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Reviewed on: SoundStage! Solo, January 2019

I measured the T60RPs using a G.R.A.S. Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, 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, with an Audio-gd NFB-1AMP used for distortion measurements. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.

Frequency response

The above chart shows the T60RPs’ frequency response. This is a fairly typical measurement, except that the T60RPs show a response peak at 1.3kHz and a dip between 2 and 4kHz, while most good-sounding headphones show a dip around 1.3kHz and a peak around 3kHz.

Frequency response

This chart shows how the T60RPs’ tonal balance changes when they’re used with a high-impedance source, such as a cheap laptop or some cheap professional headphone amps. With the high-impedance source, there’s a roughly 1.5dB boost in the bass below 70Hz, which will be just barely noticeable.

Frequency response

This chart shows the T60RPs’ right-channel response compared with two moderately priced open-back models (the HiFiMan HE400i’s and the Massdrop-Sennheiser HD6XXes), as well as the AKG N700NCs, a new closed-back model said to deliver response very close to the “Harman curve,” shown in research by Harman International to be the preferred over-ear headphone response for most listeners. Besides the peak at 1.3kHz instead of 3kHz, the T60RPs have a little more bass than the open-back models, and less than the AKGs.

Waterfall

The T60RPs’ spectral decay (waterfall) chart shows a little bit of resonance in the bass, but overall it’s pretty clean, and doesn’t have the hash we often see with planar-magnetic headphones between 2 and 5kHz.

THD

Measured total harmonic distortion (THD) of the T60RPs is pretty high in the bass (note that I’ve expanded my scale from the usual 20% max to 50% max in order to show the result at 100dBA). I repeated this measurement with a different amp on a different day just to check it, but the result was comparable.

Isolation

In this chart, the external noise level is 85dB SPL, and numbers below that indicate the degree of attenuation of outside sounds. You can see that the semi-open-back T60RPs’ isolation is better than that of the open-back HiFiMan HE400i and Monoprice M650 headphones, but not as good as closed-back headphones such as the NAD Viso HP50s can provide.

Impedance

As expected from planar-magnetic headphones, the T60RPs are just about dead-flat in impedance magnitude at 49 ohms, with only a slight bump in the curve at 65Hz. The impedance phase is essentially flat, too.

Sensitivity of the T60RPs, measured between 300Hz and 3kHz, using a 1mW signal calculated for 50 ohms rated impedance, is 90.8dB, slightly lower than the rated 92dB. This is low enough that you’ll want to use a high-quality portable music player or amplifier; you could probably use the T60RPs with a smartphone or computer in a pinch, but they won’t sound very loud.

. . . Brent Butterworth
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