The Stax Sigma series panoramic earspeakers.
The Stax SR-Sigma series was introduced in 1977 with the original low bias Sigma model (Bias voltage of this model being 230V – the driver used was later recycled in the very successful Stax Lambda earspeaker).
The Sigma earspeakers were the result of a complete reassessment of how headphone sound is perceived. Up until that point, listening to headphones and speakers were considered completely different experiences. Headphone were designed to inject sound directly into the ears with as much sound isolation as possible from the external environment, reflecting their communications genealogy. The drivers were parallel to the pinnae and were 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. The drivers are also in front of the listener and at an angle that is close to 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 room. The genius lay in his actual recreation of a room around each ear – a revolutionary concept that has never been replicated. Each earcup was meant to approximate a partially absorptive and partially reflective series of surfaces for the headphone drivers (now in front of each pinna and perpendicular to them, as per speaker listening) to bounce sound off and into the ear canal. In other words, the direct injection principle was thrown out the window and now the drivers were 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, the weight has been one of the main complaints levelled at a later enclosed design, the Stax SR-4070. 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 periperies of the drivers. In other words, the drivers could have bass (the lack of which has been a criticism of the 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 considerations, so a compromise between weight of the headphones and bass extension was reached.
The sound of the Sigma always has reduced very low bass because of some residual front to back driver cancellation through the mineral wool lining, but beyond that point, the earspeaker sound is very hard to fault compared to what one is used to. Firstly, the sound doesn’t have the bright edge of any other Stax headphone and secondly the reproduction of vocals comes as close to free of sibilant emphasis as possible. Both are what you hear in live, unamplified music – in particular piano and voice. In my opinion, the later substitution of the 580V high bias Lambda 404 headphone driver to replace the original driver, along with an upgrade of the original headphone cable, allows a reduction in high end frequency loss and an increase in very bottom end reproduction that shines a light on how successful Mr Hayashi’s earspeakers really are. The bass that is present until the very low bass roll-off, is of excellent quality. Certainly there are no bass instruments that just disappear as they descend the scale, as I heard with the Jecklin Float Electrostatics.
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.
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.
