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Westone ADV Alpha ($249)

• 6.5mm drivers
• IPX3 water-resistant design
• includes 5 pairs silicone and 5 pairs foam tips
• 56-inch/1.4-meter cable with inline mike and iOS-compatible volume and iOS/Android-compatible play/pause/call button
• waterproof hardshell case included
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Westone ADV Alpha isolation

Isolation of the ADV Alpha, right channel, measured with pink noise at a reference level of 75 dB at 1 kHz. Numbers below 75 dB indicate a reduction in leakage of exterior sound into the headphones.
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Measurements
I measured the technical performance of the ADV Alpha using a G.R.A.S. RA0045 ear simulator, a Clio FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, and a Musical Fidelity V-Can headphone amplifier. Measurements were calibrated for coupler reference point, a point alent to slightly inside the ear canal, and slightly closer to the eardrum (and the measurement mike) than ear entrance point (EEP). I used one of Westone’s medium-sized silicone tips—the one that fit the coupler best—then inserted it, measured, reinserted it, measured again, and repeated the process until I was certain I was getting a good seal and the most characteristic result overall.

As happens sometimes with headphones, the frequency response measurements don’t square well with our subjective impressions. The response looks like it should be bassy and dull, with a broad bass boost centered at 65 Hz and only a slight treble emphasis peak at 5 kHz. (Normally we’d expect to see a larger peak, maybe +4 or +5 dB higher, and at a lower frequency around 3 kHz where it’d be more noticeable. Yet no one would describe the ADV Alpha as sounding bassy and dull. Channel matching is above-average, suggesting that the drivers are manufactured to tight tolerances. Thanks to the flat impedance, adding 70 ohms output impedance to the V-Can’s 5-ohm output impedance to simulate the effects of using a typical low-quality headphone amp has no effect at all on the ADV Alpha’s frequency response.
With the silicone tips installed, I measured outstanding isolation is excellent for a pair of over-ear headphones: dropping from a worst-case of -4 dB at 60 Hz (still very good for that frequency) to a minimum of -44 dB (the best I can recall measuring) at 4 kHz.

Except for a curious little peak at 1.5 kHz (possibly indicating a resonance of some sort),
total harmonic distortion (THD) at 100 dBA is very low, never rising to even 2%.
Impedance is dead flat at 20 ohms. Average sensitivity from 300 Hz to 6 kHz at the rated 21 ohms is 101.7 dB