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Thursday, August 15, 2013

Westone UM3X

Disclaimer: This IEM was sent all the way from Singapore. Much appreciated, Nate! Measurement h as been carried out at the reference plane with a pair of small Westone mushroom tips. Unfortunately, it turned out his pair is faulty on the left.. :-/ Thus, only the electroacoustic performance of the right unit will be discussed in this analysis. 

I first auditioned this IEM at the CanJam 09, which was held in Los Angeles, California, along with Westone 3. As far as I can recall, my initial impression was just "OK" and UM3X was slightly more linear than Westone 3, at least to my ears.

And four years later, one of the regular visitors of my blog, Nate, sent in his pair for analysis with specific requests. And as always, I never turn down a friend's request ;)

PRO: The problematic 10 kHz can easily be knocked off by adjusting the insertion depth. UM3X's mid-range is recessed due to its electrically linear frequency response characteristic.

CON: Not only the polarity of the IEM is inverted, there's a funky pre-ringing present in the time domain (a cosine burst?). Although it should be inaudible due to the effect of temporal masking, such electroacoustic behavior has never been measured previously.

ON SECOND THOUGHT #1: Unless the IEM is inserted very deep beyond the reference plane, or very shallow, about 6mm away from the reference plane, the peak 10 kHz will always be present, causing an audible artifact in the treble.

ON SECOND THOUGHT #2: Adding a serial resistance to the IEM only boosts the mid-range.

ON SECOND THOUGHT #3: The stock damper of UM3X is 680 Ω (white), which is glued to the nozzle. However, users may add a damper on top of the stock one. As seen above, additional acoustic resistance attenuates the mid-range and treble.

ON SECOND THOUGHT #4: And here's the result of Nate's special request. (Click on the image for an additional detail) As expected, the shallower the insertion depth gets, the more linear the treble becomes.

ON SECOND THOUGHT #5: And here's my recommendation for UM3X users: Equip a 33Ω resistance adapter, a pair of Shure Olive(PA910) sleeves, and insert the IEM as deep as possible. Or you may insert it very shallow if the size of Olive is large enough to achieve the same level of linearity in the treble. The resulting tonality still lacks treble, but somewhat resembles that of Audeze LCD-2, believe it or not.

ON SECOND THOUGHT #6: The frequency response of Westone UM3X is very far from the reference curve suggested by Dr. Sean Olive of Harman, as much as 10 dB in the treble.


  1. What's with that FR and Z matching? The mismatch gets to roughly 5db in the mid region and the sub bass is even worse.

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  3. Mr. Choi:

    I have 2 pairs of UM3X and I intend to take one pair apart to put those drivers in a custom mold IEM.
    Is that a good idea if I don't put any dampers in the canal tubes?
    Or would you recommend a damper which doesn't tame the high/high mids so much like the 680Ohm does?
    thanks in advance!