STAX SRM-700S Electrostatic Ear speaker Driver and SR-009 Electrostatic Ear speaker

In my first STAX article I take a look and listen to the awe inspiring SRM-700S driver paired with the SR-009 electrostatic ear speaker. Thank you to Audrey and Kay for making this possible.

STAX have not paid me to write this article.
I am writing this in the form of an article due to this being my first experience with electrostatic equipment and as such I have no means of comparison at this moment in time,
making a review difficult at this point.
Although The Audiophile Cafe is sponsored by STAX, the views and thoughts in this publication are my own unbiased opinion.
Audrey and Kay have been most gracious, kind and patient with me and I would like to personally thank them both.

The STAX SRM-700S currently retails at $3,400 at the time of this article.
The STAX SR-009 currently retails at $3,699 at the time of this article.

Follow these links for more.

Review equipment:
STAX SR-009.
STAX SRE-925S. ( Extension Cable. )
Burson Audio Conductor 3X Performance.
IsoAcoustic Indigo isolation feet.
KECES Audio ePhono and ePhono Power.
iPad Pro running Qobuz Studio Premier.
Technics SL1200 MKII.
Ortofon Quintet Red.
Isonoe Isolation Feet.
Pro-Ject Debut Carbon Evo.
Ortofon 2M Red.
QED, Custom Cans and Van Damme interconnects.
Audioquest NRG mains cables.
Audiowalle TP1000 mains conditioners.

Jean Michel Jarre – Les Chants Magnetiques. ( Magnetic Fields )
Jean Michel Jarre – Revolutions.
Jean Michel Jarre – Equinox. ( 180 gram )
Jean Michel Jarre – The Concerts In China.
Depeche Mode – Violator. ( 180 gram )
Pink Floyd – The Wall. ( 180 gram )
Tears For Fears – Songs From The Big Chair.
Gustav Mahler – Symphony No.5.
Mikaela Davis – Delivery. ( HI-RES / 48.0 kHz )
Lissie – Thank You To The Flowers. ( Redbook 16bit / 44.1kHz )
Chris Rea – ERA 1. ( HI-RES / 96.0 kHz )
Fleetwood Mac – Audiophile Collection. ( Redbook 16bit / 44.1kHz )
Mastodon – Once More Around The Sun. ( Redbook 16bit / 44.1kHz )
Kylesa – Static Tensions ( Redbook 16bit / 44.1kHz )
The Audiophile Cafe Demo playlist: ( mixed file formats )

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What’s in the box:
STAX SRM-700S Electrostatic ear speaker driver.
STAX Mains cable.
Wood engraved presentation box with foam cushioning.
STAX SR-009 Electrostatic ear speakers.


Type: All-stage FET configuration DC amplification driver unit.
Frequency response: DC – 100kHz (with one SR-009S).
Gain: 60dB.
Harmonic distortion: 0.01% or less (1kHz/100Vrms output).
Input impedance: 50kΩ (RCA), 50kΩx 2 (XLR).
Maximum output voltage: 450Vrms (1kHz).
Bias voltage: PRO 580V.
Operating temperature / humidity: 0 to 35 degrees C / less than 90% (non condensing).
Input terminal: RCA x 1, XLR x 1.
Output: RCA parallel output terminal.
Power consumption: 46W.
Dimension: 240W x 103 H x 393 D mm (maximum protruding portion included).
Weight: 6.3kg.

Type: Push-Pull Open Back Circular Electrostatic Headphone.
Frequency Response: 5 – 42,000Hz.
Electrostatic Capacitance: 110pF (including cable).
Impedance: 145k Ω (including cable, at 10kHz).
Sound Pressure Sensitivity: 101dB / 100V r.m.s. 1 kHz.
Maximum Sound Pressure: 118dB / 400Hz.
Bias Voltage: 580V DC.
Left & Right Identification: “L” and “R” indicated on the arc assembly (inside head spring) Left channel cable is marked with a solid Line. Right channel is marked with a dotted Line.
Ear Pads: Genuine Lamb Leather (direct skin contact), high-quality synthetic leather (surrounding portion).
Cable: Silver-coated 6N (99.9999%) OFC parallel 6-strand, low-capacity special wide cable, 2.5m full length.
Weight: 1lb without cable / 1.3lb with cable.

