An unusual feature of the Sennheiser HD 650 headphones is that the cables can be unplugged for easy replacement should the conductors ever fracture under physical stress in future years. They are quite thick cables, too, and three metres long, terminating in a 6.5mm plug. The only accessory is a 6.5mm to 3.5mm adaptor cable so you can use the headphones with a portable device or a computer.
The headphones are an ‘open’ design, even though their velour-finished ear cups completely surround the ears, resting on the head. This means that your ears are acoustically open to the outside world through the body of the headphones. They aren’t really designed for use in noisy environments.
The headband imparts quite a bit of sideways pressure to the head, so they’re held securely in place. At first I thought they might become uncomfortable after a while, but even after a couple of hours the soft cushions ensured no discomfort.
Sennheiser claims an extremely wide frequency response (16 to 30,000 hertz), and they certainly sounded like there were no limitations. More importantly, the balance across the frequency range was delicious. The kick drum came with its deepest frequencies, often omitted by headgear, but the cymbals ticked and trilled with precision at just the right level.
These made headphone listening a pleasure. The 300 ohm impedance makes these headphones an easy load for all headphone amplifiers. The cheap ones on many MP3 players usually lose their bass into low impedances. However lower output devices just won’t develop high enough voltages to deliver high volume levels with these headphones. An iPod had just enough, but they are higher output than most portables.