Can't decide if you want a wired or wireless pair of headphones, or one with active noise cancellation or without? If you've got the cash, you can have it all with the Sennheiser MM 550-X (£350), an extremely well designed set that covers practically every situation you'd ever encounter. It also sound pretty amazing, which helps.
Design, accessories and controls
The MM 550-X is a closed, around-the-ear design, and weighs 180 grams with the battery inserted. Both the earcups and the headband are heavily padded, and the soft padding feels quite comfortable. You get quite a lot of passive noise cancelling just from the tight seal the earcups form with the MM 550-X on your head. The headset is also a bit lighter than some larger pairs of wired headphones, like the venerable Sennheiser HD 650 and the Bose QuietComfort 15. Even so, it feels quite rugged; the plastic, folding hinges in the headband and around the earcups in particular look especially sturdy.
Sennheiser packs in a number of accessories here, too. In addition to the headphones themselves and the rechargeable battery, you get a USB charging cable, a power plug with adapters for different countries, a stereo audio cable (2.5mm to 3.5mm) for use in wired mode, a quarter inch headphone adapter, an in-flight adapter for use with double mono jacks on airplanes, and a rugged, zippered cloth carrying case. The manual comes as a PDF file burned onto an included CD.
The controls are extremely easy to use even with the headphones on your ear. The centre of the oversized five-way control pad on the right earcup is large enough for an entire fingertip, and features a raised plastic circle around it, so that you can't miss it. Top and bottom control the volume, while left and right skip to the next track in either direction, all on devices that support remote control over Bluetooth. You can also hold down the Skip buttons to fast-forward or rewind the track. The bottom of the right earcup houses Bluetooth, NoiseGuard, and SRS buttons (more on these in a moment), as well as a 2.5mm jack for using the headphones in a wired configuration. The left earcup only has a covered micro USB charger port.
Hold down the multifunction button for five seconds, and the MM 550-X goes into pairing mode. You'll never miss that; not only does the control pad pulse red and blue, but the SRS and Bluetooth buttons light up as well. I had no problem pairing the MM 550-X with an Apple iPhone 4. The Multifunction button also handles accepting, rejecting, and ending calls, and you can transfer the ongoing call between the phone and the headphones – or activate voice dialling by pressing and holding the Bluetooth button.
Sound quality and noise cancellation
Sennheiser's big pitch with the MM 550-X is apt-X audio encoding, which the company claims delivers wireless audio quality that is indistinguishable from the highest quality wired connection. Here's the trick, though: It only works if the sound source also supports apt-X. My iPhone 4 doesn't, but even so, I heard pristine audio in both wired and wireless modes. Both modes sounded virtually identical. I detected the tiniest hint of compression artifacts in wireless mode, in a slightly more closed soundstage. There was also a touch of occasional harshness, but I had to strain to hear it.
Pressing and holding the NoiseGuard button for two seconds activates the MM 550-X's active noise compensation system. It does this via a pair of tiny mics near the earcups that focus on ambient noise in the 20Hz to 1KHz range, and then use this noise as a template for generating an opposite wave, 180 degrees out of phase, to cancel the noise out. Press and hold the button a second time, and you'll turn NoiseGuard off.
With NoiseGuard switched on, the MM 550-X did a nice job of muting some strong office fans of various sizes. But you could still hear them more than you could with, say, the Bose QuietComfort 15. My main issue with NoiseGuard, though, was the reduction in fidelity; it turned the MM 550-X into an average pair of headphones you could buy for less than £50, in terms of sound quality. The warmth disappeared, I heard the typical artifacts in the midrange that often betray active noise compensation, and nearly all of the MM 550-X's marvellous bass extension vaporised. Bose QuietComfort models are by no means musically neutral, but they seem to do a better job of compensating for the active noise cancellation circuitry.
TalkThrough and other features
The TalkThrough function takes the audio recorded from the tiny mics and actually pumps it into the earcups. This way, you can hear what's going on around you without removing the headset, while still filtering out more distant background noise. You activate this by just briefly pressing the NoiseGuard button, instead of holding it down. When you do this, the music is paused so you can talk to someone in the room; turn off TalkThrough, and the music will begin playing again.
Then there’s the SRS button. With SRS WOW HD engaged, the highs are exaggerated in the 5KHz region, as if you're listening to a cassette on a car stereo, with little top-end air or detail around them. The button also amplifies the bass even further, but with extra mud, as if the “bass” control on a cheap mini system is turned up without much in the way of granularity. My recommendation: Leave it off.
In my tests, the MM 550-X wasn't that great at handling voice calls. I heard the other caller, but their voice sounded computerised, and I could barely hear my own words because of the tight seal of the earcups. I was hoping TalkThrough would be a good workaround for this problem, but if you activate it during a voice call, it does the same thing as when there’s music playing, muting the audio source and turning on the external mics, so you can't hear the caller anymore.
According to Sennheiser, the battery should provide 8 hours of continuous listening with Bluetooth and NoiseGuard (active noise cancellation) enabled, 10 hours over Bluetooth without NoiseGuard, and 20 hours in wired mode with NoiseGuard activated. It will last forever in wired mode without noise cancellation, because then it works just like a regular pair of headphones. The LED indicator flashes red when the battery is almost dead.
One other minor quirk: You need to take care when disconnecting the micro USB charging cable. Otherwise, you'll pull the battery clear out of the left ear cup, which isn't good if you don't notice it, and then leave the house without the battery inside. But there's a reason for this design: You can charge the battery pack either when it's inside the earcup or out, since the battery itself contains the micro USB charger port.
Overall, the Sennheiser MM 550-X is an extremely flexible set of headphones. You're paying for all this technology, of course, and not all of the money is going into the actual sound quality. The MM 550-X sounds good enough that you'll feel like it's money well spent, especially when using it wirelessly. Its active noise cancellation, while not class leading, is still fairly effective – but sadly, it messes with the overall sound quality. If you want the best in this department, and don’t need a wireless pair, then you’re best off looking at something like the older Bose QuietComfort 15.
If you don't specifically need Bluetooth compatibility or active noise cancellation, then you might find a better option elsewhere within the Sennheiser range. The Sennheiser RS 220 is pitched around the same price, and offers stellar sound and comfort, although it’s really designed for home use. At around £120, the Sennheiser MM 100 is a more affordable and practical wireless option that still delivers solid performance.