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Friday, August 23, 2013

STAX SR-003 MK1: Electrostatic in the Ear

Disclaimer: This loan has been provided by my friend, vAsurada. This particular pair is SR-003 mkI, not mkII. Measurement has been carried out at 6 mm away from the reference plane with its headband removed.

Released as a Pro-bias version of SR-001 mkII in 1997, STAX SR-003 features small form factor compared to other full-sized headphone from the manufacturer for portable usage, and a 1.5 μm diaphragm, which is the same thickness as the diaphragm of current Lambda models.

And the question is, can this IEM perform as good?

PRO: There are quite a few: Very quick transient characteristic, warm-bass, wide bandwidth, low distortion, and linear frequency response with a downward-slope of about -2 dB/oct.

CON: Fitting is quite tricky, due to the IEM's large housing.

ON SECOND THOUGHT #1: Although SR-003's optimum insertion depth is about 6 mm away from the reference plane, due to its uber-low acoustic output impedance, any insertion depth yields more or less the same linearity along the frequency spectrum.

ON SECOND THOUGHT #2: Modifying SR-003's acoustic damping scheme radically re-shapes the frequency response. While a foam piece inserted in the nozzle suppresses peaks in the mid-range, blocking the rear vent interferes damping of the driver by a great degree.

ON SECOND THOUGHT #3: Surprisingly, the rear duct of SR-003's headband is a part of the IEM's acoustic damping system. By adjusting the volume of air behind the driver, the headband duct cuts off 4.5 kHz while boosting 6 kHz. Consequently, the frequency response becomes similar to that of SR-Lambda series.

ON SECOND THOUGHT #4: Again, SR-003 is virtually free of insertion-depth related issue. Period.

ON SECOND THOUGHT #5: Modifying the rear cup portion only affect the mid-range damping characteristic.

ON SECOND THOUGHT #6: As previously analyzed, ED-1 equalizer, which is made as SR-Lambda Professional's proprietary diffuse-field synthesizer, effectively turns Basic and Signature into Hi-Fidelity headphones. And when ED-1 is coupled with SR-003, the IEM becomes even more linear than it already is.

ON SECOND THOUGHT #7: Whether the IEM is coupled with ED-1 or not, the sound quality is still of top-notch. As its electroacoustic performance characteristic is so great, STAX SR-003 becomes the very first headphone that goes on my favorite list.


  1. thank you very much for nice review!

  2. Rin,
    Your favorites list?
    I will now consider t In Ear Speaker!!!
    Thanks, Jim

  3. Is Etymotic ER4 still on top of the list??

    1. When choosing my first and last IEM i was considering er4 and sr003. I ve never heard either. I chose er4. All these years i thought i chose right. It is funny to find out i was wrong.

    2. Haha, don't worry Vitaly. ER4 is still a solid contender with great sound quality. I'd still choose ER-4B for binaural simulation.

      However, it is not on my fav list for three reasons:

      1. ER4 is not flat in the sub-bass range; IMHO lacking is worse than bloated.
      2. High frequency extension is too short.
      3. And most importantly, ER4 is extremely prone to complications derived from insertion-depth & bore-resonance.


    3. I did have a long fight with Er4 against its sibilance as I just could not put it deep enough. Then someone (kudos to you!) on this blog suggested getting shure olives and they did improve things a lot. But yes, now HF extension seems too short which took away a bit of sparkle from ER.
      On the other hand a whole bunch of people did criticise SR003 for being too boomy (i think) and that it sounds boring. were they just deaf or plain wrong...

    4. A good seal is vital for SR-003. If the IEM is not sealed well, polarization resonance(which rings of course) appears somewhere in the low frequency range, and its frequency varies depending on how much of leak is introduced.