Sennheiser HD 650

Design

The HD 650s have better aesthetics and durability. The HD 555s are very plasticky and don’t inspire a lot of confidence in their ruggedness. The HD 650s have a much more solid construction.

Sennheiser HD 650	Sennheiser HD 555

Frequency Response

HEY, READ THIS: We have to start this section with a caveat. See, the HD 555 was one of the first headphones we ever tested (oh, nostalgia), so the graph extends all the way down to 20Hz. We stopped showing that part of the graph because our testing rig isn’t 100% accurate for that range. Just disregard the bit below 100Hz and you’ll be fine.

The HD 650s gain a tiny advantage on frequency response. The HD 555 had a slightly more erratic high end. The differences between the two are minor.

Sennheiser HD 650	Sennheiser HD 555

Distortion

The HD 555s’ graph is a bit misleading because, like the graph above, it includes data from the 20-100Hz range. Disregarding that chunk, you can see that the HD 555s still have slightly more low-end distortion than the HD 650s, but slightly less distortion overall. Basically, neither set of headphones has much distortion.

Sennheiser HD 650	Sennheiser HD 555

Tracking

The HD 650 gets a solid advantage here with an even tracking. The HD 555 has some issues with the high end.

Sennheiser HD 650	Sennheiser HD 555

Isolation

Neither set of headphones is a good choice if you’re looking for isolation.

Sennheiser HD 650	Sennheiser HD 555

Comfort

Both sets of headphones have very similar fit and padding type. They’re about the same in terms of comfort.

Wear
Sennheiser HD 650	Sennheiser HD 555

Verdict

While the HD 650s are a better set of headphones, they aren’t better by all that much. Most of their advantages come in the form of subjective qualities, like clarity and a larger, more open soundstage. In terms of our testing, however, they’re really similar. We recommend trying them on back-to-back and seeing if the HD 650s manage to strike you as worth the extra few hundred dollars.