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Stax Sigma - how many owners are left out there? - Page 3

Poll Results: What's your Sigma model?

This is a multiple choice poll
  • 56% (9)
    Normal Bias 6 Pin
  • 56% (9)
    Pro Bias 5 Pin
  • 18% (3)
    404 Modded Pro Bias with original drivers replaced by Lambda's
16 Total Votes  
post #31 of 110

those tweaks sound interesting.....

post #32 of 110
Quote:
Originally Posted by Tus-Chan View Post

 

Honestly, I'm glad you provide full disclosure. However, it would be nice to know without reading half of the review beforehand. Since you're obviously aware it's controversial, you should be aware that someone who doesn't believe in it, whether it works or not, would find it pretty damaging to the credibility of a review about the nitty gritty differences between three very similar pieces of gear.

 

Sorry if that's mean or rude, but that's just the way it is.

I can't think of much in audio which isn't controversial to someone or another.  It's a hobby not a religion so don't get too hung up.. There's a lot of things I didn't believe until I tried them.  I take everything with a grain of salt until I decide about these things myself.A good stat system is  sensitive to just about anything you do upstream. Sometimes,  the sound is made better, sometimes worse, sometimes just vaguely different and neither better nor worse.  People need to figure these things out for themselves.

 

Many tweaks such as CD polishes are inexpensive compared, say to a new cd player and are a very cheap way of exploring what matters to good sound.

 

 In the end audio is  subjective, it is not important what your peers think but how much you like something. But you actually have to get out there and do your own experimenting and listening.

 

BTW, I  wouldn't characterize low bias and high bias sigmas as "very similar"  although there is a family resemblance.  While I think some low bias phones are still pretty good, there are good reasons why Stax ditched these designs and now goes exclusively high bias, some of which are given in my review.

post #33 of 110
Thread Starter 
It's very kind of you to post your impressions of the 3 sigmas edelstrow. There can't be found many who have all 3 which gives you an invaluable contribution to the proceedings. Now, I must ask you one more thing; have you tried to listen to your pros through the normal bias 6 pin connector of your 717 or t1? I am using a 6 pin energiser and have not had the opportunity to try my pros on a pro energiser.
I would be extremely grateful if you spent 5 mins having a test through your normal bias then plugging in to the pro bias and seeing whether there's a difference.
post #34 of 110

 The Stax Sigma series panoramic earspeakers.

1. Models and nomenclature

The Stax SR-Sigma panoramic earspeaker was introduced in 1977. There have been 3 versions officially released and 1 after-market version commissioned.

1.     The original low bias, grey grille 1977 Sigma model (bias voltage of this model being 230V or “Normal”). The 2 um thick driver used was later recycled in the very successful Stax Lambda Semi-Panoramic earspeaker. The first release Sigma had a fabric coated, round bodied “kettle type” cord that connected the earspeaker to its amplifier/transformer and the grilles on this model are grey.

2.     Later versions of the normal bias Sigma (1987) used a lower capacitance, flat black cable that was recycled back from the (then) current Stax SR-Lambda earspeaker.

3.     The later Sigma Professional (1987) version introduced the 580V Professional 1um driver then used in the Stax SR-Signature earspeaker. This earspeaker had black grilles, lower capacitance chocolate coloured cables (from the Stax lambda Signature), and a chocolate coloured headband, compared with the original black cables and headband.

4.      A later version, the Sigma/404, is a Sigma rebuilt with high bias SR-404 1.35 um drivers and their corresponding very low-capacitance cables.

2. History and conception.

The Sigma earspeaker design was the result of a complete reassessment of how headphone sound is perceived. Up until that point, listening to headphones or speakers were considered completely different experiences. Headphones were designed to inject sound directly into the ears with as much sound isolation as possible between channels and also from the external environment, reflecting their communications genealogy. The drivers were parallel to the pinnae (= ear flaps) and either intra-aural, circum-aural or supra-aural.

