some say that the noise vanishes after the headphones are returned to the manufacturer for repair/replacement, and some says the noise recurs or was not affected at all by the repair or replacement. Some say the noise appears and disappears unexpectedly and sporadically over time. Some never experience any such noise even after many years of ownership.

I occasionally experienced such noise even with my early Koss ESP/6 and ESP/9 headphones. I also occasionally experienced such noise with hybrid electrostatic speakers I've owned, such as the Janszen Valentina Active and Sanders 10C.

I experienced this noise briefly with my new ESP950 headphones even on first listen. In my case, for the ESP950, the total—and so-far permanent cure—has been proper orientation of the two-prong, non-phased power plug of the wall-wart power transformer for the E90 amp/energizer. Once I found the correct orientation for that power plug (i.e., which prong should be attached to the hot side of the 120-volt AC wall outlet), the noise vanished.

Warranty

Almost everyone agrees that despite any quality problems with an ESP950, the Koss warranty stands head and shoulders above all the rest. It is basically a no-questions-asked offer to repair or replace any part of the ESP950 system for the life of the original purchaser. There are many testimonies as to the fast turnaround speed of warranty repair, in addition to the fact that in fact Koss doesn't require proof that you are the original purchaser. Thus, used units sell easily since any problems can be taken care of by the factory with no questions asked. About the only type of warranty claim which might not be honored involves intentional physical alteration of the unit, such as to correct . . .

RCA Jack Clearance

There are many complaints about the lack of clearance around the RCA jacks on the back panel of the E90 amp/energizer. As folks have noted, only the smallest diameter RCA plugs, like those found on the cheap-looking stock cords provided with the ESP950, will fit through the chassis holes so as to allow full insertion into the circuit-board-mounted RCA jacks.

The plastic back panel of the E90 can very easily be physically modified to allow use of even the largest-barrel RCA connectors. You unscrew four small screws in the back panel and it comes right off. Then you can use a file or other tool to enlarge the two holes for the left and right RCA jacks. Clean off any small plastic shavings, then reinstall the back plate. The whole operation took me maybe 15 minutes to complete. I filed away as much plastic as I could without making the R and L designations for the jacks unreadable.

Some say this modification will void the warranty. If so, I guess I'm stuck. But given the availability of replacement parts from the factory, I'll take my chances, especially since, as described below, I no longer need to use the E90 anyway.

Lack of Room for Modification Inside the E90

Aside from the warranty issue, others complain that the E90 case is so small and so tightly packed with components, that swapping out components for "better sounding" ones is physically difficult to impossible. Perhaps so, but the E90, for being included in the Koss or MassDrop price, seems to me to work just fine as is.

Difficulty in Channel Tracking When Adjusting Volume Control of E90

This is a genuine issue only for those who actually regularly use the volume control of the E90 to adjust the SPL one hears through the headphones. Unlike most other volume controls which double as a balance control by allowing separate volume adjustment for left and right channels on concentrically mounted controls, the E90 has no friction clutch on the concentric controls. This means that unless you carefully grasp both the inner and outer sections of the volume control each and every time you adjust the E90 volume control, you will certainly end up with the channel balance off center.

The work around is adjust the two volume controls so that they are balanced, and then carefully put tape or glue at the juncture of the two volume knobs so that they only rotate together and thus preserve system balance. I recommend using well recorded correlated pink noise to make this adjustment, such as the 2 Hours of Pink Noise recording online. In any event, on my E90 sample at least, the two volume knobs are mechanically mounted correctly so that the faint black-on-black line markings on the left and right segments of the concentric knobs do in fact line up with each other when the sound is subjectively balanced on such a test.

In my computer-based system, I find using the computer sound card's volume control to be much easier to use anyway since it only involves a key tap. In addition, proper gain structuring suggests that, in order to minimize distortion and maximize signal-to-noise ratio, as long as the computer's volume control is not set so low as to be truncating bit resolution, the last volume control in the system chain, that of the E90, should be set as low as reasonably possible.

Thus, for me, that means setting the E90 gain control at about 9:00 to 10:00 position and just leaving it there. This allows my computer soundcard to be set on 100/maximum for the quietest source I regularly use, which is BBC's Radio 3 internet station when playing Radio 3 source material at the highest volume I need. On most other material, I find the computer volume control operating between 28 and 70 at my favorite listening levels.

