Wednesday, September 20, 2017

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I measured the Definitive Technology Symphony 1s 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 headphone amplifier. I moved the headphones around on the ear/cheek simulator to find the position that produced the most bass and the most characteristic response. As I usually do with on-ear ’phones, I used the Model 43AG’s clamping mechanism to ensure a good seal. This was a “flat” measurement; no diffuse-field or free-field compensation curve was employed. For all measurements, I used a cabled connection; adding a Bluetooth transmitter introduces latency and thus requires gating, which introduces anomalies into the measurements.

Frequency response

This chart shows the Symphony 1s’ frequency response with noise canceling (NC) on. It’s unusual in that the bass response keeps rising all the way down to 10Hz. Also, most of the measurements of closed-back headphones that I’ve taken show more energy between 100 and 500Hz. I’m not sure if this is good or bad, but these two attributes do suggest that the Symphony 1s’ bass might sound a little unusual. This chart represents the best channel matching I could achieve, but I rarely take points off on this because the positioning of the earpiece on the simulator has such a big effect on the measurement.

Three modes

This chart shows the frequency response of the Symphony 1s in their three wired listening modes: passive (power off), active (power on, no NC), and NC. Obviously, the sound changes significantly from passive to active to NC modes, but this is common among headphones with these options, and with many, the differences are larger. Active mode seems to have more bass resonance (“hump”) than NC mode, and a little more treble response. That’s surprising, because the bass sounds substantially more prominent in NC mode. It’s likely that the extra treble in active/no-NC mode makes the sound thinner than in NC mode.

Frequency response

Adding 70 ohms of output impedance to the V-Can’s 5 ohms, to simulate the effects of using a typical low-quality headphone amplifier, had no measurable effect in the Symphony 1s’ NC or powered mode (which is why I don’t show it here), but in passive mode it boosted the bass by 2-3dB and the treble by about 1dB, effectively increasing the Symphony 1s’ midrange dip.

Frequency response

This chart compares the Symphony 1s with two other noise-canceling headphones -- Bose’s QC25s and PSB’s M4U 2s -- all with NC on. The Boses are widely considered the market leader in noise canceling, and the PSBs have won nearly universal praise for their sound quality. The big difference is that the DefTechs have a midrange dip of 5-10dB between 700Hz and 2.3kHz. Don’t be too quick to condemn them for this -- lots of well-regarded headphones show a similar midrange dip.

Waterfall

The Symphony 1’s waterfall plot, shown here with NC on, reveals a few minor resonances between 2.5 and 10kHz, but these are well damped, and die out in just a few milliseconds.

THD

The Symphony 1s’ total harmonic distortion (THD), shown here with NC on, is insignificant.

Isolation

In this chart, the external noise level is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. For reference, the drone of jet-engine noise in an airliner cabin is typically between 50 and 200Hz. For comparison, I’ve included in this chart the measurements of the PSB M4U 2 and Bose QC25 headphones. With NC on, the Symphony 1s’ isolation is about average for NC headphones.

Impedance

As is usual with active headphones, the Symphony 1s’ impedance is high in powered/NC mode, though from this test I often see impedances of 1000 ohms or more. In passive mode, the DefTechs’ impedance runs between 30 and 60 ohms with a bit of phase shift, which is why the response changes with high-impedance sources in passive mode.

The sensitivity of the Symphony 1s, measured between 300Hz and 3kHz with a 1mW signal and calculated for 32 ohms impedance (my default when measuring powered headphones), is 94.7dB in passive mode, 105.2dB in active mode (NC on). Thus, when their battery runs down, the Symphony 1s will likely play reasonably but not very loud with a smartphone or tablet used as the source.

. . . Brent Butterworth
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