Stax SR-Lambda Pro Classic headphones
Audiophiles discovered the benefits of headphone listening years ago. I still remember my first set of Koss Stereophonesnirvana for a college student in a tiny, shared dorm room. This ability to listen privately without disturbingor being disturbed byothers remains the major reason audiophiles seek out good headphones.
Certainly there are negatives to be overcome. Comfort is a concernthe most comfortable headphones are no headphones. And headphone sound is a mixed bagequivalently priced loudspeakers will generally not play at quite as high a level with reasonably low distortion, and because they need to move enough air to fill a room with sound, they have to work harder (and thus seldom sound as effortless as good headphones). But loudspeakers do move air, and the "feel" of a soundfield generated by loudspeakersespecially, with capable loudspeakers, in the bass endis something which headphones simply cannot duplicate. Furthermore, the soundstage reproduced by headphones is never quite right, because most recordings are produced to play back correctly through loudspeakers (footnote 1).
While headphone listening remains secondary to that of loudspeakers for most serious listeners, it's still an important alternative for many. And while good conventional headphones exist, electrostatics are usually considered first when the highest playback quality is required. As always, there are exceptions (Grado's headphones come immediately to mind), but most high-end headphones are electrostaticsuch designs offer the benefits of electrostatic loudspeakers without their dynamic limitations. Last year I reviewed the Koss ESP/950 electrostatics (Vol.15 No.12), a remarkable set of headphones from the company that practically invented headphones for serious home listening. Here I listen to examples from two other companies, each known for its headphones since Pluto was a pup.
If you're familiar with any of Stax's previous Lambda headphones, you'll immediately recognize the Pro Classicits construction is identical to the others, including the top-of-the-line SR-Lambda Signature, except that it's black instead of chocolate brown, and has a slightly stiffer headband. Its 1.5µ'mthick diaphragm, however, is slightly less sophisticated than the Signatures' 1µ'mthick diaphragm. Both were equally comfortable, though for reasons I can't explain, the less expensive 'phones caused minor itching of my external ears. This probably won't bother everyone, but I do recommend that anyone in the market for headphones wear the final candidates for at least an hour (listening goes without saying, of course!) to ensure that they're comfortablea few minutes isn't always long enough. Some audiophiles have also complained that the vinyl pads on the Lambda 'phones don't "breathe" well, becoming uncomfortably sweaty over time. I was never bothered by this, but you should check it out for yourself.
The SRM-Xh direct-drive amp (Stax calls it the Driver Unit) is the smallest, simplest such unit furnished with any of the Lambda 'phones. In fact, it seems that the price difference between the Pro Classic and the next-model-up SR-Lambda Pro 3 is accounted for in its larger, more complex SRM-1/Mk.II Driver Unit. The simpler SRM-Xh has a single set of inputs, one headphone output, an On/Off switch, a single volume control, and is powered by one of Stax's ubiquitous plug-in transformers. (Neither the Stax nor the Sennheiser has a balance adjuster, and I never missed it.) The only functional problem I had with the SRM-Xh was that it's so lightweight that some of the stiffer audiophile cables (eg, TARA Labs) tended to lift it into a pre-launch position. (At lasta new use for one of those Magic Bricks.)
The Pro Classic operates with the same 580V DC bias that drives all the more expensive Lambda 'phones, so it can be used with any of Stax's larger Driver Units. For owners of, say, the SRM-T1 tube amplifier which comes with the Lambda Signature (and which has three outputs, two of which will drive any Lambda-series 'phones), the Pro Classics can be purchased without the SRM-Xh for $474.95if you want an extra set of compatible 'phones but don't want to spring for another Signature. The Pro Classic's sensitivity matches the Signature's; both listeners will listen at the same playback level.
You won't be surprised to know that the Pro Classic definitely has the Lambda family sound. If you're not familiar with the Stax Lambdas, one listen'll tell you all you really need to know: There are only a handful of headphones that can compete sonically with the SR-Lambda Pro Classic, and most of them are other Lambda models.
The Pro Classic will tell you, to an uncanny degree, just what's on the program material you're listening to. As with all headphones I've listened to, that won't include an accurate representation of the soundstagethe in-the-head sensation endemic to headphone listening substantially remains. This problem has been addressed on occasion by special circuitsStax still markets their $900 ED-1 diffuse-field equalizer (reviewed in Vol.12 No.4 & Vol.14 No.5), designed to compensate for the fact that listening through headphones is very different from listening through loudspeakers. As far as I'm concerned, none of these devices has cured the problem, though some are worthwhile and often display considerable ingenuity. (See JA's review of the HeadRoom headphone amplifier in last month's issue.)
Only rarely did I get the sensation that something was happening in front of me with the Pro Classic. More often than not, the soundstage stretched from just beyond my left ear, through my head, to just beyond my right ear. Still, all the Stax Lambdas, perhaps because they have a rather laid-back sound to begin with, are well above average in their ability to reduce the claustrophobia of headphone listening, even if they don't get the sound out in front, where most of it belongs. But this is so common with headphones that it shouldn't be taken as a specific criticism of the Pro Classic.
Within this limitation, however, the Pro Classic's imaging was precisely focuseda strength of headphones. The headphone designer knows the listening environment and has control of the listener's location (or their ears) within that environment. Given a good spectral balance between the left and right earpieces (hardly a given for all headphones), the image should be well definedand, with the Pro Classic, it is. Depth was reasonable, though again, the inherent perspective of headphone listening prevented it from being as convincing as with good, properly set-up loudspeakers.
Footnote 1: Binaural recordings, often made with a dummy head that has microphones where the ears should be, are the rare exception, and only sound the way they were intended through earphones. They can provide a startling sense of spectral realism, but in my experience still don't get the frontal image completely out where it belongs.