[Continued below]
 

tmallin

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[Continued from above]

Ear Pads

There has been much discussion of the quality—or lack thereof—of the stock ear pads of the ESP950. Many say they wear out quickly, do not make an adequate seal around their ears, and make their ears sweat after more than a few minutes of use.

As far as the wearing out, Koss still supplies replacement pads for $5 a set. That is not a misprint. Buy a few pairs at a time if you are worried about possible wear.

For my head and ears, the stock pads seal fine and do so with very minimal pressure against my head. They are exemplary in this respect.

Neither do I experience any ear sweating with extended listening of up to more than three hours at a sitting. Honestly, who listens longer than that without removing headphones? Even if you wear them all day while working from home, you certainly will remove them for several minutes or more for meals, snacks, and potty breaks.

But so many people online talk up the improved sound quality provided by aftermarket pads that curiosity got the best of me. The pads most talked about are the hand-made leather replacement pads for the Koss ESP-950 headphones from Vesper Audio marketed in the USA by Darin Fong Audio. Many folks online say these are not only more comfortable, eliminating any sweating problem, but also claim better sealing and higher sound quality. Everyone does admit, however, that swapping out the Koss pads is not easy, requiring the patience of Job to get the edges of the new pads into the slots around the ear cups.

Well, to me, for my ears, this turned out not worth doing. Yes, the pads are nice and soft and cushy and perhaps they make the ESP950s look a little more "professional." But I did not notice any increased comfort. The replacement pads are heavier than the OEM ones, making the headset heavier. The new pads, being thicker than the OEM pads, also increase the head clamping force, reducing comfort further still. Perhaps the seal may be better for some heads but, for me, both the original and replacement pads sealed very well.

I noticed no increase in bass extension. If anything, to me the bass extension was superior with the OEM pads, despite less head clamping force. The replacement pads did warm up the midbass and lower midrange a bit. Perhaps others like this change. To me, it was at best just a difference and actually I preferred the balance of the OEM pads in this region.

What really made the replacement pads a non-starter for me was that they messed up the very fine midrange balance and quality of the ESP950 with OEM pads. With the Vesper pads, the midrange of the phones loses more than a bit of that magic midrange naturalness. Also, contrary to the opinion of most who have tried the Vesper pads, I found the Vesper pads also made the staging more closed in and not as open and expansive as the original pads. I further found the high frequencies with the original pad to sound at least as nice as with the Vespers.

I did agree that the Vesper pads are a royal pain to install. You have the stretch them with quite a bit of force as you simultaneously have to force the soft leather edge of the pads into the slot. I eventually found that the flat edge of a credit card helped this process a lot since it allowed me to push an inch or more of the pad lip into the slot at a time. You also should start inserting the pad edge with the seam in the pad at the bottom, centered on where the cable enters/exits the earcup. Figure on at least a half an hour to get the first cushion on, less once you learn the technique.

Swapping the OEM and Vesper pads back and forth for repeated comparison is not something you should plan on doing. I did it twice, but never again. The OEM pads are themselves pretty difficult to put on once they are off, taking at least 15 minutes of work for the first one. For the OEM pads, the corner of a credit card works well to poke the stiffer lip of the OEM pads into the slot a fraction of an inch at a time.

My recommendation: save money and aggravation and stick with the OEM pads. Buy a couple pairs of replacements from Koss in case they wear out or get funky looking.

Non-Standard Amp Connection

Yes, the Koss phones have a unique connection. They require an electrostatic headphone amplifier or energizer, but have their five pins arranged in a rectangular pattern, rather than the circular pattern that is "standard" for Stax and most other electrostatic phones. Thus, while the Koss ESP950 will certainly work (very well indeed!) with other amps besides the OEM E90, you will need to re-terminate the end of the cable or use an adaptor. Re-terminating the wire is not for the faint of heart, from all accounts. I used two different adaptors, both with great success in driving the ESP950s from other electrostatic headphone amps. One is a long cord adaptor, again marketed by Darin Fong Audio here. The other, more ideal for a desktop set-up like mine, is a six-inch adaptor marketed by Mjolnir Audio here.

