The HE-6 offers exceptionally wide-range frequency response, meaning that it never sounds as if it is working hard to reach the highest or lowest frequency extremes. HiFiMAN’s HE-5LE was already very good in this respect, but the HE-6 is even better. You’ll appreciate this difference especially when listening to the HE-6 navigates the very highest overtones of treble instruments (percussion, strings, etc.), as it makes even the subtlest distinctions between “overtone signatures” plain as day.
Note, however, that the treble characteristics of the HE-6 are not necessarily ideal for all listeners, nor do they work out equally well with all amplifiers. The gist of things is that the HE-6 is, by design, capable of lightning-fast transient response, but that the “price” of this speed can be—at least with some amplifiers—a subtle tendency to overemphasize sibilant “S” sounds or the leading edges of treble transients. Happily, though, careful amplifier matching can make these faint traces of treble edginess disappear (or nearly so).
Down at the other end of the frequency spectrum, the HE-6 offers a terrific combination of low frequency extension, pitch definition, and dynamic clout, though the latter quality is, for obvious reasons, somewhat amplifier dependant. Synth basses, pipe organs, concert bass drums and the like are, quite simply, child’s play for this headphone. In the bottom octave and a half, the HE-6’s bass is a touch more powerful than that of the HE-5LE, but more importantly its bass transient speed and pitch definition are better, too—qualities you’ll soon notice if you listen to good recordings highlighting either acoustic or electric bass. From time to time I’ve heard some audio pundits complain that headphones can’t do “real” bass the way that great loudspeakers do, but the HE-6 emphatically can, reproducing low frequencies with better power, precision and control than all but the most capable (and costly) full-size loudspeakers.
What differentiates the HE-6 from the HE-5LE is the sheer ease and suppleness with which it probes the top and bottom octaves of the audible spectrum, although this might seem like we are splitting hairs, since we are basically talking about the difference between an excellent headphone and one that goes even further up the performance ladder.
Coherency was one of the HE-5LE’s strengths, and it is a strength even more fully realized in the HE-6. There is an all-around evenness and self-consistency about the HE-6’s top-to-bottom presentation that is a real joy to hear. The HE-6 never gives preferential treatment to one frequency band over another; instead, the HE-6 is—across the entire audio spectrum—one of those rare transducers of which you could truthfully say, “Hey, it’s all good.”
Perhaps the one area where the HE-6 most clearly distances itself from the HE-5LE involves resolution of low-level details. While the HE-5LE was and is a very high-resolution headphone, the HE-6 takes resolving power to a whole new level. Interestingly, though, this is a difference that impresses some listeners favorably (I’m one of them), but that leaves others a bit cold. Here’s why.
With the HE-6, it is almost a given that the headphone will consistently show you things about recordings—even familiar recordings—that you didn’t know beforehand. On one level, this can be quite exhilarating—kind of like finding a wealth of sonic treasures “hidden in plain sight.” In fact, once you get acclimated to the HE-6’s, it can be almost painful to switch back to most other headphones because you realize that the finest levels of detail, which the HE-6’s capture to effortlessly, have suddenly gone missing (at least in part).
But others listeners sometimes react differently to the HE-6’s heightened powers of information retrieval, perhaps because not all of the new information that the HE-6’s convey will necessarily be pleasing (although I find that more often than not the additional information is a good thing). Nevertheless, some listeners hear the HE-6 and acknowledge the things it does well, but then immediately gravitate back toward the slightly warmer, more comfortable, and more “forgiving” sound of the HE-5LE (or of other competing high-end headphones). My point is that the HE-6’s ultra high-resolution sound can be a double-edged sword, at least for some. However, if you love to wring the last few drops of nuance and subtlety from your favorite recordings, the HE-6 will give you what you seek and more.
I’ve found that an interesting side effect of the HE-6’s superior resolving power is the sense that this headphone makes it easier and more relaxing to do critical listening. I believe this is because the HE-6 makes it incredibly easy to see and hear how the inner workings of pieces of music fit together. There is none of that sense that one is almost but not quite catching the critical details as the music flows past, almost too fast to comprehend. Instead, with the HE-6 in play, everything is made explicit, clear, and easy to grasp—almost as though time has slowed down, so that you are able to grasp the subtle, intellectual or “inner game” aspects of music even as you allow their emotional effects wash over and through you. For me, this has become one of the greatest joys of listening through the HE-6’s.