Build and finish:
Opening the box for the SR-009 I knew I was in for a treat when I saw the large engraved wooden box.
Within the box are what I can only describe as an exquisite pair of ear speakers. ( Oh the amount of times I’ve typed “headphone”… ).
The craftsmanship is elegant and classy. These ear speakers make a statement in design.
You can see and feel the countless hours that have been spent to get the aesthetic just right with a flawless finish.
The cups have a wonderful mix of a polished concave surround, bordered with a satin ( sand blasted? ) housing. The grills are a fine black metal mesh that feels sturdy, looks fabulous and contrasts well against the silver metal cups.
The headband is one little concern. Where the headband attaches to the adjustable sliders the connection feels delicate and I find myself being very mindful of this and always taking extra care when putting the SR-009 on my head.
STAX have made a cable that is very unique compared to anything else I have owned or demo’d. A flat ribbon style cable, It is robust in its build and doesn’t tangle. it and the extension cable both have a gold line running along one side of the cable making it difficult to plug it in the wrong way around. Saying that the 5 pin connector only connects one way. The plugs are solid and plug in firmly. I found no audible microphonics.
Coming next to the SRM-700S Driver, there is no wooden presentation box this time.
However the SRM-700S more than makes up for this in it’s appearance and finish.
The driver is big! and it’s heavy. Sat on my hi fi stand the SRM-700S stands out with it’s clean lines, the almost champaign tinted silver metal housing. It reminds me of high end hi fi gear that I would drool over when I was younger during the late 80’s into the early 90’s The front panel has a simplicity about it, easy to understand markings and a subtly chamfered split volume/balance knob that is smooth in its operation and feel.
The power button is rounded and smooth and has a good solid “Clunk” when pressed or depressed.
Going around to the rear of the driver we find a panel that is laid out well. The inputs and outputs are clearly labelled, offering ease of use.
We also find two selector knobs on the back panel. One to switch inputs and the other to select either internal or external volume control. Both have a solid click. I’ll get into that in more detail later though.
All of the components used in the SRM-700S are very high quality, for example, the volume/balance control is extensive on the inside and it shows in it’s use.

Setting the STAX system up is straight forward and simple.
With the rear and front panels being clearly labelled you will be up and running in mere minutes. However, I will recommend for safety reasons that you read the documentation. Electrostatic ear speakers work very differently from regular dynamic or planar magnetic headphones and the amplifiers that drive them.

In my system I run both a DAC in pre amplifier mode and a phono stage directly to the SRM-700S. The DAC sends a single ended signal and the phono stage is sending a fully balanced signal.
The SRM-700S’ volume can be controlled with it’s onboard volume control or it can also be switched to “external”, bypassing the internal volume control and allowing an external pre amplifier to control volume, essentially working like a power amplifier. I use it in this configuration so I can utilise the Conductor 3X Performance’s remote control.
I found no difference in audio quality, control or levels when using the system in this manner.
Note: the onboard volume knob is split into two knobs, one in front of the other.
One controls the left channel and the other the right channel.

Moving on to the SR-009 ear speakers comfortability.
I’ve owned and reviewed a lot of headphones from budget to high end. DJ, Studio and Audiophile alike.
The SR-009 are by far the most comfortable pair of over ears I’ve had the pleasure of using.
The ear pads are sumptuous and feel luxurious over my ears. They are soft and cushiony.
I experience no heat or sweatiness, which I have known to be an issue with other headsets.
My ears don’t come into contact with the “staters” as the ear pads are deep.
There is some weight to the SR-009, however it doesn’t translate directly to the wearing experience. STAX have designed these to sit comfortably on the head in a way that distributes the weight so it isn’t noticeable. I also notice almost no clamping force. In my experience I believe the weight of the SR-009 achieves the same effect. The headband is soft and forms to the top of my head perfectly.
Little positioning is required to get the required or correct sound.
I found I could wear these for long hours of listening time with no discomfort or fatigue. If they weren’t so heavy they would easily make the “disappears on my head” list!