Lack of Replaceable Headphone Cable

This goes with the territory of electrostatic headphones generally. Most such headphones have non-detachable headphone cables. You are more or less stuck with the OEM cabling. Some believe this is for safety reasons, to avoid accidentally exposing users to the extremely high voltage used in electrostatic headphone connections.

I understand, however, that the forthcoming Janszen hybrid electrostatic headphones will have a removable cord. Each prototype I've heard at AXPONAs has had a removable cord terminated at the headphone end with a standard TRRS miniplug.

[Continued below]
 

tmallin

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[Continued from above]

Source Quality

Since the OEM E90 amp/energizer accepts only analog inputs, either via RCA or stereo mini-jack, this would seem to encourage the use of analog outputs from your audio system or computer. While this certainly works quite well, yet higher quality sound can be had by using a higher-quality DAC to feed the E90. Indeed, I've found that using one of my favorite USB cables (the Oyaide reviewed here) to feed the USB output of my computer to the USB input of my new Benchmark DAC3 B with the RCA output of the Benchmark feeding the RCA inputs of the E90 produces a substantial uptick in the already excellent sound quality of the Koss ESP950 headphones, compared with feeding the E90 directly from the computer's analog stereo mini-jack. This finding agrees with online comments of many others who have tried high-end DACs with the ESP950.

The use of the intervening audiophile DAC fleshed out the bass end of the Koss headphones considerably, as well as further improving clarity in the mids and highs and further enlarging the presentation. Apparent distortion and background noise dropped yet further. The presentation moved out of my head and forward a bit more—still not up to the quality of the NAD Viso HP-50 in this respect!—but still a quite noticeable improvement, one which plays to the strong suits of the ESP950 by not impairing any of them but further enhancing them.

Whether this improvement is worth the extra $1,700 to you for the Benchmark only you could judge. For me, I found it quite worthwhile since the total package of the headphones and DAC were around $2,300, in the ballpark with the Mr. Speakers Ether 2, and producing sound which, except for bass impact and extension, was at least equal if not superior to what I hear from the Ether 2 in my main system also fed by Benchmark electronics, the DAC3 HGC plus HPA4.

E90 Amp/Energizer Quality

There are many online complaints about the lack of audio quality of the OEM E90 amp/energizer which comes with the ESP950. Many claim that after hearing the ESP950 with a better amplifier, the E90 sounds almost broken, or that it only gives you about 50% of the performance of which the ESP950 is capable. Given the almost universal opinion that a "better" electrostatic headphone amplifier is necessary to take the full measure of the ESP950's greatness, it was only a matter of time before I, too, succumbed to the "what if?" lure of such praises.

If I was going to go for an after-market amp for the ESP950, I wanted one which most everyone agrees is among the best for driving both the ESP950 as well as other electrostatic headphones, such as the Stax, Mr. Speakers, and Hi-Fi Man entries. While most agree that the Blue Hawaii SE is one such amp, I did not want a tube amplifier for this computer-based headphone set up. First, my desk area is a bit limited and the Blue Hawaii, with its two non-stackable chasses, has a very large footprint. Second, I did not want to constantly be worrying about whether the tubes were wearing out and would soon need replacing. Third, I did not want a major heat generator sitting next to me on the desk.

Instead, based on many online reviews and comments, I decided to go with a solid-state Mjolnir Audio amplifier, the KGSSHV Carbon. I know that the co-designer, Birgir Gudjonsson, usually known online as Spritzer (the other designer is Kevin Gilmore), thinks very highly of the ESP950, and that others have found the pairing of Mjolnir amps with the ESP950 to be an excellent one. Spritzer is regarded as one of the world's foremost experts on all things dealing with electrostatic headphones. Here is Birgir's description of this amp from the Mjolnir website:

It’s finally here, the KGSSHV Carbon. This is the first electrostatic amp in the world to use SiC FET output devices which are as close to triodes as transistors can get. The original design concept for this amp was born to tame the rough top end of the SR-009 but it grew from there to become the best solid state amplifier we have designed. Right up there with the BHSE and the T2 as the best amps of their kind all the power you could ever need, a lot of detail, huge and expansive sound stage and the best bass I’ve heard from an electrostatic amp. Kevin and I are very proud of this one. The Carbon design requires heatsinks which are at least three times the size of the KGSSHV mini so it was a real challenge to make the amp this compact. It did require a new power supply design so I tweaked the KGSSHV mini design a bit to fit the Carbon better plus it has a vastly oversized transformer.

