Headphone Reviews

Sound Quality
When first introduced, I remember the HD 580 as a spectacularly good sounding headphone. Headphones of that era were more often then not bass-shy and overly bright, and it was a great relief for me to hear a headphone that was warm and smooth. When the HD 600 came along, I felt it very similar tonally, but more refined and articulate. Comparing the two, it does seem to me that the 580 has a slightly grainier sound, resembling plastic in its character. Tapping on the outside grilles, the 580 is clearly louder with a distinct "tock" sound to it, while the 600 grille yields a softer and more damped "tick" when thumped. So I do think there's something beneficial in changing the outside grille to metal mesh for the 600/650.

The sound of the HD 600 is overall smooth and slightly warm sounding. Like most cans of its era, the sub-bass response is a bit weak and somewhat loose, yielding a mild mid-bass bloom to the sound. The transition from mid-bass to treble is very even and well balanced, though the top treble octave might be just a tad shy of neutral. I really think the "Sennheiser Veil" myth with these cans is mostly the result of being compared to the many overly-bright headphones in this category (Grado, Audio Technica, AKG).

The HD 650 is rather more problematic to me. While the sound remains very similar to the HD 600 and does seem a tad more refined, it also seems a bit warmer, lusher, and thicker...more "veiled" if you like. Yes, in this case it does seem to warrant the discriptor. Just a bit too much of good thing. I still think it's a great headphone and have no problem recommending it, but with a $100 lower price, and a more neutral and snappier sound, I think the HD 600 is the better buy.

All these headphones have a forgiving sound and will provide a very nice listening experience from most any source, but they also respond very well to improved sources and amplification. Quite high by today's standards with a 300 Ohm impedance, these headphones can be mated to headphone amplifiers of any output impedance for a potentially a good match. They'll deliver a very nice improvement with a swap to balanced cables, a good balanced front end, and balanced headphone amp. And they're an absolute joy when driven by OTL (Output Transformer-Less) tube amps like the Bottlehead Crack and Woo Audio WA3. This is a great headphone with which to become very familiar and use to evaluate upstream gear.

Summary
Yup, I'll say it, one of the worlds greatest headphones.

Lush and inviting, the HD 600 is simply one of the best buys in the world of audiophile headphones. Easily paired with just about headphone amplifier, they will sound good directly from the headphone jack of a receiver, and will improve nicely when combined with better gear. Going up on the "Wall of Fame" as the best open headphone in it's price range.

While the HD 650 is slightly more refined sounding than the HD 600, it's also a bit warmer and thicker sounding...yes, maybe a bit veiled. While I think these headphones are very good and are well worthy of recommendation, I find the HD 600 a bit more neutral, and at $100 less, a better buy.

Resources
Sennheiser home page, and HD 600 and HD 650 page.
Sennheiser download page for manuals and brochures for current and discontinued products.
Head-Fi "Appreciation" threads for the HD 600 and HD 650.