There's a version of headphone history where the HD 600 is a footnote — the thing Sennheiser made before the HD 650 came along and supposedly improved everything. That version is wrong. The HD 600, introduced in 1997, is the reference point. Everything else is a deviation from it.
Sennheiser had been making serious headphones for decades by then, but the HD 600 was the moment they figured out how to put a proper planar-like midrange transparency into a dynamic driver design. The 300-ohm impedance wasn't an accident — it was a statement. These are not headphones for your Discman. They want amplifier current, and when they get it, they open up like a window you didn't know was closed.
What You're Actually Hearing
The frequency response is about as flat as a dynamic headphone gets without laboratory equipment. The bass is there — it's accurate, not enhanced. The treble has a slight presence peak around 3kHz that took Sennheiser a few revisions to dial in, and by the late 1990s production runs they had it right. The midrange is the whole point. Vocals, strings, acoustic instruments — the HD 600 puts them in front of you with a specificity that makes most other headphones feel like they're describing the music rather than playing it.
The soundstage is wide for a closed-feeling headphone, which the HD 600 absolutely is not — it's fully open-back, with that distinctive blue-marbled grille that either looks elegant or looks like a shower drain depending on your mood. I've always liked it. It's honest about what it is.
Run a tape from a well-maintained B215S through a decent phono stage into something like a Schiit Magni or an old Marantz headphone output with some guts behind it, and the HD 600 will show you everything that deck is capable of. And I mean everything. If there's head gap azimuth drift showing up as a dulled high end, you'll hear it. If the bias is dialed exactly right and the tape is NAB-spec 10.5-inch reel at 15 ips, you will hear that too, and it will rearrange your face.
That's the honest caveat too, and it's a real one: the HD 600 has no mercy. It's not a relaxing listen if your source material is mediocre. A badly dubbed cassette, an MP3 rip of something that was already compressed, a receiver with a noisy phono stage — the HD 600 will make you aware of all of it, clinically and without apology. Some people want headphones that make their collection sound better than it is. These are not those headphones.
The cable is detachable, which matters because the stock cable is long and a little unwieldy. Third-party alternatives are everywhere and cheap. The ear pads wear out over time — the original velour goes flat — but Sennheiser still sells replacements, which in 2024 is almost a miracle of corporate behavior and worth acknowledging.
Used examples from the early 2000s are the sweet spot. Pre-2003 production, original drivers still intact, original pads replaced with fresh stock. You'll pay $300 to $450 depending on condition and whether the seller knows what they have. That's not cheap for headphones, but the HD 600 has been in continuous production for nearly thirty years for a reason.
It's not the most exciting headphone ever made. It doesn't have the low-end weight of the HD 650 or the almost supernatural detail retrieval of something like a Stax electrostatic rig. What it has is accuracy and honesty and the kind of even-handedness that makes it useful for actually understanding your equipment and your recordings.
Some gear is about the experience of listening. The HD 600 is about the music itself.