The Sennheiser HD650 has been around for a while and has certainly achieved a high reputation among both domestic and professional users.
It's a smart, no-nonsense model with oval earpieces which seem to fit snugly on every head we tried. There's plenty of depth to clear prominent ears and the velvet-lined earpads distribute the spring force from the headband, which at first seems rather high, very comfortably.
We had no discomfort over long listening sessions, though these do seem rather warmer on the ears than other models which give a less firm seal to the head and they sit securely enough to cope with sudden head movements. The lead is highly immune to friction noise, though the headphones sometimes squeak with facial movement, especially if one wears glasses.
Peering through the open-back of the HD650, there's a fine metal mesh, which is Sennheiser's way of damping the movement of the drivers and reducing resonance.
Distortion is also claimed to be particularly low, thanks to improvements in the magnet structure, while high-frequency extension is aided by the use of aluminium voice-coil windings.
Pair matching is claimed to be very good at ±1dB, a more plausible figure than some we've seen – bearing in mind that the smallest degree of misalignment on the head (or indeed on a test fixture) can easily contribute a few tenths of a dB of mismatch.
New levels of detail
There is no question that this is a very fine transducer. Like quite a lot of really good hi-fi, it doesn't always leap out on first hearing as an oustanding product, though it's clearly highly competent.
It takes a little listening to become aware of how good the sound really is, as its low-distortion nature shies away from loud or flashy display. As with every practical headphone, there is a little high-frequency coloration, but here it seems less obvious than is often the case, while the bass is warmly full but unexaggerated.
Above all, this is a very detailed transducer and it's possible to hear details which were previously unnoticed. A very familiar piano recording, for instance, suddenly showed up clearly where the instrument had a slight 'dead patch', the notes lacking some of the ring to be found across the rest of the range.
We had almost forgotten this aspect of the recording but, hearing it again, were reminded of the piano tuner's comment at the recording.
At the same time, there is none of the unnatural emphasis of high-frequency detail which can sometimes crop up with cheap headphones and is simply a symptom of over-bright balance.
There is a little high-frequency unevenness in the HD650, which shows up mostly in cymbals and similar sounds, but one soon gets used to it. Transients are crisp and well defined, while decay into ambience is very natural.
Stereo imaging is also very good, with very decent depth too, always a hard challenge for headphones since most of the cues are mangled in the absence of the crosstalk between loudspeakers which most recordings are created to rely on.
Among a number of fine headphones on the market today, this is a particularly attractive one.