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Monday, July 1, 2013

Stax SR-lambda Signature: A legend revised

Disclaimer: This analysis was made possible by the support of my friend, vAsurada. 
Measurement has been carried out with acoustic leak minimized, by using a silicone putty as a sealant.

Released in 1987, Stax SR-Λ(Lambda) Signature is a direct successor of SR-Lambda Professional. While everything remains the same from Professional, the diaphragm is now only a micron thick, yielding even greater frequency response extension than its predecessors.

PRO: A well-extended flat frequency response & clean transient characteristic. The pair is extremely well-matched. Not much of a step up from SR-Lambda Professional, but the performance is great nonetheless.

CON: A good acoustic seal is vital for sound reproduction below 100 Hz. It is such a shame that the cable is not replaceable.

ON SECOND THOUGHT #1: The difference between the predecessor, Professional, and Signature is rather small, but is definitely present. The rear volume has been damped slightly with foam to decrease the air compliance in order to bring up the mid-range.

ON SECOND THOUGHT #2: Stax SR-Lambda Professional can be paired with its proprietary equalizer unit, ED-1, to simulate an accurate diffuse-field sound. Moreover, ED-1 can be used in conjunction with SR-Lambda Signature as well. The simulated result is a somewhat downward-tilted diffuse-field characteristic, which is more suitable for general music listening, as some listeners find the true diffuse-field target to be overly bright and harsh.

ON SECOND THOUGHT #3: A free-field analysis has been carried out at various locations within the frontal volume of the housing using an accurately calibrated microphone. The test result suggests that the entire surface of SR-Lambda Signature's diaphragm is not behaving as uniform as originally expected, but definitely more symmetrical than that of SR-Lambda Professional.

ON SECOND THOUGHT #4: By default, this headphone is far from the Olive-Welti target, meaning that the tonality is simply too harsh to be considered as hi-fidelity.  A substantial amount of equalization is needed here just like the predecessor, SR-Lambda Professional.

ON SECOND THOUGHT #5: Just for curiosity, EURI's SR-lambda Signature data has been overlayed on top of the manufacturer calibration plot obtained with B&K 4153, which is a 6cc coupler, for a peer-review. Considering the fact that the former data is of DRP and the latter is of ERP, it can be assumed these plots correspond very well to each other.


  1. I am very surprised at fine channel matching despite it is appx. 25 years old! Thank you for review of my Lambda :) lol

  2. I must thank you for measuring the signature. Measurements are near impossible to come by! They are a really nice set of 'phones.. How do you like them?

    1. You're welcome! The credit goes to my friend, vAsurada, who generously let me borrow his pair of Signature.

  3. Just got the pair in good condition! What a sound! I have my own collection of over 60 native DSD128 live jazz and classical albums... After the picture I had with Sennheiser HD 600 for a long time I just can not stop listening the tracks from the collection... Now I need a better DAC (I am playing the tracks directly from the Korg MR-1000 recorder). If PS Audio - even Junior - will get into my hands, all I need to experience phenomenal sound is a NAS with a tablet to control replay tracks on it and a DAC that accepts LAN input. Or a few JitterBug units if all the staff is in one place and a short USB cables will do. I am quite sure that LAN connectivity is a way forward and I will be hunting for a suitably equipped DAC to get it all right! Regards. S. Native DSD128 anyone? The entire collection will be available with the NAS at the most attractive combined price.