The amp is about 13" x 13" x 4" including heatsinks and the volume control. It fits on my desk just fine. While it runs warm to the touch, it certainly does not have any surfaces which could be really hot to the touch the way tube amps can be. There is no mechanical noise. The amp accepts the full un-padded pro-audio level of the Benchmark DAC3 B without any issues. I run the Mjolnir amp's volume control at a constant 10:00 and control volume with the computer's volume control.

How does it sound? Well, the ESP950 bass now has real punch and added extension and the midbass is warmed a bit, but without any deleterious effects on the presentation of the midrange and highs. The KGSSHV Carbon further clarifies, further lowers perceived distortion, filigrees and further smooths the highs, and opens the stage up even more. I'd say the further improvement of adding the amp is at least as large as adding the Benchmark DAC3 B to the front end. The return on your investment is probably not as great, however, since this added improvement costs $4,800.

Powered by this Mjolnir amp, there is really no area where the ESP950 is inferior in presentation to any of the planar magnetic headphones I have (Mr. Speakers Ether 2, Audeze LCD-4, Audeze LCD-4z). Okay, the overall bass range of those is stronger and warmer yet, but not so well defined; powered by the Mjolnir amp, the Koss bass end leaves nothing much to be desired. So powered the ESP950 is also superior to the NAD Viso HP-50 in all ways except overall tonal balance (the NAD is still superior there, I perceive) and that "room feel" of having the stage presented in front of your eyes instead of in and around your head where the NAD is still king.

Koss ESP950 Summary

Overall, unless you can and want to spend much more money on a pair of electrostatic headphones, the ESP950 is where you should be, I think. Right out of the box, in many ways, it is obviously audibly superior to the best dynamic and planar magnetic headphones I've owned or heard, and I think I've owned and heard. If you like to hear audible detail without added brightness, if sonic clarity and low subjective distortion push your buttons, then this is the best-buy ticket. Whether you operate the system straight from a computer, add a better DAC, or go all out and also add a better electrostatic headphone amplifier, the ESP950 scales very well and will not disappoint.

[Concluded below]
 
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tmallin

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[Continued from above]

Stax SR-009S

That's not to say that the Koss ESP950 is the best electrostatic headphone there is. The Stax SR-009S, my latest headphone purchase, is better still in most ways. But the cost is high, some $4,300 versus at most $1,000 for the Koss. I'm glad I purchased the Stax, but then I just had to have one of the very best headphones around.

What extras does $4,300 buy you in the case of the Stax SR-009S? Well, for one thing you get a solid very lightweight wooden case instead of a leather carrying case. You also get a pair of the most elegant looking headphones around. The shiny aluminum and leather materials are obviously much more costly, much more professional and serious looking than the plasticky Koss. You get real gold plating on the stator elements. The headband adjustment has 10 repeatable settings rather than the rather loose infinitely adjustable sliding adjustments of the Koss. The earcups pivot in all planes rather than just back and forth as in the Koss. Compared to the adaptors I was using with the Koss, the Stax plug connecting the phones to the amp is also sized very nicely with generous gripping area for pushing and pulling the plug into and out of the relatively tight fitting connector on the Mjolnir amp.

You also get a lot more weight on your head, however, with the Stax hefting a full pound rather than the 12.45 ounces of the Koss. And while the leather cushions of the Stax are very plush and comfy, there is definitely a lot more clamping pressure on your head with the Stax compared to the minimal clamping of the Koss. Also, because of the high arc of the headband, the increased weight of the Stax seems more than the four ounce difference would indicate. With the Stax, much of the weight is in the high-off-your-head arc of the headband—an unusually bulky and odd-looking-on-your-head design. Unless this arc is centered just right, it tends to torque your head and neck, making the weight of the headphones seem more onerous than the specs would indicate.

You also get a longer cord, 2.5 meters with the Stax. That would be very helpful to avoid the need for using a cable extension when listening in an ordinary audio system from your usual speaker-listening seat. For my desktop system, however, this longer cord, compared to the 47-inch cord of the Koss, is no help and just gets in the way if not rolled up. With the Stax at my desktop system, I leave half the cord rolled up and clamped with a wire tie.

