I measured the HD 800 S 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 Musical Fidelity V-Can and Rane HC6S headphone amplifiers. I moved the headphones around to several different locations on the ear/cheek simulator to find the one with the most bass and the most typical average response. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.
This chart shows the HD 800 Ses’ frequency response, which is typical for high-end open-back headphones: basically flat up to 1.5kHz, then rising to peaks at 2.7, 6, and 7.7kHz. That’s normal -- most good headphones have response peaks in these regions, and the one at 2.7kHz, in particular, is generally thought to help headphones deliver a more convincing illusion of hearing freestanding speakers in a room.
Adding 70 ohms output impedance to the V-Can’s 5 ohms to simulate the effects of using a typical low-quality headphone amp (which I can’t imagine anyone doing with these headphones) boosts the HD 800 Ses’ output between 30 and 300Hz by an average of about 1.5dB, which will make the headphones sound just slightly more full.
This chart compares the frequency response of the HD 800 Ses with two similarly priced open-back models: the HiFiMan Edition Xes and the Audeze LCD-Xes. Obviously, all three are much more alike than they are different, the HD 800 Ses roughly splitting the difference in the treble between the Edition Xes and the LCD-Xes.
The HD 800 Ses’ waterfall plot shows some extremely narrow, low-level (-40dB) resonances between 1 and 4kHz. These are fairly common with open-back headphones. When I measure open-back headphones, I pile denim insulation on top of them to minimize the leakage of sound into the room (where it could reverberate) and/or back into the headphones, so I don’t think these are room effects or leakage of outside sounds into the measurement.
The HD 800 Ses’ total harmonic distortion (THD) is unusually low except below 100Hz, where it’s higher than average. When I saw these results, and how smoothly the distortion increases with frequency, I thought the Musical Fidelity V-Can might be having a problem driving the HD 800 Ses’ unusually high impedance. So I switched to a Rane HC6S, a professional studio headphone amp that, by my measurements, puts out 3.1W into 32 ohms and 0.4W into 250 ohms. I got the same results with the Rane. By my measurements and calculations, the HD 800 Ses should have needed only 2.7mW to achieve the needed 20Hz output at the 100dBA measurement level, which is well within both amplifiers’ capabilities; it appears these headphones’ measured bass distortion at very high listening levels is indeed higher than normal. But despite listening at fairly high levels -- which I often do with high-quality headphones because they generally don’t fatigue my ears -- I heard no distortion.
In this chart, the external noise level is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. Like all open-back headphones, including the others represented here, the HD 800 Ses offer no significant isolation from outside sounds. I include the Audeze LCD-Xes’ isolation measurement so that you can see how the HD 800 Ses compare with a closed-back model.
The impedance magnitude of the HD 800 Ses is very high and above the specified 300 ohms, running from a low of 339 ohms to a high of 801 ohms. The impedance phase curve is reasonably flat, though not as flat as those of many high-end planar-magnetic headphones I’ve measured.
The sensitivity of the HD 800 Ses, measured between 300Hz and 3kHz with a 1mW signal calculated for the specified 300-ohms impedance, is 103.0dB. That’s high for high-end open-back headphones, but portable players and smaller headphone amps may still be unable to muster the additional 9.7dB of voltage output required to drive 300-ohm headphones, compared with typical 32-ohm models.
. . . Brent Butterworth