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Used in conjunction with the SRM-006tII tube driver.

The Stax 4040II System is one of the few headphone systems I could envision displacing my loudspeaker listening. It achieves a few of the holy grail qualities headphones must have to warrant extended, repeated use:

1. Neutrality. These headphones are near perfect in their tonal response and as such are nearly fatigue free. The frequency extremes are decently extended which is a bonus, but most importantly, there are no errors within the range they reproduce. Some may find the lack of a mid-bass hump disconcerting, but after acclimatizing to the sound you realize this is how music is supposed to be reproduced.

2. Comfort. Other than the AKG K501, these are the most comfortable headphones I have ever used. You can wear them for hours and hardly notice them.

3. Openness of soundstage. Better than anything I've heard, these allow you forget at times that you are listening to headphones.

4. Supreme resolution. I have heard no headphones which better these in terms of low-level detail. Other headphones will force detail upon you through accentuated treble or emphasized transients. These present everything "as it is."

The few drawbacks of the SR404 are largely related to partnering equipment. You must search out the best source possible. I would hesitate to use any CD player below $3000. These are too revealing. The sound you may get won't be unpleasant as Stax always makes the best of the source material, but it will become painfully obvious what kind of flaws most source components suffer from.

I strongly recommend the SRM-006tII as it offers a "liquidity" and a touch of warmth that perfectly rounds out the SR-404.

Associated equipment at the time of review:

E-MU0404 (digital out)
Bel Canto DAC2
STAX SRM-313 energizer
STAX SR-404 headphones
Belden 1694 cable w/ Eichmann bullet cu connectors


The SR-404 is a very lean sounding headphone. It lacks an elevated midbass hump found in most headphones, and has a upper midrange/lower treble spike that makes them sound a bit unnatural for some recordings. However I think the SR-404 would make a sufficient monitoring tool, but your tastes would have to lie in the analytical domain if you wanted to use them strictly for music. The SR-404 have a "wow factor" to them that kept me very impressed for the first couple of weeks that I had them. But after that the lack of body kept me wanting a bit more. I'll break up this review into comparisons with with AKG K1000, then go over the individual breakdown for the SR-404.

Comparisons with the AKG K1000
I did multiple AB comparisons after receiving the AKG K1000, and overall I was more satisfied with the K1000, even under amped at the time. The K1000 improves upon nearly every aspect of the SR-404 while still being enjoyable and musical. The K1000 does have a slight midbass hump that makes them more enjoyable for rock and jazz music. The midbass is one of the K1000's very strong points. The SR-404 extends lower than the K1000, but not by much. The SR-404 bass is very airy that is very enjoyable with classical music, but left me wanting more for rock, jazz, and electronic music. The bass isn't as textured as the K1000, but still very nice allowing you to follow complex bass lines. Midrange on the SR-404 is very, very dry. Female and male vocalists sounded a bit dull and lacking in emotion, also the upper midrange spike made some recordings very sibilant; during my time spent with the SR-404 I used an EQ on my PC which helped a little. Upper frequency extension was fantastic and just as good as the K1000, I can't note many differences here. Overall soundstage was wide, but nowhere near the K1000. The SR-404 had excellent left to right separation, but not much top to bottom. The SR-404 also sound very 2-dimensional. The K1000 and STAX Omega 2 are the only "3-D" headphones I've heard so far. Still if you enjoy very fast note attack and decay the SR-404 will not disappoint. However they are unable to blend with the music. For passages that require long decay the SR-404 simply doesn't portray that accurately. For example classical music doesn't give you an accurate impression of the venue. Instead it sounds like you're just listening to the instruments and not the overall picture. Instrument separation and placement is excellent, and instruments further away are softer, and appear further away, however the lack of decay doesn't make imaging on the SR-404 go for that last bit of perfection.

Bass extension:
Not bad. Extends further than the K1000. I want to say it rolls off around 30 Hz, but I don't have the exact figure written down from when I used bass sweeps.

Bass impact:
Very poor. Bass is very airy, and lacks impact. Kick drums sound artificial, and doesn't have the oomph for rock music.

Bass quality:
Overall bass quality is above average. Bass is articulate, but not as textured as the K1000. Lacks a midbass hump that makes it more suitable for monitoring, but at the same time can make the headphones sound lean. On poorly recorded material bass can easily distort.

Midrange:
Average. Very dry with a upper midrange spike that makes some recordings sibilant.

Treble:
Above average. Extension is very good, and I didn't notice any unnatural treble sheen. Cymbal hits sound absolutely amazing. My only gripe with the treble is electric guitars have an unnatural hazzyness around the notes that sounds almost like a crackling. Especially evident on fast guitar playing like prog metal.

Soundstage:
Above average. Wonderful left to right separation, very nice for classical music. Just lacks top/bottom soundstaging, and still sounds very 2D like conventional headphones.

Detail:
Above average. Excellent micro detail, still I find the K1000 more detailed while not being too obvious about it.

Portability: N/A
Only works with pro bias amps. No pro bias portable amps out right now.

Isolation: N/A
Probably second worst next to the K1000. The stat diaphrams make these very open. More than normal open dynamics.

Comfort:
Above average. Very comfortable, large earspeakers cover a large area of your head and the headphone pads and headband are very comfortable. I did have to take them off to allow my ears to breath after about an hour of use, can get very hot with the pleather pads.

Durability:
Very good. Although all plastic they feel very solid. STAX makes the best cables I've ever seen on any headphone.

Improve with amp:
Can't comment, as I've only heard these out of the SRM-313.

Value for money:
Slightly above average. Requires an electrostatic amp which can not be used with dynamic headphones. Still the setup reviewed is up there with the best mid-tier headphones.


If you want a simple picture painted for you the SR-404 is the polar opposite to the HD650. At least to me 2 headphones could not be more different, however both are good in their own right. If you're thinking of getting the SR-404 you should definitely try and audition them. Because you might just love them, or you might hate them. For around $850-900 new the SR-404/SRM-313 isn't too bad. I prefer the K1000, but you're looking to spend that much on just the headphones. And building a system around them costs a lot more than the STAX.