Speaker listening has the drivers at a great distance from the ear canals and sound produced has to traverse a great number of direct, reflected and partially absorptive pathways before arriving at the ear canal, allowing much more modification of the sound, as well as left and right channel blending. The drivers are also in front of the listener and roughly perpendicular to the plane of the pinnae.

Naotake Hayashi, the genius behind the original Stax company, decided that one of the differences between speaker and headphone listening was a result of that very isolation and direct aural injection inherent in the design of all prior headphones. He decided to make a headphone that would actually sound like listening to speakers in a partially reflective/absorptive room. The genius lay in his recreation of a room around each ear – a revolutionary concept that has never before or since been replicated. Each ear-cup was meant to approximate a partially absorptive and partially reflective series of surfaces for the headphone driver (now in front of each pinna and perpendicular to them, as per speaker listening) to bounce sound off and then into the ear canal. In other words, the direct injection principle was thrown out the window and now the drivers were only heard after firing sound into the ear canals via a reflection - and some absorption – from an internal lining of mineral wool. I am guessing that the ear speaker cages had to be constructed pervious to air, rather than designed with a solid body, for weight considerations (viz. a solid body construction would have been too heavy for comfortable wearing). Possibly there were also enclosed cavity effects to deal with if the headphones were sealed. Indeed, weight has been one of the main complaints levelled at the only enclosed Stax design, the Stax SR-4070 Monitor. The mineral wool lining of the cages, apart from reflecting and absorbing sound, much like a normal listening room, also provided some hermetic sealing of the cages allowing reduced front to back sound cancellation around the periphery of the drivers. In other words, the drivers could have bass (the lack of which has been a criticism of the relatively similar design AKG K1000), but not as much as if a solid body had been used. I am guessing that a solid body Sigma had been tried and discarded due to comfort and sound considerations, so a compromise between weight of the headphones, sound quality and bass extension was reached.

3. Comfort.

The Sigmas, although bulky and laughably unfashionable, have been engineered to be exceptionally comfortable on your head. It is literally easy to listen for hours without your pinnae contacting the metal inner grille of the drivers (Lambda series) or the earpads themselves (SR-007). They also seem to be much cooler in summer than either of the above.

4.Sound.

a. Low bass and bass.

The sound of the Sigma always has slightly reduced very low bass because of some residual front-to-back driver cancellation through the mineral wool earcup lining, but beyond that point, the earspeaker’s sound is very hard to fault compared to what one is used to. The bass that is present, until the very low bass roll-off, is of excellent quality. It also packs a wallop (in both pro versions of the Sigma being discussed), which is quite unusual for an electrostatic headphone. Oddly enough, that wallop isn’t quite as evident in the Lambda Nova Signature, which uses almost identical drivers.  Certainly there are no bass instruments that move back and forward in the sound-field, nor do they completely disappear as they descend the scale, as I heard with the Jecklin Float Electrostatics playing, for example, Tony Levin’s descending Stick run during Projekct One’s “Live At The Jazz Café” Track 3. On the Jecklins, Tony appears to walk out the studio door as the run descends to subterranean levels. On the Sigmas and the Lambda Nova Signature, he’s in the studio and hasn’t moved a muscle.

              b. Midrange.

The reproduction of vocals comes as close to free of sibilant emphasis as possible.  This is truly what you hear in live, unamplified music.  Particularly realistic are piano and voice – the smoothness of the sound is just as relaxing on replay as it is live. Indeed, after attending a piano concert in a relatively reverberant wooden hall, the Sigma/404s got the extreme dynamics of the piano without any of the brightness at higher volumes that the Lambda Nova Signature exhibited.  The LNS is supposed to be bereft of the treble “sting” of the Lambda 404, so the 404 would be far too bright for me, despite the same driver performing beautifully in the Sigma/404. This exquisite piano/vocal reproduction is unique to the Sigma series, in my opinion.

 

             c. Treble

The later substitution of the 580V “Professional” bias drivers (either the Lambda Signature or the Lambda 404 headphone driver) to replace the original “Normal” bias driver, along with an upgrade of the original headphone cable, allows a reduction in the marked high frequency roll-off and a flatter extension to the very low bass reproduction compared with the original low bias Sigma. In my opinion, there are no drawbacks to this modification whatsoever and the top end sounds both smooth and evident, rather than smooth and rolled off as in the original Sigma

            d. Correct volume level.

