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