Stax Lambda Pro

The Stax Lambda Pro was the very first Pro Bias (580V) headphone (or “earspeaker”) the Japanese manufacturer produced. It was mostly targeted for studios and professional use.

Don’t be afraid by the rectangular look of the Lambda ; it’s quite comfortable with light clamping and no headband pressure. Build is very cheap. Headband yokes feel they could break easily, but they are made of very solid plastic

My pair developped a channel imbalance after a few months of use – the left driver would be silent at start-up and required 3-5 minutes of voltage supply to charge the stators and reach full volume. Very weird at first, but I got used to it. It definitely affected resale value.

○ Release : 1982
○ Current status : Discontinued
○ Type : Over-ear / Open-back
○ Measured weight : 325g
○ Impedance : 129k Ohms
○ Sensitivity : 101dB/100V
○ Average used price : $250-350

Sound Impression
Balanced presentation, though a bit on a lean / bright curve. Bass is really impressive ; doing some sine sweep and I can easily hear rumble down to 21-22hz. The Lambda Pro has old style vinyl earpads, they have some thickness on the rear side and getting a good seal is the key to have perfect bass extension, otherwise you’ll get a boomy one-note midbass bump and nothing below 60hz. Bass is tight and clean but lacks slam of dynamics and planars.

Midrange has good response, but is a bit recessed and lacking some 2-3 khz upper-mids body, relatively to the treble. Highs are quite detailed and strong, especially around 7-10hz. Think ‘sss’, this sound is emphasized a bit too much for my liking. Edginess / harshness area (4-7khz, ‘shh’ sounds) is better behaved on this headphone.

The Λ-Pro has absolutely exceptional upper-treble extension and amount of air. This headphone is horrible to use for badly recorded music with lot of parasites and various buzzing noises in the upper registers. It sounds a bit too quick to me. This, combined with the lean tonality, makes this Lambda often sound a bit too unnatural, lacking realistic tone and body.

Staging is quite wide, but a bit too 2D ; I would have appreciated better sense of depth. But clarity is top notch ; this is by far the most open and airy headphone I have heard under $500. Absolutely no other headphone can come close to this one, not even more recent budget Lambdas (SR303, SR407) I had the occasion to hear briefly.

I have always been impressed by the Lambda Pro, considering it’s close to 40 years. I would recommend pairing it with tube amps, like the SRM-T1 or 006T in order to add some warmth. For music listening, in the electrostatic category, I prefer the Koss ESP950 : much more natural and smoother tonality, although lacking in sub-bass and detail compared to the Lambda.

Measurements & Resources