 The Sigma/404 really shines a light on just how successful Mr Hayashi’s earspeaker design concept really is. Another bonus I have noted with these earspeakers is that it seems to be relatively easy to dial up the “correct” volume of sound – they just sound “right” at that point. Although this is not unique for these phones, I haven’t heard a headphone with such a pronounced “correct” volume level for a track. The bass and treble just seem to be in perfect balance with the midrange only at that volume. Peter Walker of Quad was a great proponent of the “correct” volume theory apparently. Strange that I also have Quad Electrostatic speakers.

            e. 3-D sound.

Then there is the seemingly increased 3D space that these headphones portray – the sound stage seems to be actually in front of the head, with some front to back space, compared with the usual line-between-the-two-ears imaging. This is something I’m not as good at hearing, so I will leave it to others to give their impressions.

These differences allow greater appreciation of albums that were mixed for speakers in the standard control room, because that is exactly what the Sigmas replicate.  I would guess that apart from very low frequency roll-off, these earspeakers could be the greatest and most accurate magnifying glasses for mixing evaluation ever made.  They have in built room diffusion, diffraction and absorption effects without the left to right blending, so that each channel can be easily heard independently.

 

5. Associated equipment needed.

I have found the Stax SRD-7 Pro, SRD-7 Mk 2, or SRD-7 Spritzer will do an admirable job of driving these very power hungry monsters, provided a good power amp is pushing them. Here, I use the Studer A68 power amp fed by an Apogee Mini-DAC and a Studer D730 CD player. If you wish to drive them with a direct drive electrostatic amp, I would suggest, at the very least, using any of Stax SRM-717/SRM-727/SRM-T2, Kevin Gilmore/Spritzer’s revamped T2 or the Blue Hawaii SE/Solid State Electrostatic amps. They are all powerful enough to drive these and the SR-007 Mk1/Mk2 series. The Lambda series are far less power hungry, despite using the same drivers as the Sigmas. Distance from the ears and absorption by the damping material may both account for these efficiency differences. The volume control levels for the Sigma/404 and SR-007 Mk1 I once owned were identical for the same reproduced volume – i.e. they seem to be equally inefficient - compared with a Lambda Nova Signature.

6. Credits.

Finally, one has to admire a designer who actually truly said nay to any marketing considerations. These phones are laughably big and ugly, but if they were anything else, could they sound as good? Thank you, Mr Hayashi for not listening to the form-over-function naysayers, and I bet there were plenty of those in Stax board meetings in 1976/1977

Lastly, I would like to thank Edstrelow for the inspiration to upgrade my Sigmas to Sigma/404s – something I did on faith and have never regretted it for a minute, and Webbie64 for making me realise the error of my ways when I briefly thought about selling them.

7. Postscript - Stax Sigmas: high bias earspeakers compared – Pro vs Sigma/404.

The 2 Sigma high bias phones essentially differ in 2 main physical ways.

  1. The headphone cable used for the original Sigma Pro was the same as the one used on the Lambda Signature – not as wide as the one used for the Sigma/404 hybrid, which was first seen on the Lambda Nova Signature.
  2. The drivers are different also – the Sigma Pro uses the reported 1 um Lambda Signature driver, whilst the Sigma/404 uses the (2 generations) later 1.35 um drivers first seen in the Lambda 303/404.

 

Otherwise, the shells of the 2 earspeakers, apart from minor colour variations, are identical. The Sigma Pro driver appears to be very slightly more efficient than that of the Sigma/404.

In my set up so far, the two have been compared through

  1.  Studer D730 -> AES-EBU digital outputs -> Apogee Mini-DAC ->  Studer A68 -> Spritzer Pro SRD-7 bias + transformer box.
  2.  Studer D730 -> analog XLR outputs -> Stax SRM Monitor direct drive earspeaker amplifier.

