I measured the Marshall Mode EQs using a G.R.A.S. Model 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), roughly the point at the center of your eardrum (in this case, the center of the measurement microphone). I used the medium-sized eartips because those best fit the RA0045. This is a “flat” measurement; no diffuse-field or freefield compensation curve was employed.
This is the frequency response of the Mode EQs in EQ1 mode. (The comparison with EQ2 mode is shown below.) This measurement may look very uneven, but it’s actually a fairly common response for earphones. The bass boost and the midrange peak at 2.5kHz are intended to compensate for the fact that the earphones effectively bypass the acoustical effects of the earlobes and ear canals.
This chart shows the Mode EQs’ frequency response in EQ1 and EQ2 modes. The response is effectively the same, except that EQ2 mode reduces bass by about 3dB.
Adding 70 ohms to the V-Can’s output impedance of 5 ohms, to simulate the effects of using a typical low-quality headphone amp, has a modest effect on the Mode EQs in EQ1 mode (shown here), but a much larger effect in EQ2. In EQ1, the higher-impedance source shows a bass boost of about 0.5dB and, beginning above 2.5kHz, a treble rolloff of about 2dB. In EQ2, though, using a low-quality amp (like the ones built into most Windows laptops and some cheap smartphones) will soften the sound significantly, boosting bass by about 2dB and, starting at about 1.5kHz, reducing the treble by a like amount.
You can see from this chart that the Mode EQs (shown here in EQ1 mode) have a more extreme bass boost and a more extreme upper-midrange/lower-treble peak than the NAD HP20s or the Sony XBA-H1s, both of which produce comparatively neutral sounds.
The Mode EQs’ spectral decay plot shows some unusual and very narrow resonances at 6, 8, and 12kHz, and a little more bass resonance than is usual for dynamic earphones, but there’s nothing particularly troubling here.
The total harmonic distortion (THD) of the Mode EQs in EQ1 mode is insignificant, showing a slight rise around 800Hz but never rising even to 2% at the very high listening level of 100dBA.
In this chart, the sound-pressure level (SPL) of external noise is 75dB; the numbers below that indicate attenuation of outside sounds. The Mode EQs’ isolation is perhaps a little better than average for earphones, with a reduction of 10 to 30dB through most of the audioband. Note that, depending on the size and shape of your ear canals and on the eartips you choose, your results may not be as good.
Here’s why the response in EQ2 mode changes a lot depending on the output impedance of the source device. The impedance swing in EQ2 is huge for earphones with dynamic drivers, dropping from 49 ohms in the bass to 17 ohms in the treble. It’s much less extreme in EQ1 mode, which has a maximum impedance of 31 ohms. I assume that the extreme impedance shift in EQ2 mode is due to the filter used in the EQ switch.
The Mode EQs’ sensitivity, measured between 300Hz and 3kHz with a 1mW signal calculated for the rated 30 ohms impedance, is 108.1dB in EQ1 mode, 107.0dB in EQ2 mode -- sensitive enough to get loud levels from practically any source device.
. . . Brent Butterworth
brentb@soundstagenetwork.com