Company Address: 940 Dominguez St., Carson, Cal. 90746, USA.
Let me start off with a mild paradox. The item under review is the Stax SR Lambda Professional Earspeaker system, which costs $800. I do not particularly like listening to headphones. Every experience I've had has reinforced my impression that a bad speaker provides a more musical listening experience than a good headphone. The paradox is that although the Lambda Pro is a headphone, I find it an excellent system for reproducing music.
The Stax Lambda Pro system is one of the few products unique enough to rise above the issue of its particular technology (of which it is an outstanding example) and be compared on a no-holds-barred basis with the best high-end components around. It also serves as a good introduction to the kind of musical reproduction that normally costs at least a thousand dollars more, and is uniquely suited to audiophiles who want to keep their high-end systems from dominating their homes or surplus incomes.
The key to this paradox is that the Lambda Pro "breaks the mold" in enough areas to emerge as a very special product. In order to appreciate its merits, however, it is necessary to understand my generic indictment against headphones. Most provide unnatural imaging with no center-fill, unrealistic and compressed dynamics, uncomfortable and erratic coupling to the ear, and a lack of depth, air and natural reverberation. Their frequency response is unusually irregular, lacking in bass and even the lower mid-bass. Dynamic phones exhibit a relatively significant loss of details, and electrostatics have a hard and often spitty treble.
Enter the Stax SR-Lambda Professional. This system consists of an advanced version of the Stax Lambda electrostatic earphones and a direct coupled (transformerless) Class-A amplifier unit called the SRM-1/MK2 Professional. The advances in the earphone include higher polarizing voltage, an exceptionally thin diaphragm, a wider electrode gap, and probably a great deal more besides. The key point is lower distortion and more dynamic range.
So much for the wonders of technology; it is human engineering and sound that count. To start with human engineering, the Stax Lambda Pro gets the basics right. The headphones are light, comfortable, and free from artificial restrictions on head movements. There are no problems because the cables are too heavy or stiff, or because the phones don't fit properly.
The open design allows prolonged and relatively fatigue-free listening. They cover the entire ear but don't seal you off from the sounds around you, and this helps minimize the "dead" or isolated character that earphones give to music.
The fact that the Stax Lambda Professionals are driven by a Class-A direct-drive amplifier means they don't interfere with the speaker-amplifier interface, a curse which often seriously degrades the sound of the loudspeaker. The system approach also makes the Lambda Pro unit flexible and portable. The drive unit has a volume control that adjusts for channel balance, and you can listen to anything with a high-level output without a preamp. That means you can easily set up an "armchair" system to listen to FM, tape, CD, or (with a preamp) even records. If you live in an apartment or have a family, you probably have severe constraints on when, where and how loud you can play music, and how well you can protect your high-end components from inexperienced or overenthusiastic hands.
This should have a powerful effect on any consideration of the Lambda Pros' cost-effectiveness. While they're truly expensive as earphones, they are cheap when viewed as the essential components of a second or personal high-end system. A comparable amplifier, preamp, and pair of high-end speakers would set you back at least $2,000-probably well over $3,000. I also use the word "comparable" advisedly. I did my listening to the Stax Lambda Pros during a period when I was comparing the Stax F81 Acoustat 1 + 1, and Quad ESL-63 electrostatic loudspeakers. The Stax Lambda Pros offered trade-offs that made them competitive with these very high-quality speaker systems and, in fact, with any dynamic system I have yet heard.
Let's begin with bass. The Lambda Pros don't eliminate the earphone curse. They can only match the better full-range loudspeakers down to about 100 or 200 Hz. While there's no precise way to measure the apparent loss in bass power, such a loss begins in the mid-bass and becomes more apparent in the deep bass. At the same time, the bass is extended, flat, and faster than most speakers. The feeling of bass "power" may be lacking, and bass dynamics a bit constricted, but the Lambda Pros do go way, way down into the deep bass and they're insensitive to room effects. Only the few audiophiles lucky enough to have extremely expensive speaker and amplifier systems, and rooms that allow them to perform their best, will get decisively better bass from their loudspeakers than you can get from the Stax Lambda Pros.
If you give these phones a chance, you'll also find that psychoacoustics are on their side. If bass is deep, flat and clean, the mind tends to correct for bass amplitude unless it is forcibly reminded of the contrast between a reduced and proper level. This is not true when the bass is merely excessive, particularly with the bass peaks and valleys common in most systems because of loudspeaker/room interactions. Flatness helped make the Lambda Pros' bass more listenable than that of many of the speakers I review, and enabled them to outperform the bass on the Stax F81 loudspeakers. It also made the Lambda Pros an ideal monitoring system when I wanted to check the timbre of bass on a record, or be sure I was not listening to room effects or speaker coloration in the bass. The Lambdas may not give you the most exciting sound from Telarc or Sheffield records, but they answer a lot of questions about exactly how the drum and bass viol on such records sound.