 

Both chains give repeatable results.

As seems to be the order of the day, the results are not what I expected.  The Sigma Pro is far better than its reputation suggested and even bests the Sigma/404 in a couple of areas.

Firstly, the deep bass is slightly more evident and the mid bass is much tighter and slightly less resonant. In the Sigma Pro, bass drum has slightly more punch rather than smeared thud. Deep bass has been one of my only criticisms of the Sigma series. This is the best I’ve heard it, but only by a hair’s breadth over the Sigma/404.

The midrange is about the same with both, but the treble is slightly more evident with the Sigma Pro. It’s close to a line call there, however.

As for dynamics – the Sigma Pro does dynamics somewhat better than the Sigma/404.  The Lambda Signature driver/cable just sounds a little faster than the 404 driver/cable. This tends to alleviate some of the complaints about a mushy low end of the Sigma series.

The original Sigma low bias was far too rolled off at the top end in particular, despite the magical Sigma midrange being present there. It appears that either the Signature or 404 driver implants are a successful remedy to this, and give a phone that had huge promise a push into reference territory.

In summary, despite every single report to the contrary, I’m loving the Sigma Pro! Flame suit on, hearing aid batteries fully charged LOL. Stax SR-009? Who cares?

post #35 of 110

Another Crimsoner! Love it!

post #36 of 110
Quote:

 

            e. 3-D sound.

Then there is the seemingly increased 3D space that these headphones portray – the sound stage seems to be actually in front of the head, with some front to back space, compared with the usual line-between-the-two-ears imaging. This is something I’m not as good at hearing, so I will leave it to others to give their impressions.

These differences allow greater appreciation of albums that were mixed for speakers in the standard control room, because that is exactly what the Sigmas replicate.  I would guess that apart from very low frequency roll-off, these earspeakers could be the greatest and most accurate magnifying glasses for mixing evaluation ever made.  They have in built room diffusion, diffraction and absorption effects without the left to right blending, so that each channel can be easily heard independently.

 

 

Actually pure stereophonic headphones have always failed to reproduce the Imaging of a pair of loudspeaker because of lack of HRTF (Head related transfer function). It's because of the shape of our anatomy that our brain can localize sound horizontaly and verticaly.

 

In short both our right and left ears receive sound pressure from a single speaker, and it's because of that that we can localize it and that the holographic stereo soundstage can be understood by our brain. In headphone, the Sigma inject sound only in one ear at a time.

 

You might know the Smyth system, it's a dsp around the HRTF phenomenom.

post #37 of 110
Quote:
Originally Posted by telecaster View Post

Actually pure stereophonic headphones have always failed to reproduce the Imaging of a pair of loudspeaker because of lack of HRTF (Head related transfer function). It's because of the shape of our anatomy that our brain can localize sound horizontaly and verticaly.

 

In short both our right and left ears receive sound pressure from a single speaker, and it's because of that that we can localize it and that the holographic stereo soundstage can be understood by our brain. In headphone, the Sigma inject sound only in one ear at a time.

 

You might know the Smyth system, it's a dsp around the HRTF phenomenom.

 

 

 

 

 

Except for the fact that loudspeakers don't image as well as headphones.  Directional hearing is based on time and amplitude differences at the ears. In fact for most stereo listening only the amplitude differences matter.  This what you fiddle with when you use a balance control or less commonly a channel blend control.Loudspeaker imaging is what is poor because it creates artifactual phantom channels which mess up both the time and amplitude differences. 

 

Very simply, you have 2 ears, each having a different perspective on sound, with signal time of arrival differences and more importantly interaural amplitude differences between the ears. If you record sound with 2 microphones some distance apart you will capture  time and amplitude differences.  Play this sound back by headphones and you get a reasonable approximation of what you would hear if you had been in the recording situation.  If you want  more accurate headphone sound you use a dummy head to get the precise interaural  time and amplitude differences of an actual head  as well as some subtle head effects such as shadowing and pinna effects.  Only the latter are, I believe are correctly called HTRF.

