I measured the Marshall Mid A.N.C.s using a G.R.A.S. Model 43AG ear/cheek simulator/RA0402 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 amp. On the Model 43AG, I used the original G.R.A.S. KB0065 simulated pinna for most measurements, as well as the new KB5000 pinna for certain measurements, as noted. For tests in Bluetooth mode, I used a Sony HWS-BTA2W Bluetooth transmitter to send signals from the Clio 10 FW to the headphones. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
The Mid A.N.C.s’ frequency response (shown here with NC on, and a wired connection) looks fairly standard, except that the 3kHz peak found in most headphones is unusually strong. In my experience, that extra couple dB is likely to make headphones sound just a bit on the bright side.
This chart shows the right-channel frequency response of the Mid A.N.C.s measured in some of its various operating modes: wired passive (NC off), wired (NC on), and wired Bluetooth (NC on). They’re pretty close to each other, which is a good thing -- the Mid A.N.C.s should sound pretty similar no matter what mode you’re in. The Bluetooth mode looks as if it might sound a bit softer, but the gating required for the Clio analyzer to compensate for Bluetooth’s latency might be contributing to that effect in the measurement.
This chart shows the Mid A.N.C.s’ measured right-channel frequency response in wired mode with NC on, measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna (which I’ll eventually switch to because it more accurately reflects the structure and pliability of the human ear). I include this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review until I completely switch to the new pinna.
This chart shows the Mid A.N.C.s’ measured right-channel frequency response compared with three other noise-canceling headphones: the PSB M4U 8s, the Sony WH-1000X Mk.2s, and the Bose QC25s. Clearly, the Mid A.N.C.s have a little more energy between about 600Hz and 3.5kHz, with no extra bass to balance it out, so they’re likely to sound just a bit bright.
This spectral-decay (waterfall) chart shows the results in wired mode; the latency introduced by Bluetooth prevented me from getting a reliable measurement in that mode. While the resonance in the bass is unusually low, there’s a somewhat strong resonance centered at about 4kHz that doesn’t seem to correspond with the frequency-response measurements. Will this cause a slight brightness? Possibly.
Bluetooth’s latency meant that I had to measure the total harmonic distortion (THD) of the Mid A.N.C.s in wired mode. Distortion is a little higher than the norm, though the problem seems restricted to the bass; remember, most music has very little content below 40Hz.
In this chart, the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. The isolation of the Mid A.N.C.s is just about the same as that of another on-ear NC model I recently measured, the AKG N60 NC Wireless. Not surprisingly, neither can touch the over-ear Bose QC35 IIs, but they provide enough NC to make a plane ride much more pleasant.
The Mid A.N.C.s’ impedance magnitude in wired mode is dead flat at 38 ohms, with a nearly flat phase response. In active mode with NC on, it’s dead flat at 880 ohms, with flat phase response.
The sensitivity of the Mid A.N.C.s, measured between 300Hz and 3kHz with a 1mW signal calculated for the specified 32 ohms impedance, is 98.0dB in wired passive mode, and 102.2dB in wired active mode with NC on. They won’t deliver enough volume to blast out your eardrums, but you’ll have plenty enough for watching a movie on an airplane.
. . . Brent Butterworth
brentb@soundstagenetwork.com