Note: The rating and pros/cons above are for the normal-bias SR-Lambda. This review also makes mention of the Lambda Pro, which I also have in my possession.
Stax has always been a vaunted and controversial name in high-end audio. Their fans claim that no dynamic headphone can so much as touch the heights reached by the cheapest electrostat; their detractors malign their plasticky build, and plasticky, unrealistic sound. (As always, the truth lies somewhere in between.) But I was intrigued enough that when I had a free moment at CanJam NYC this year, I made a beeline to the Stax room to try out a couple of Staxen. I had always thought of buying some Lambda or other, you see. And after trying the L700 (and later on reviewing it - you can find that review on MajorHifi) I was moved to buy my own budget(-ish) Stax setup, an SRM-1/MK-2 and an SR-Lambda Pro that I ordered off Yahoo Auctions.
And the Lambda Pro came, and I liked it...but not that much. I was surprised by what I perceived as a sort of V-shaped sound signature, with a really quite recessed midrange and a really sharp, annoying treble peak at around 10kHz. The resolution was there, yes, but the tonality lagged far beyond what I had experienced with the L700. After digging around online, I discovered that, yes, the Lambda Pro tends to have a reputation for having a recessed midrange, and the original Lambda might be more my speed. So, intending to sell the Lambda Pro as fast as possible, I picked up a Lambda from another user on Head-Fi.
Yes, this is closer to what I was going for. I haven't yet had a chance to compare these to the L700, but I expect I'll find them to be more similar than not, because a lot of what I'm getting from the Lambda matches what I remember getting from the L700. But that's another comparison for another time.
The SR-Lambda is not totally linear. There are some emphases especially in the mids that can throw things out of whack from time to time - more in some recordings than others, though. Generally I do find that these sound "right," especially compared with the decidedly wrong-sounding Lambda Pro. They're great for classical, not really as plasticky-sounding as I've been led to believe, and have a great and agreeable tonality. Basically, the SR-Lambda sounds like a lambda, but a very good and competent one.
Bassheads need not apply. The bass is linear (do NOT believe any measurements of Lambdas before the current generation with rolled-off bass - the bass is rolled-off in the new ones, but not the old ones, and measurements that say otherwise were taken without a good seal), going audibly down to 20Hz, though it may be slightly reduced in level by the time it gets there. It has some impact and power, but the Lambda Pro does notably better here. But it's going to be a hell of a lot better than a stock L700, that's for sure. I'd say it's a bit better than, say, the Sundara as well. It's not "subby," though, so trve bassheads will hate these. I do have some trouble really discerning what's going on in the subbass with, say, Burial, but it takes bass EQ like a champ.
The midrange has that characteristic Lambda shout somewhere between 1kHz and 2kHz. This throws the tonality of instruments slightly off (but very slightly; I don't perceive these as very unrealistic at all). More importantly, the Lambda can play vocals kind of weirdly, emphasizing "ah" sounds more than it should. For a good example, listen to "Quitting Time" by the Roches - the "AH" part of "QUITTING TAAAHHHHIIIME" right in the beginning is certainly overpronounced and a little grating with these headphones. Looking at CSDs, there is a very small amount of ringing in this region in other Lambdas - I can't find a CSD of the normal-bias Lambdas, but I suspect its driver, too, is very slightly ill-behaved in this region.
Above that little emphasis, the mids are kind of laid-back all the way up to 4kHz. So the overall tone of the midrange is pretty agreeable, with that 1-2kHz bump lending a bit of an unnatural coloration especially to vocals. Piano can also be an issue, as well as flute, or any issue that plays notes in the 1-2kHz range - these notes will come across as hard. The emphasis is something like 3-4dB - not terrible, but not slight enough to go unnoticed. Very "sweet" midrange, whatever that means - kind of like a soft yawn.
There is an emphasis on the upper treble starting at around 8kHz and continuing up indefinitely (there is no roll-off); this is accompanied by somewhat of a hole from 6-8kHz. But while the treble in the Lambda Pro was near unbearable without EQ, it's fine with the normal-bias Lambdas. You sure get a lot of detail with these things, but with recordings that already have an emphasis on air it can be overwhelming, and cymbals as realistic as they could be, since they have a lot more "air" than they do "body." There might be a little smearing going on, but that could just as easily be my DAC (the Bifrost MB; I need to upgrade).