 

Why are speakers bad for imaging? Because each channel now feeds both ears.  The left channel feeding the right ear and the right channel feeding the left ear are called phantom channels.  They have no reason to be there, they are simply ARTIFACTS of speaker listening.  Headphones don't have such artifacts. And they are huge artifacts as loud as the main left and right channels, think of them as 100% distortion.  However the ear and brain are still able to make some sense of this speaker rubbish probably because of the "precedence effect" in which the first arriving time signal tends to "set the stage for direction with the latter (phantom) signal being fused into it and you hear an approximation of stereophonic sound but not as accurate as if the phantoms were not there.

 

Various  systems have attempted to correct this problem with speakers.  I have a set of Polk SDA1 speakers which generate  cancellation signals to get rid of the phantom channels so that you hear 2  rather than 4 channels. . It's a reasonably effective process and greatly enhances stereo speaker imaging at least over modest sweet listening spot.   

 

 I have not heard the Smythe system but I believe it is an attempt to allow an engineer to monitor by headphones as if one was listening to speakers and it attempts to recreate speaker sound for headphones. Other than recording engineers I can't imagine why anyone else would want such a setup.  It is not trying to recreate the original soundfield, which is the usual goal of Hi-Fi,  It's trying to recreate the speaker soundfield with all its imprefections and if you want something like surround sound through headphones, Dolby Headphone is pretty good and a lot cheaper.

 

 

 

 

 

 


Edited by edstrelow - 7/1/13 at 12:43am
post #38 of 110

H John,  

 

I certainly agree that one can be perfectly happy with the Sigma pros or Sigma/404 over Stax' more recent flagship phones such as the 007 at least, since I have not heard the 009.    When I tried the Sigma/404 with a top amp such as the BHSE this  was even more the case.  But I would note that you are using transformers to run your phones and I and most others are using amps. For me these are the SRM1Mk2 and 717. I note that my low bias transformer really changes the sound balance of  my low bias phones vs the amps I have.  So you may very well get a better sound with your Sigma pro than the 404 with this set-up.  I certainly can't contradict that.  But with amps I find the advantage  goes the other way.  I set up my pro and 404 together a few years back at the LA Canjam and many people commented on the virtues of the Sigma/404 over the pro.  Still they are both great phones and not as different as, say the pro and the low bias Sigma.

post #39 of 110
Thread Starter 
Hi John, thanks very much for your analysis, I already decided I would not be changing my drivers for 404s no matter how easy that was to do. This just confirms how good the pros are. I still wondfer whether I am getting the best from mine with my SRD6 normal bias energiser but it sounds better this way than through the 252S. There's room for improvement for sure. But for the mean time they're great!
post #40 of 110

@John - as usual it appears you have a very intimate knowledge of all things to do with the Stax Sigmas. Thanks for your impressions!

 

Quote:
Originally Posted by edstrelow View Post

But I would note that you are using transformers to run your phones and I and most others are using amps.

 

In §7 of his post John mentions his extremely rare SRM-Monitor (which is like an SRM-1 plus a diffuse field equaliser).

 

Quote:
Originally Posted by Takeanidea View Post

Hi John, thanks very much for your analysis, I already decided I would not be changing my drivers for 404s no matter how easy that was to do. This just confirms how good the pros are. I still wondfer whether I am getting the best from mine with my SRD6 normal bias energiser but it sounds better this way than through the 252S. There's room for improvement for sure. But for the mean time they're great!

 

Too lazy to try it myself but I'm pretty sure your pair of sigma pros would sound much much much better from a pro socket compared to a normal bias one for obvious reasons.


Edited by jjinh - 7/1/13 at 1:38am
post #41 of 110
Quote:
Originally Posted by jjinh View Post

In §7 of his post John mentions his extremely rare SRM-Monitor (which is like an SRM-1 plus a diffuse field equaliser).

