Thanks to Mad_Economist of Cascadia Audio for loaning me his Stax SRS-2170 system to evaluate and review.
When people talk about electrostatic headphones, there is one brand that immediately comes to mind: Stax. Stax has been a manufacturer of premium electrostatic headphones for decades, with Koss being the only other company with an electrostatic headphone in their regular production line-up for remotely as long. Sennheiser released the electrostatic Unipolar series in the 70’s and released the HE-60 and HE-90 in the 90’s under the Orpheus brand. They also recently introduced the €50,000 HE-1. HE Audio was a short lived venture of Dr. Fang Bian, who later went on to create HiFiMAN and has recently come back to the market with the Shangri-La electrostatic headphone system. Other notable manufacturers of electrostatic headphones are KingSound, Dharma with its electret/dynamic hybrid, WarWick Audio, who OEMs electrostatic driver diaphragms, and Shure with the introduction of their first production electrostatic IEM system.
Electrostatic headphones are a very small niche inside the already niche hobby of headphones. They tend to be inaccessible due to their somewhat higher barrier to entry with low availability (often with the need to import the unit from Japan, which voids the warranty) and generally high cost compared to dynamic and planar dynamic style headphones being some of the major reasons. The Stax SRS-2170 is their entry-level system, and can go for anywhere from $500 to $1000 new. One of the reasons for this is that due to their driver design, electrostatic headphones need a specialized amplifier. The SRS-2170 is a headphone system-in-a-box, containing the Stax SR-207 “earspeaker” and the SRM-252S electrostatic amplifier. Due to the extremely small market that electrostatic headphones cater to, it has been hard to maintain a practice of building only electrostatic headphones, and seems to be a reason why Stax was recently acquired by the Chinese company Edifier.
The SR-207 is just one headphone from a line that has existed since 1979: the Lambda series. The first Lambda was made to be a more user friendly version of the very bulky Stax Sigma by using angled pads and a slightly angled housing. Stax still maintains much of the original Lambda design in its current L-series headphones, making it one of the longest-lasting product lines in the headphone industry.
Fit and Comfort
The SR-207 is not a comfortable-looking headphone. However the large ear cups fit my ears quite comfortably, the pads, though flat and thin, are firm and because of the light clamp are comfortable against the head. The headband design hasn’t changed significantly since the first Lambda series, with a suspension strap hanging between two friction adjusters on the headband assembly. It’s a bit tricky adjusting the headphones for your head, but once you have them set, the headphone is quite comfortable. The headphone is also extremely lightweight and if not for its size, could feasibly disappear on the head.
I find most electrostatic headphones, especially Stax, share an ethereal quality to their presentation of music. Sounds seem to appear from nowhere, they seem to softly float in space like “ghosts singing and playing ghost instruments.” Many people attribute this sound to the driver design, utilizing a super-lightweight diaphragm vibrating extremely quickly to reproduce sounds. Some people conjecture that this is due to the low weight and thickness of the diaphragm. I am not sure why this happens, but it is something I consistently observe regarding electrostatic headphones: they tend to lack a certain weight and impact to the attack of notes that creates the ethereal quality I mentioned earlier and to me is the main reason why headphone fans are divided on electrostatic headphones. The headphones have excellent clarity and sound quite detailed, but without the texture or weight, they have a sort of soft sound to them that detracts from the experience for me. Some people may find this airiness and weightlessness less fatiguing and a more relaxing listen.
The bass of the SR-207 is quite detailed and fast, able to convey all the individual peaks in sustained bass notes. However the headphone still lacks the fullness and body to really convey the sense of impact you can really feel with headphones based on other drive mechanisms. Overall, the bass seems linear with a slight dip in the midbass, that gives it very slightly subbassy tilt that adds to the headphone’s punchiness. The SR-207 really does well in terms of overall linearity and clarity, however it’s unable to convey the weight and texture that give headphones what I consider an additional layer of detail.
Mids on the Stax are very clean, again with very good clarity. Voices give me the impression of being detached and sort of floaty, which in my experience has been typical of the presentation of vocals and instruments for other electrostats. The SR-207 has a bump starting somewhere near 1kHz and going up through the upper mids, which makes female vocals especially stand out and can actually make them sound somewhat harsh. I found that when listening to female vocals, they tended to stand out in the mix and sounded louder than they were supposed to. Aside from the general lack of impact and texture to the music which is more of a characteristic of the driver, this harshness is probably my biggest issue strictly with the tuning of the headphone.
Treble is polite and, for the most part, I have no issues here. As with everything else, clarity remains good here, but the headphone lacks a certain kind of bite, with a treble presentation that may come off as overly smooth. This can be great especially for recordings that are especially harsh or unrefined here. The SR-207 does a great job of smoothing over harsher or grainier recordings, however it feels a bit too smooth and seems to lose out on some texture and detail in the treble as a result.
The Stax present a very large stage with very good imaging and separation of instruments. It’s very easy to use these headphones to analyze a lot of different aspects of a mix with these headphones–at least partially because of how fast the drivers are. The sense of space that these headphones can convey is very good, however, despite being able to image and stage well, the sources of sound seem to float rather than being grounded where they are positioned. From that perspective, it can be difficult to really get a hold on where things are in the space it presents, though it’s easy to tell where things are in relative position to one another.
Overall, I don’t have a lot to say about the Stax SR-2170 system. I think the SR-207 headphone is quite competent at delivering clarity, linearity, good imaging and separation. I don’t personally enjoy the mid-mid to upper-mid emphasis that makes voices a bit harsh and shouty, nor do I like the generally ethereal presentation because I feel it robs the music of some additional layers of detail. Other than those issues though, from a technical standpoint it’s a very well executed headphone with some characteristics I would call flaws but others would call strengths, which make it polarizing for headphone fans. The need to have a separate amp specifically for this headphone is also something to consider, though with the 2170 system, that has been taken care of with the SRM-252S, an amp that is small, but certainly seems capable enough not to be an issue.