I measured the KEF M200 earphones using a G.R.A.S. RA0045 ear simulator, a Clio 10 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 drum reference point (DRP), the equivalent of a earphone’s response at the surface of your eardrum. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed. I used the medium-size silicone tips that I received with the review samples. Because of the large diameter of the M200s’ sound tubes, I had to press lightly with a fingertip to get a good seal in the ear simulator.
There’s some disagreement about what constitutes a good frequency-response measurement for earphones, but I think all experts would agree that this one looks unusual. That dip in the midrange centered at about 900Hz is fairly common, but here it’s about -6dB lower than I usually measure. The treble response above 4kHz is cleaner than I’m used to seeing, with just one strong, narrow peak at 8kHz instead of the usual multiple, spread-out peaks.
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 does affect the M200s’ performance, but only in a band of about one-third of an octave centered at 13kHz, where the response drops about -4dB with the high-impedance source. This would be audible to most people, although whether you’d perceive it as an improvement in or a degradation of the sound would depend on your hearing and taste.
This comparison of the M200s with NAD’s Viso HP20 and Bowers & Wilkins’ C5 earphones suggests that the KEFs are the least likely to be perceived as having a flat response, thanks to that big midrange dip. To my ears (and those of many other reviewers), the Viso HP20s sound fairly flat, the C5s a little on the bassy side.
The spectral-decay (waterfall) plot looks clean except for one very strong resonance at 4.8kHz. But given the narrowness of this resonance, I expect it would be audible only with certain pieces of music, and then only fleetingly.
The total harmonic distortion (THD) at 100dBA is a little high relative to the best earphones I’ve measured, hitting about 3% at 1kHz, but given that 3% isn’t such a high distortion level in transducers, and that 100dBA is an extremely loud playback level, I doubt you’d encounter this flaw in normal listening.
In this chart, the external noise level is 75dB SPL; numbers below that indicate the degree of attenuation of outside sounds. Thanks probably to its big, fat 6.8mm sound tubes, the M200s deliver good isolation from outside sounds. In the key band between 100Hz and 1kHz, the reduction ranges from -11dB at 100Hz to -27dB at 1kHz, and even better at higher frequencies.
The impedance magnitude is almost dead flat (if unusually low) at 12.5 ohms; the impedance phase is also almost entirely flat.
The M200s’ average sensitivity from 300Hz to 3kHz at the rated 12 ohms measures 96.7dB, which is -7 to -10dB lower than I measure with typical earphones. That’s because of the big midrange dip. With the M200s, you’ll probably need to turn your smartphone up to nearly maximum volume.
. . . Brent Butterworth
brentb@soundstagenetwork.com