Heh? SRM-1? You mean SRM1- MK2? This and SRM-Monitor + the Lambda Pro was suppose to make it sound more neutral. I have the SRM-1 and it is anything but a SRM-1 MK2 although it sounds very close in areas.

post #42 of 110

Stax SRM-Monitor

 

Overview

 

The SRM-Monitor is a combination of Stax' solid-state amplifier, the SRM-1 Mk2 Professional and their diffuse field equalizer, the ED-1, in one larger package. The SRM-Monitor came to the market in 1988 and was still available in 1995, according to the Stax 35th Anniversary product brochure. The volume control of the SRM-1 Mk2 appeared to have been changed to a dB calibrated numbered type with indents, for repeatable and measurable volume variations in a professional situation, but internally the same blue ALPS RK-27 dual channel potentiometer had been used. Most of these units appear to have been sold to audiometry workplaces, as they are quite often referred to in research papers, and rarely mentioned or seen elsewhere.

 The two inputs mentioned below are switchable between either balanced or single ended (via two sliding switches on the back panel – one each for left and right channels), and the diffuse field equalizer can be switched on or off via a push switch on the front panel. These units seem to be extremely rare (I have seen as few of these for sale as the Stax SRM-T2 over the years).


Inputs on the back panel consisted of:


1. 1x Unbalanced line level RCA/cinch input.

2. 1x Balanced line level XLR/Cannon input.


Outputs consisted of:


1. 1x Unbalanced RCA/cinch loop output (with the Diffuse field equalizer output switchable) – back panel

2. 2x Professional bias headphone jacks (580V) Stax 5 pin connector – front panel.

3. 1x Normal bias headphone jack (230V) Stax 6 pin connector – front panel.

 

History

 

Headphone frequency response measurements, conducted with a microphone in front of the headphone driver, much as speaker measurements were conducted, observed that headphones with a measured flat frequency response did not sound as flat as would be expected from a speaker with identical measurements. Comparing the sound of a flat measured speaker with a flat measured headphone revealed extreme tonal differences that started off a whole lot of investigation into why they sounded different and how a headphone’s frequency response could be altered to make it sound like flat measured speakers.

An experiment was set up as follows:

1. A loudspeaker playing a frequency sweep was recorded by a high quality, miniature microphone in one of two types of room – either an anechoic chamber or an approximation of an ordinary room (see later) – and the frequency response was charted.

2. The same microphone was inserted into a subject’s ear canal and the same speaker replayed frequency sweep was charted again.

3. It turned out there was quite a difference between the charted frequency response of the two recordings.

4. It was postulated that if the frequency response of the recording made by the microphone in the ear (see 2) could be altered by pre-equalization to ultimately match the shape of the frequency response of the recording of the same microphone when not in the ear (see 1), then replay of that in-ear microphone recording would sound the same as that of replay of the recording made by the same microphone in a room.

5. This gave rise to a target measured frequency response for a headphone to sound like a flat measured speaker i.e. if the headphone had a measured frequency response that looked like the target response, it should sound flat when reproducing a recording that had been mixed with speakers in front of the mixer, and sound as if one was listening to speakers in front of him/her, rather than via headphones.

6. The concept of pre-equalization of headphones was thus born.

 

Pre-equalization could either be mechanical (i.e. the driver frequency response was manufactured to behave that way e.g. the AKG 240DF – not so easy) or electrical (which should be cheaper, easier, field-adjustable and possibly adaptable to different headphones), and meant that although the headphones now had a frequency response that had been altered to something that looked decidedly non-flat when measured, it reproduced the sounds coming from a sound source with the same frequency response at the ear canal as if recording and replay over headphones had not been introduced into the chain i.e. the headphone replay should now sound the same as sitting in the room and listening to the speakers.

Two main theories of the correct pre-equalization curve were forwarded. The first, called free-field equalization, suggested that the above experiment be conducted in an anechoic chamber (like a field, free of reflective, absorptive and refractory surfaces). So, to reiterate, a free field equalized headphone is designed to sound like the reproduction of speakers with a listener sitting in an anechoic chamber. Although an anechoic chamber is more reproducible as a standard, it was argued that nobody listens in an anechoic chamber (and indeed, most listeners find even speaking in an anechoic chamber uncomfortable) and a reasonable approximation of a standard listening area be used to conduct the above experiments. This was called diffuse field equalization.