Moving on to the midrange, there still is some loss of the reverberation, air, and natural warmth common to live music and the best speakers. The loss, however, is less apparent than in any other earphones I have heard, including the regular Stax Lambda Pros driven by a switch box connected to a power amplifier. The midrange is also detailed, flat, and natural. The Lambda Pros will not surprise you with etched transients or some temporarily exciting variation in the music. They don't do anything unusual to the midrange. The Lambda Pros do not have the apparent rise in the upper midrange of the Stax F81 electrostatic speakers. They don't have the apparent roll-off of the Acoustats. They do sound "close in"--let's say Row C in the concert hall--but you can listen to the midrange for a long, long time without hearing the Lambda Pros caught out in terms of sound quality.
If you like the midrange of such speakers as the Quad ESL-63s, the Thiels, the Vandersteens, the Martin-Logans, the Fuseliers, etc., you will find the midrange of the Stax Lambda Pro to be a good overall match in clarity and timbre, and an interesting point of comparison. Further, the Lambda Pros' midrange again offers exceptional freedom from room effects. If they sound slightly dead in terms of depth and air, they also free the sound from the characteristics of the room you're in. If you prefer to hear the midrange of the concert hall or performance as recorded on the source material, you will hear it on the Lambda Pros.
I should also note that the SRM-1/MK2 drive system is one of the least problematic Class-A amplifiers I have heard. It is definitely a transistor unit, which tube lovers will recognize immediately, but it is clean and extended. It may not be a match for the latest Krell power amplifiers, but it rivals the high end transistor amplifiers I've heard in recent months, including the Thresholds. This became very apparent in comparing interconnects. The Lambda Pros merit the best Monster Cable Interlink Reference, Peterson, Livewire, Discrete Audio, or Straightwire interconnects. They also-as Bert Whyte pointed out in the November 1983 issue of Audio-reveal every detail of the source material and equipment used to drive the SRM-1/MK2.
The highs are extended, clean, and very musical. My Koss electrostatic earphones tend to burn every bit of hiss and upper-midrange and upper octave hardness right into the ear. The Stax Lambda Pros minimize both the excess treble in most electrostatic phones, and the dullness and grain of dynamic and electret earphones.
The specifications for the Lambda Pros show a rise from about 4.5 kHz to beyond audibility. But listening to a wide range of music reveals a steady-though slight-roll-off beginning somewhere around 3.5 kHz. Given the proximity of the driver to the ear, this ends in making the upper octaves of the Lambda Pros sound relatively flat up to about 17 kHz. My guess is they're not flat much beyond this frequency, and start to exhibit a sharp roll-off, but the meters on my golden ears aren't accurate enough in this part of the top octave for me to know. In any case, the Lambda Pros have enough response far beyond 17 kHz to provide the nearly subliminal consciousness of extended highs that is only present in the best super-tweeters, or in a few ribbon and specially designed electrostatic speakers.
There is an old joke about an audiophile who walked into a concert hall to hear live music for the first time and wondered where all the highs and sharply etched imaging went. He will have the same experience if he wanders into the Lambda Pros. Like the midrange, the highs are best characterized by those old audio chestnuts, "sonically neutral" and "musically natural." That may not be "exciting" if you love sound, but it is very exciting if you love music.
As for imaging and depth, the Lambdas do not rival loudspeakers. They have more center-fill and spread than most earphones. They can sound exciting and reasonably natural with the few binaural tapes that are available, but they never "float" an image in a perfectly natural way. They do have depth if the recording has depth (try some of the Reference Recording, Opus, Wilson Audio, Lyrita, and Proprius records), but not enough source material has the natural depth to compensate for the depth that most listening rooms add to loudspeakers' sound.
The Stax Lambda Pros do reproduce the entire dynamic range. They easily outperform Quad ESL-63s in this regard, and rival even most big dynamic loudspeakers. They reproduce soft passages nearly as well as the Quad ESL-63s and Fuselier 3.3s, which are both outstanding in this respect. They do not, however, have the feeling of power or "air" that is natural in live music or in the very best loudspeakers operating in a room. Nonetheless, the Stax Lambda Pros have a different kind of sound from speakers.
If you listen long enough to get used to the changes, you'll notice that at no point does the room begin to interact with the sound and color it. You win a few points and lose a few points.
To put it personally, I used to have a pair of LS-3/5As in my equipment room and a pair of small Spendor speakers on my test bench. They were awkwardly located on shelves in the wrong area, and I finally tired of trying to use them to fine-tune equipment, compare given components, or (as a desperate last resort) listen to music. The Stax Lambda Professional Earspeaker system does all of these jobs quite well. It moves easily between equipment room and test bench. Most importantly, the SR-Lambda Pros allow me the vice of Vivaldi after my wife imposes her official sonic curfew. The system is cheaper than any single combination of a small monitor speaker and amplifier that I've used previously-and it's more musically satisfying.
-Anthony H. Cordesman
(adapted from Audio Jan. 1985)
Also see:
Stax SR-Omega Earspeakers And SRM-T1S Drive Amp (Feb. 1995)