Review: HiFiMan HE-6 Headphone and EF-6 Amplifier Page 3

Measurements: HE-6

To measure the HE-6’s performance, I used a G.R.A.S.43AG ear/cheek simulator, a Clio 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 experimented with various positions of the HE-6’s earpads on the ear/cheek simulator and settled on the positions that gave the most representative results.

The HE-6’s frequency response measurement is unusual among headphones in general, but comparable to what I’ve measured from HiFiMan’s other planar magnetic headphones. The response up to 1 kHz is nearly flat, rising to a strong peak between 3 and 6 kHz, with a much stronger-than-average upper treble response. Adding 70 ohms output impedance to the V-Can’s 5-ohm output impedance to simulate the effects of using a typical low-quality headphone amp has no significant effect on frequency response.

To see how the HE-6 compares with the HE-500, I measured the right channel of each headphone and put both of the measurements on one chart. The frequency response curves look very similar in shape, but the HE-500 has a bit less low bass response and its treble peaks are somewhat more damped.

Total harmonic distortion (THD) at 100 dBA is rather high. Below 1 kHz, it runs around 2% to 2.5%, rising to a max of 6.6% at 1.3 kHz. The impedance shows that the HE-6 is practically a purely resistive load, measuring dead flat at 54 ohms with no phase shift. Isolation is practically nonexistent, so external sounds will be heard very clearly, but this is the norm for open-back headphones.

Average sensitivity with a 1 mW signal at 50 ohms rated impedance is extremely low: 81.3 dB from 300 Hz to 10 kHz, 81.1 dB from 300 Hz to 6 kHz.

Measurements: EF-6

Frequency response

20 Hz to 20 kHz, +0/-0.05 dB

Output power (1% THD)

610 mW at 32 ohms

210 mW at 250 ohms

Output impedance

23 ohms at 1 kHz

S/N ratio (1 mW, A-weighted)

-60.2 dB

Total harmonic distortion (1 mW/1 kHz)


To measure the EF-6’s performance, I used my Clio FW and NTI ML-1 audio analyzers.

Into a 32-ohm load (a common impedance for passive headphones), with volume set at maximum, the EF-6 delivered 490 milliwatts at 1% THD at the 0 gain setting, and 610 mW at the 10 gain setting. Into a 250-ohm load, I got 160 mW at 0 gain, 210 mW at 10 gain. HiFiMan’s Bian told me that the company measured the EF-6’s rated output power of 5 watts/50 ohms at 10% THD, but I wasn’t able to duplicate this result. Note that with a typical headphone, 1 mW is enough to deliver a loud volume, and even the low-sensitivity EF-6 requires only about 30 to 50 mW to achieve a loud volume.

The frequency response of the EF-6 at 1 mW into 32 ohms measures pretty much dead flat, dropping just -0.05 dB at 20 kHz. I did get a tiny wrinkle right around 60 Hz in the left channel, which could be a trace of hum from the power supply. Results into 250 ohms were slightly better, down just -0.03 dB at 20 kHz.

Output impedance at 1 kHz measured 23 ohms. 

Bottom Line

When concocting my concluding thoughts about the HE-6 and EF-6, I think I can understand what a writer for Car and Driver goes through when asked to test-drive a $400,000 Ferrari. It’d be easy to dismiss such a car as excessively expensive. . . except that it’s just so great.

The HE-500 is a fantastic headphone: great-sounding, much easier to drive, and 46% less costly than the HE-6. But the HE-6 is clearly better. Likewise, the EF-6 is very expensive and, unlike many lower-cost amps, doesn’t have a built-in DAC. But once you hear it what the EF-6 can do with the HE-6, it seems essential rather than merely expensive.

The HE-6 and EF-6 are definitely pricey. But what price excellence? As Will so aptly put it, “Every minute you spend with them is quality time.”

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