There are many things that alter sound between the release from the sound source and arrival at the ear canal. Reflections, diffraction and absorption from objects in the listening environment, reflection, diffraction and absorption by the head, hair and ears all contribute to alteration of sound before it reaches the ear canal. Diffuse field equalization, as mentioned before, is an attempt to make the replay of a recording on headphones sound like you are listening to the same recording through speakers in a non-anechoic room. Experiments were also done so that headphone users were asked to equalize various sharply limited frequency bands’ playback on headphones until they had matched the loudness of the same playback through speakers and with headphones removed. A good correlation was obtained between this method and the probe microphone recording method.

The direction of sound (from the front in a reverberant field) with speakers is far removed from actually injecting the sound directly into the ear canal. Naotake Hayashi (of Stax), pondering this problem, possibly because Stax couldn’t successfully mechanically create a diffuse field equalized headphone, and any electrical equalizer would have to be a custom unit, first decided to create a new headphone that coupled its own reproducible miniature room (complete with uneven diffractive, reflective and absorptive surfaces) called the Stax SR-Sigma Panoramic Earspeaker System. It had headphone drivers that fired from anterior to posterior instead of laterally into the ear canals. The sound was bounced off irregular mineral wool into the ear canals, creating a mechanical diffuse field room for each ear as well as having "speakers" that fired sound from the front, rather than straight into the canals. It was partially successful, but listeners either hate it or absolutely love it. Personally I have always loved it, but they are quite inefficient headphones and also sounded quite rolled off at both ends of the frequency spectrum. They were also huge and very odd looking. Better drivers than the original Sigma drivers (which were later recycled into the Lambda non-professional earspeakers) improve the frequency extremes, allowing the merit of the theory to finally shine through (e.g. the very rare Sigma Pro or the Sigma/404 hybrid provide the sound that the Sigma gave a hint of).

Stax later decided (around 1986 – 1987), instead, to bite the bullet and build 4 custom equalizers to electrically equalize their latest headphone range to provide individual target diffuse field responses for each of its various, then-current headphones (the ED-5 for the SR5 normal bias headphone, the ED-1 and SRM-Monitor for the Lambda Professional high bias phone and the ED-Signature for the high bias Lambda Signature). The headphones could then be less bulky than the Sigma and more fashionable (see my avatar for what the Sigma looked like – it definitely had a style only a mother could love). Again, reactions to Stax engineers’ diffuse field equalized headphones literally polarized listeners into “hate it” or “love it” camps. I would guess that economically, this proved to be a dead end, and no further research into diffuse field equalization has ever been mentioned by Stax. Consequently, the rather rare equalization units sell for a premium on the used market these days.

 

As mentioned above, the four ED diffuse field equalizers were designed for three different Stax phones. The ED-5, ED-1 and ED-Signature were placed between the source and the headphone driver and are connected by way of RCA cables. The ED-1 matched the construction and size of the SRM1 Mk2 Professional and was finished, like those units, in either black or silver. The ED Signature matched the chocolate brown of SRM-T1/S/W. The SRM-Monitor incorporated an ED-1 and an SRM-1 Mk2 Professional into one large package and was finished in either black or silver, and had switchable RCA or XLR inputs. The ED-5 unit was made to match the then current SRD-6 transformer unit (an interface between a speaker-driving power amp and the Stax earspeakers) in silver.

The ED-Signature would most likely also match the 404 and Lambda Nova Signature. The ED-1 equalization (in my case, provided by the SRM Monitor) sounds excellent with the Lambda Nova Signature and surprisingly good with the Omega 2 Mk 1, despite being the wrong equalization for the latter. The upper midrange/lower treble, in particular, sounds quite a bit flatter and the low end remains in good balance with the mid and high. As Bill Sommerweck said in his review of the ED-1 in the April 1989 issue of Stereophile, track 9 on Stax' own “Space Sound” CD changes from objectionable (without the equalizer switched in) to quite listenable with the equalization switched in. In my opinion, there is no magical out of the head experience, except when listening to the aforementioned CD, or the Ultrasone binaural tracks (i.e. binaural recordings). These are seriously spooky, but sound 3 dimensional with or without equalisation. Try them with someone who is not used to listening to headphones and see what happens when you cue up track 1 or 2 of the former, or the fireworks track of the latter. Sabine whispering in your ear - oh yes! Shower spraying on your shower cap - OMG!