Wearing the SR-009. Note the Sony MDR-SA5000 in the background.

And here we are. There are no direct comparisons here as I have no other experience with electrostatic gear at this point.
However I found it important to at least compare this system to my highest end and favoured headphones. The Sony MDR-SA5000. I currently drive the SA5K’s with either the Conductor or the Schiit Jotuneheim. Both fully balanced DAC/Amps.
Where the SA5K are clinical, finely accurate, fast and slightly on the bright side, the STAX SR-009 driven by the SRM-700S take all of these qualities, not including the SA5K’s brightness and heighten them, expand on them exponentially and prove their worth in every detail.
I mention the SA-5000 as I enjoy their fast paced accuracy and almost clinical detail.
They are my favourite headphone and so far nothing has come close to how they perform.
They do lack in the lower frequencies out of the box, however with a few tweaks I have remedied this by using aftermarket ear pads and a fully balanced re cable.

The STAX SR-009 have been heavily tested at The Audiophile Cafe. I have played every genre I enjoy for several hours each and the SRM-700S/SR-009 take every track in their stride.

A spacious expanse for a soundstage with depth and headroom that separates the SR-009 from anything I’ve heard before. Instrument separation is on point and definitive.
The signal from the SRM-700S and SR-009 is silent. In quieter passages of tracks I find a dark void of silence that gives a nice contrast to the music.

They are a dynamic ear speaker from the low end right through to the higher frequencies.
They do lack in sub bass, however it is present and has texture and detail. From there, I hear a full bodied, articulate low end that performs with immediacy and a hard hitting punch. Mids are smooth and airy, capturing and reproducing vocals in a manner that puts the vocalist in the room with me. Highs are fast, detailed and shimmering with a depth that I’m not used to in the higher frequencies.
Together with the aforementioned soundstage and separation the SR-009 and SRM-700S deliver a perfectly balanced, super-detailed sound with a liveliness and presence that will have you struggling to pull yourself away.
They are a fabulous all rounder, managing to play every genre with precision and grace.
One thing that stood out was their ability to perform heavy rock/metal better than anything I’ve experienced before. A lot of gear I’ve listened to over the years has struggled, especially with the harder metal that I like to listen to. The SR-009 and SRM-700S have no such difficulty, In fact I am noticing details in songs that I haven’t heard before. I also noticed how this system gives rock and metal more body and texture. So much so that I’m currently working my way back through my entire metal collection, joyfully rediscovering it as I go.
Classical and Jazz are a delight to hear and some classical works are quite a moving experience on the STAX. Electronica from the likes of Jean Michel Jarre and Depeche Mode are exciting and highly detailed. Studio recordings are clean and precise. Live performances are on a level that I struggle to put into words. They are truly that good.

Cost? I’ll admit, I’ve not worked with anything in this price point before.
$7,319 is a lot of money, ( includes the cost of the extension cable )
Is it worth it?
If I had the money in my bank to cover it, I would buy this system in a heartbeat.
The experience I have had with the STAX SR-009 and SRM-700S has been eye opening and life changing. Again, I struggle to find the words to convey how I feel about this system.
It’s like driving a perfectly brilliant Mercedes daily drive throughout your life, then swapping it out for a Ferrari.
I’ve heard some truly fantastic headphones, IEMs and speakers, at home, shop demos and at shows. And I’ve been blown away at times. None of it prepared me for the STAX.
Is it an “end-game” system? IMO? no. It’s close and very well could be for some, however, there are higher end drivers and ear speakers that could appeal to those looking for something further up the electrostatic chain.

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Thank you to Qobuz for continuing to supply The Audiophile Cafe with some truly remarkable music!
And thank you to STAX Audio for making this article possible, not only that, but also for sponsoring The Audiophile Cafe. I truly appreciate the level of support and help you have given to me and the blog!