A 300-ohm open-back that thirteen independent measurement fixtures draw the same way: sub-bass rolling off below about 100 Hz, a mild upper-bass shelf, midrange essentially on target, and a presence region that falls away from 5 kHz up. Almost everything reviewers argue about sits on top of that one curve. Most read the tonality as warm of neutral and natural — it is the single most agreed-on thing about the headphone — and the midrange is the headline strength. Comfort is a near-consensus strength at 260 g, and it is open-backed, so it isolates nothing. The treble is the defining split: roughly two thirds of the weighted sources call it veiled, dark or short on air, a third call it smooth and fatigue-free, and both are describing the same measured dip. Bass divides three ways — rolled-off, sufficient, or bloomy — and the soundstage is far more often called intimate than wide. Liveliness splits on amplification, imaging on whether you count separation or placement, detail on how much the smoothed top end costs you, and build on whether 'plasticky but repairable for twenty years' reads as a strength. Two things the measurements settle that the forums don't: pad wear quietly removes up to 6 dB of upper treble, and the two classes of test rig disagree with each other by 12 dB in exactly the band the veil argument lives in.
About this product
Open-back, 300 ohms, in production since 2003 and still sold by Sennheiser at $579.95 — though the street price on Amazon is about $322. Not the brighter HD 600, and not the lower-impedance HD 660S/660S2. The Drop HD 6XX is the same headphone on the older tooling — Sennheiser says only the design changed, and six measurement rigs that hold both put them within about a decibel of each other — but since Drop wound down in early 2026 the 6XX is sold by Sennheiser directly at $219.95 rather than Drop's old $199. Units vary: there have been at least six quiet revisions (black-paper, black-silk and silver-screen baffles), a cosmetic 2019 retool, and reports of current stock being made in Romania rather than Ireland with different pads.
The HD 650 is the headphone the hobby keeps coming back to. Sennheiser's open-back reference arrived in 2003 as the warmer sibling of the HD 600, and two decades on it is still the default first 'serious' pair — a fixture of mixing desks and audiophile starter racks alike. A 300-ohm driver behind velour pads, repairable from off-the-shelf spares and kept perpetually affordable by the acoustically near-identical HD 6XX, it has outlasted most of its rivals by simply refusing to go away.
It also carries more lore than almost any headphone made: the fabled 'Sennheiser veil', a reputation for needing a real amplifier, and a thousand threads insisting it is either the last headphone you'll ever need or quietly boring. Thirteen measurement rigs now hold it, and they agree on the curve almost exactly — which makes the HD 650 the rare case where you can watch an argument and check the physics underneath it at the same time.