The sound you hear from the Stax is also unusually sensitive to objects near the headset, such as your hands. Don't try the judge the sound with your hands holding or anywhere near the headset, in other words. The midrange naturalness is severely affected by the proximity of anything other than your head.

But those are nits. Once settled properly on my head and with my hands away from them, these things sound extraordinary indeed! The tonal balance is right up there in terms of naturalness with the NAD Viso HP-50. These, like the Koss, are a little lightweight at the bottom end, while the NADs are a little warm in the lower reaches. The NAD bass extends further down, but the Stax high end, unlike that of the NAD and less so the Koss, seems to extend forever upward and is more filligreed than any other headphone I've experienced, right up there with the top-octaves naturalness of my Harbeth M40.2 speakers.

And then there is the transparency/clarity and low distortion. In this respect, the Stax are literally breath taking! Everything is so sorted out and precisely presented. Little musical and venue details unheard with other speakers or headphones are clearly revealed and easily identifiable as to origin, moreso than with any other transducer I've experienced. Yet they don't sound too bright or treble heavy in any way. These are thus the most transparent transducer of any kind I've heard, speakers or headphones.

In isolation, they also don't sound at all thin in the lower reaches. It's only when compared to other, weightier-in-the-bass/lower-midrange headphones (e.g., Audeze and NAD) that you can recognize what is missing here. I'm sure the lack of lower-range weight artificially enhances the Stax clarity, but that enhanced clarity and the overall tonal balance after just a few minutes of listening sounds so right that I don't care.

The overall stage presentation is also the largest and most focused I've heard from headphones, as well as having considerable depth for headphones. No, the sound is not as "out there" in front of my eyes as it is with the NADs, but these are the closest approach to that aspect of the NAD performance I've heard with other headphones.

Another Stax model, the half-the-price Stax SR-007Mk2, probably offers a tonal balance closer to the NAD in terms of midbass/lower midrange heft than the flagship SR-009S. It also has a more polite, less projected midrange. Some, like Spritzer and Jude of Head-Fi, actually prefer the sonics of the SR-007Mk2 to those of the SR-009 models, at least when the SR-007Mk2 has its bass port modified by filling it with Blu-Tack and perhaps the springs in the cushions enlarged.

But all agree that the SR-009 is more detailed and yet clearer. For me, THE most important quality of electrostatic headphones, the quality I feel puts them at the peak of the headphone world in terms of performance, is the added detail and clarity without perceptible excess brightness. All also agree that the latest SR-009S model I have has tamed any excess brightness which some heard in the original 009. The KGSSHV Carbon amp I use was also specifically designed to fill in the bass end and tame the high end of the SR-009. Thus, I feel confident in having the best Stax system for my listening preferences.

But, who knows . . . I may get a pair of the SR-007Mk2 down the road, just to be sure.
 

tmallin

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Here are a couple of photos of my computer audio system. The headphone stands shown are the Acase leather (Stax) and Avantree aluminum (Koss, NAD). I highly recommend both. The Acase better fits larger, heavier headphones. I have two additional Acase stands for my Audeze phones and another Avantree for my Mr. Speakers Ether 2 in my main audio room. These are two of the very few headphone stands which come with a well or compartment to contain the headphone cable. The Avantree is better for headphones which you want to remove from the stand with just one hand. Removing headphones from the Acase requires two hands.




IMG_6702.jpg IMG_6701 95%.jpg
 
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tmallin

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The Stax SR-009S is even more perfect than I'd realized. Changes in my main stereo room audio system freed up a Triode Wire Labs/P.I. Audio Group Discrete USB Cable. Substituting the Discrete for the Oyaide USB I was previously using to connect my Dell Desktop's USB output to the USB input of my Benchmark DAC3 B produced a significant uptick in performance.

The space got larger and images are yet more focused. Everything is yet clearer and more relaxed sounding. Most of all, however, the highs lost any hint of remaining too-brightness and the lower registers filled out yet more. The tonal balance is now just about perfect--right up there with the NAD Viso HP-50 and oh-so-much clearer and more detailed. Jaw-droppingly impressive.
 
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