Sennheiser MM 550-X Wireless Bluetooth Travel Headphones
Hailing from the same German labs that produced the world-renowned HD800, Sennheiser's MM550 represents the current pinnacle of Bluetooth audio. Its smooth, dynamic sound is audibly reminiscent of Sennheiser's house signature, and while its not quite a portable HD650, Sennheiser is making clear steps in that direction. Its bass is smooth and powerful, extending to 60 hz with good power and managing to lend warmth to the midrange without overshadowing details in instruments or vocals. Its midrange is forward but not aggressive; it is silky smooth, presenting vocals in exceptionally pleasing fashion and giving instruments plenty of room to breathe (for a closed headphone) without sounding overly laid-back. Treble is slightly laid back; those wanting a more aggressive sound should look into the more v-shaped UE9000, but the MM550 is certainly no slouch when it comes to detail, and lovers of Sennheiser's house sound are sure to be pleased. There is an SRS button that does increase treble and bass to give a more "exciting" sound that should please those not used to a HiFi sound, but enthusiasts will notice that it does have a mild negative impact on staging; if you buy the MM550 and find yourself reaching for this switch, you may consider returning them for the UE9000, which deliver a livelier sound with more treble and bass out of the box for about $200 less. However those in search of maximum detail and fidelity will likely still prefer the MM550.
Features abound: the MM 550 includes active nose cancellation and accompanying talk through feature, as well as the ability to use with a cable instead of Bluetooth. Its noise cancellation is not exceptional; this is perhaps the one underwhelming aspect of the MM550. It does a reasonable job of blocking outside noise for office or even plane use, but also degrades the sound quality noticeably, compressing the soundstage and muddying the frequency response with extra bass that eliminates the pleasant warmth and replaces it with muddy midbass and additional midrange grain. Highs also lose some of their air and, like the midrange, become a bit grainy. If you plan on using your headphones primarily in NC mode, the UE9000 or a wired set from Bose would be a safer choice... though they might not sound as good!
Noise cancellation aside, these are excellent headphones, and should make you happy if your primary desire is to be wire-free with your portable device, especially if your source supports the Apt-x codec, which takes the MM550-X's fidelity to an even more impressive level for a Bluetooth headset. Those using their 'phones primarily at home may want to look at the similarly a priced RS220 for a more spacious, realistic sound, but if you spend most of your listening time on the go, the MM550-X will make a great companion.