Soundstage is good. Pretty wide, airy (I keep coming back to that word, don't I?), with good instrument placement and imaging, though maybe not quite as wide as the Lambda Pro with its recessed midrange. The high resolution helps with staging, of course, because you get more of the reverberations of the recording space, giving you more clues to help localize instruments. Imaging is perhaps not the most precise ever. Some have accused these of having a "flat" stage, but I wouldn't entirely agree - I think the stage dimensions are fine and natural, personally. These are notably better at doing intimate recordings justice than the Lambda Pro or even the SR-009s.
OK, let's talk a bit about the Lambda Pro and some of the issues I had with it. My rating of that would be closer to 3 stars, and that's mostly because of unbearable colorations in the stock sound. For a while I tolerated it by using the EQ settings from the Stax ED-1, but to be honest, that didn't sound very good either - there's a 3kHz bump with that of about 6.5dB, which helps make up for the Lambda Pro's recessed mids, but it's too much. More importantly, the headphones didn't really sound fun with the ED-1 on. Tonal accuracy was broadly there, but there was nothing arresting about what was going on. Even more unfortunately, the Lambda Pros demonstrated that they were a bit less willing to take EQ than I would imagine. With EQ, the Lambda shout was still there, just subdued, but it would rear its ugly head every once in a while; and that 6.5dB upper midrange peak would get quite harsh from time to time. Treble retained a bit of its spiciness, too.
Build: The Lambda and Lambda Pro are both the cheaply-built monstrosities we associate with Stax, but since it was the 80s, I think it's forgivable. Frankly, I think the modern Lambda designs are forgivable, too. I like the boxy look, but I recognize that position puts me in the minority.
Anyway, more importantly, these are old, so you're going to get an old product when you buy one. On mine, the earpads have hardened considerably (though not so much on my Pro as on my normal-bias Lambdas). They're still very comfortable, though, as the clamping force is very light and the headphones themselves are pretty light too. There's also a list of "rules for use," so to speak, so that you don't damage the drivers. Don't push them into your head, don't play music without the headphones on, don't listen to them with wet hair (this one might be a myth, frankly), etc. When I was showing them to a friend of mine, I relayed this list of rules, and he said with very genuine confusion: "why do you own these?" It's a good question, and one that I consider every day. But if you want great sound, and you're not paying for that sound in money (because these are very cheap for what they offer), you're gonna pay for it with the fact that you own a piece of arcane technology that's very easy to destroy if you mishandle it. Channel imbalance is apparently common, although not a problem on my pair.
Value: For the "dynamic is best" faction, the HD600 may well still be a better value proposition than the Lambda. Obviously the 600 has less resolving power than the Lambda, but some will consider the timbre better and more natural (not me, although perhaps I should wait till I can A/B the two). But considering that the Lambda pretty much performs up to the standards of today's $1,500 L700 and can be had for $300 or under if you're lucky, I'd say it's pretty damn good. 10/10 value; you will not get better for the price except through a difference in taste or a stroke of luck (I feel like the ATH-AD2000, which I got for $200, is on the level of these, for example, but not in terms of absolute performance).
Conclusion: If you're planning to use the SR-Lambdas as all-rounders, let me just stop you there. They in no way give you an accurate picture of what your recording sounds like without heavy EQ - too heavy to be worth it, in my opinion. Instead, these are headphones that you get for the experience, for the "electrostat sound," to enjoy your recordings in a new way. And for that, they work wonderfully. Yes, the treble is hashy, and the midrange is uneven in the typical Lambda-ish way. The midrange unevenness can occasionally be grating and harsh, especially with operatic vocals. That said, they're definitely a cool thing that I'm happy to own.
1 star deducted for the Lambda shout & thinned-out treble. As for the rest, it depends on your taste. For $300, I'd say they're very, very good, but something like the HD600 or maybe the HE-500 or something would be a safer choice.