OUR FULL REVIEW OF THE STAX SRS-3100 SYSTEM IS BELOW - IT WAS PART OF A HEADPHONE GROUP IN SOUND+IMAGE. YOU CAN READ THE FULL GROUP TEST AS PDFs BY CLICKING RIGHT >>>
Can there be a headphone brand more famous than Stax, and yet one that is more rarely experienced? I must shamefacedly admit that I’ve never before donned Stax headphones. [Our Editor chokes into his coffee at this revelation.]
So now’s my chance. Their fame, of course, in part rests on their electrostatic designs. And electrostatic designs do come with certain idiosyncrasies.
First, they cannot be driven by conventional headphone amplifiers. Rather than dynamic drivers (which use a coil and cone, somewhat like miniature loudspeakers) or planar magnetic drivers (which are a variation on the same theme), electrostatic drivers don’t use magnets at all. They rely on the attraction and repulsion of objects carrying electrical charges. As with magnets, opposites attract, while likes repulse.
So the driver consists of a very thin membrane (called the diaphragm) suspended between two grids (called stators). The signal is turned into high voltage charges on the stators. A high voltage is applied to the diaphragm and it moves accordingly.
In these headphones (or ‘earspeakers’, as it is Stax’s way to call them), the ‘bias’ voltage is 580 volts. This SRS-3100 system is designed for those new to Stax, so it includes both the SR-L300 ‘earspeakers’ and the SRM-252S ‘driver unit’.
Stax is a Japanese company. Founded in 1938, it produced its first electrostatic headphones way back in 1960. The manuals for the two devices are bilingual —Japanese and English. The latter evoked a sense of nostalgia in me, the slightly awkward wording (‘How to use a driver unit rightly’) bringing to mind some of the Japanese manuals of the 1970s.
Normal headphones are low (or lowish) impedance units, driven by low voltage, high current devices. The Stax earspeakers present an extremely high impedance to the driver unit: 145kohms says the manual. They are high voltage, low current devices. The driver unit acts as the conceptual equivalent of a headphone amplifier. It has two RCA inputs on the back for the two channels, plus a pass-through so that the signal can go on to other equipment. If you have a choice between connecting it to a headphone output or line output, you should generally choose the latter.
On the front of the driver unit is a level control and the headphone connection. Should you upgrade in the future — these headphones are pretty much the entry level into the Stax world — you can still use the driver. It is smallish, measuring 130mm wide and 40mm tall. The level control turns off the unit when rotated fully counter-clockwise. The whole thing is a solid-state analogue device.
The connection is a 5-pin affair (see above, the cable a flat ribbon type with six conductors, around 20mm across and nearly two metres long. The cable splits into two 38cm short of the headphones.
The headphone construction is strictly utilitarian, and seems to be primarily plastic. The back and sides of each cup are mostly grates — these headphones are clearly open backed. You can see the diaphragms through the grates. They’re large and oval, and measure 90mm by 45mm, a lot of surface to push air, because excursion is limited by the stators.
The headphones are very comfortable to wear. The rectangular cups give ample space for ears. And despite the plastic construction, there is no creaking or other mechanical noise from the hinges, and the only noise from the cable is if you drop it so that it tugs abruptly on the headphones.
The first thing to note is that with the driver unit, this headphone system is pretty much independent of gain in the source devices. Even European rules can’t get in the way! So there are no problems using it with a portable device, except of course that the driver unit is mains powered. So you can’t use these headphones portably (unless you invest in Stax’s recent portable driver).
The second is that their input impedance — that is, the input impedance of the driver unit — is quite high. I measured it at around 12.7kohms. Furthermore, the impedance seems to be even across the frequency spectrum. That means that you can use it with devices with high output impedances without worrying that the source will offer unbalanced levels at different frequencies.
I started with my classical selections with these headphones. It seemed more appropriate, somehow. The Schubert String Quintet, played by the Alan Berg Quartet with Heinrich Schiff on the extra cello, was a delight. It was so very sweet and smooth, yet the dynamic range seemed completely unrestrained.
There was plenty of dynamic range to encompass the Telarc 1812 Overture, ripped from CD. This has the closing cannon mixed in at a higher level than it was in the original ‘unplayable’ LPs, and given the hard 0dB limits of digital audio, the orchestral lead-up is recorded at a significantly lower level. So, on a lot of equipment the bulk of the music cannot be played at a satisfying level without risking damage upon the arrival of the climax. There were no such problems here. Again, the strings were sweet, and even in complex sections such as the appearance of the orchestral bells, all the elements of the sound were clear. When the cannon did arrive, they delivered their enormous crack, but not the feared crack of the diaphragm bottoming out against the stators. The near-infrasonic boom wasn’t quite as apparent as with some other headphones.
One unusual aspect of these headphones’ delivery of this music was earlier in the piece when the bass drum sounds. This usually stands out alone, above the music, thanks to Telarc’s practice of not limiting bass instruments (any instruments, really) in any way. Yet with these headphones the drum did not stand out and apart. Instead it seemed fully integrated into the sound. Was the bass perhaps a little less intense? Arguably, but the impact was at least as powerful as with any other equipment, and more than most.
The troublesome Melanie track came through as, well, a little troublesome. The transparency of these headphones ensured that the defects weren’t papered over. Nonetheless I found it enjoyable, because neither were the defects enhanced.
The Primus and Eminem were beautifully delivered, with the former even being disclosed with a generous helping of air (as was much of the classical material). The Eminem seemed to have the bass clear and strong, but down perhaps a couple of decibels from the norm. I’m not quite brave enough to suggest that the others were right and the Stax headphones were wrong. Regardless, it was entirely satisfying.