Monday, January 22, 2018

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I measured the AKG N60 NC Wireless headphones using a G.R.A.S. Model 43AG ear/cheek 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 KB0065 simulated pinna for most measurements as well as the new KB5000 pinna for certain measurements, as noted. For Bluetooth-sourced measurements, 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.

Frequency response

The N60 NCs’ frequency response (taken with a Bluetooth signal with NC on) looks very by the book, with a rise in bass response at about 100Hz, a strong peak at 3kHz, and a weaker peak between 6 and 7kHz. The level of bass relative to the midrange and treble may be affected to some degree by the gating required for the analyzer to compensate for Bluetooth’s latency; the actual level may be a couple dB higher.

Frequency response

This chart shows the right-channel frequency response of the N60 NC Wireless measured with Bluetooth and NC on, and in wired mode with NC on and off. The difference in response between the Bluetooth and wired modes is negligible (and may be due entirely to response differences caused by the gating used for the Bluetooth measurement). The big difference is when NC is switched on and off: with no NC, the bass response is greatly reduced and the headphones are likely to sound thin. Although I don’t show it in this chart, I also measured the response of a wired connection, adding 70 ohms output impedance to the V-CAN amp’s 5-ohm native output impedance, but saw no notable change in response.

Frequency response

In this chart, the N60 NC Wireless is compared with the response of the original wired version, the N60 NC. It appears that the two headphones were voiced according to somewhat different philosophies.

Frequency response

This chart shows the N60 NCs’ right-channel frequency response measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna. (I’ll be switching permanently to the new pinna because it more accurately reflects the structure and pliability of the human ear. I include this chart mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review for at least the next year before I start using only the new pinna.)

Frequency response

This chart shows the N60 NCs’ right-channel frequency response compared with the FRs of three other NC headphone models: the Bose QC35, the PSB M4U 2 (generally considered to rank among the best-sounding NC headphones), and the Sennheiser HD 4.50 BTNC. Except for the AKG’s reduced bass response (possibly due to its on-ear design; the other models are over-ear), its response is within the norm for headphones of this type.

Waterfall

The N60 NCs’ spectral-decay (waterfall) chart shows just a single, very narrow, low-magnitude (-40dB) resonance at 3kHz; this corresponds with the headphones’ lower-treble response peak and won’t be problematic.

THD

The N60 NCs’ total harmonic distortion (THD), measured with a wired connection because the Clio 10 FW’s sine sweeps can’t accommodate Bluetooth’s latency, is effectively unmeasurable, swamped by the measurement’s inherent noise. This is outstanding performance, especially for relatively small on-ear headphones.

Isolation

In this chart, the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. (Note that I recently switched to measuring at a level of 85dB instead of 75dB; this doesn’t change the way the isolation curves look, but an 85dB level lets me get better measurements of NC headphones, which demand a lower noise floor.) The isolation of the N60 NCs is basically about average for NC headphones, but a little above average for an on-ear model -- better than the original N60 NC (which has much smaller earpads), with about a 15dB attenuation right where airplane cabin noise is usually worst: 100-200Hz.

Impedance

The N60 NCs’ impedance magnitude is very high, which is common for active headphones, and measures the same whether the headphones are powered on or off. I expect that all the high impedance in the bass is the reason for the weak bass response in passive wired mode. The phase shifts from 0° at 20Hz to -72° at 20kHz, which doesn’t matter when the headphone is in active mode.

The N60 NCs’ sensitivity in wired mode, measured between 300Hz and 3kHz with a 1mW signal calculated for 32 ohms impedance, is 104.1dB -- they’ll easily play very loud when you plug them into an airplane seat’s headphone jack.

. . . Brent Butterworth
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