 

Now, here is where things start getting weird. I had a listen to the Sigma/404 and the SR-007 phones with the equalizer on and they both sound great - it may just be happenstance, but I've never heard "Kind Of Blue" sound so wonderful and with plenty of lower bass (which even the SRM-717 doesn't seem to match). This is strange, as the frequency response for the ED-1 is flat in the bass, and should not be suited to the Sigma/404 or SR-007 anyway (see graph below).

 

Stax ED-1 diffuse field equalizer, frequency response with EQ out (top) and in (bottom) 5dB per vertical division.

Maybe it's a de-emphasized treble spike? I don't know, but whatever, this pre-equalization is not just scientific theory and sounds really good. To me, the sound has gone from lots of good hi-fi parts and moved to an organic whole. To my ears, the Stax SRM-Monitor is the single best piece of equipment I have ever purchased.

 

General Description of the Sound

 

The SRM-Monitor, without the equalizer engaged, is a very good pure class A FET DC amplifier with clear dynamic sound and excellent low level detail resolution (indeed, under these circumstances it is almost the same as the SRM-1 Mk 2 Professional, apart from the added balanced input and the click stop calibrated volume control. There are apparent improvements to the sound, smoothing the slightly spiky balance of the SRM 1 Mk2 Pro. Compared to new Stax amplifiers, such as SRM-717, the sound is slightly less refined and on the dry side, but still very impressive. Stax tube amplifiers such as SRM-T1, SRM-007t etc might offer a little bit more refinement and are more fluid in their presentation as well but are not as powerful.

However, when the Diffuse Field Equalizer is switched in, this amplifier becomes magic. A reduction in any residual Lambda series tizziness in the upper midrange and a slight filling in of the Lambda midrange trough allows the Lambda to sound much flatter while retaining the power it is capable of.  Cymbal reproduction is particularly improved. The vocal reproduction is much better overall, coming closer to the nearly perfect Sigma series in that department. The bass quality is also flatter, which is odd, as the equalizer frequency response appears to leave the bass frequencies unchanged.

The SRM-Monitor also sounds great with the SR-007 Mk1, especially with the Diffuse Field Equaliser switched in, despite the equalizer being specifically adjusted for the Stax Lambda Pro. There is no hiss or hum at any setting of the volume control.

Pricing & Other Data of Interest

Used prices at the moment vary from $1000 to $1500 depending on version and condition. I have only ever seen 2 for sale in over 10 years and the one I didn’t buy had clearly seen better days.

 

 

Technical Specifications

 



Frequency characteristics: DC~20KHz ±1dB

Input impedance: 50KΩ

Amplification factor: 60dB

Distortion factor: 0.02%/1KHz/100V with Lambda Pro

Input level: 100mV

Bias voltage: 230V (normal bias) 580V (professional bias)

Electric power consumption: 47W

Size: (W) 300 mm × (H) 87 mm × (D) 314 mm

Production run: 1988 - 1995?


Edited by John Buchanan - 7/1/13 at 5:45pm
post #43 of 110

Interesting I looked at the SRM-Monitor as the ED-Monitor that was used to pair up with the MK2's + LP for a more neutral response. 

 

Now googling the SRM-Monitor, I have seen it once on for sale for 2000 euros around the time I joined here on the German ebay domain. Is that expensive?

post #44 of 110

I got mine for about US$1400 and it was as near mint as you could reasonably get. Over the years, I'd only ever seen very poorly maintained units until then. IMHO, it was an absolute bargain.

post #45 of 110

It should be pointed out that the SRM-Monitor is just a SRM-1 Mk2 and a ED-1 in the same box.  redface.gif 

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