Having listened to a lot of high quality over the ear headphones recently, such as Sennheiser's own PMX 200, we were interested to see what their latest earbuds had to offer. Generally speaking earbuds provide inferior sound to a good pair of full sized headphones, simply due to smaller drivers and the MX 55s continued this trend. They offer sound quality well above that of the average earbud, but did still exhibit some traditional earbud flaws including a lack of bass and a slightly thin sound.

The real selling point of this model is Sennheiser's new design, which adds two small wings above the main headphone bud. These wings slide into one of the cavities in the ear and help hold the buds in place. A common problem with regular earbuds is keeping them in position and Sennheiser's solution works quite well to counteract this. We found it a little uncomfortable at first, but you quickly get used to it, and the added stability is a big bonus, particularly if you mostly listen to music while on the move.

The sound was pretty much what we expected of a high quality pair of earbuds. It will satisfy the average listener, but the more discerning consumer will probably want an over the ear model. The audio is quite detailed, with great separation between the mid and treble range sounds. The mid range is particularly well presented, with a smooth texture that suits a wide variety of music.

However there was a disappointingly low level of bass. Most music we tested with came up lacking in the lower registers. It didn't extend deep enough, nor have enough impact for the bass to really be felt and left the sound a little thin. The lack of bass also really emphasized the strength of the MX 55's highs, giving them quite a bright sound, which some people prefer. Overall we were quite pleased with the sound quality, particularly for a pair of earbuds, although they aren't quite on the same level as their over the ear brothers. The issues we had with them were issues common to all earbuds, so it is hard to be too critical.

Designed as a 'street' model the MX 55 have a fairly nice style about them. The default colours are dark blue, with a silver rim, but Sennheiser include interchangeable face plates for the fashion conscious buyer. There are also multiple pads included for both the earbud tip and the extra stability wing, allowing you to shrink or enlarge them to fit your ear.

We found their sound leakage levels to be about average. Earbuds have an open design, and will leak sound to those around you; thus they are not ideally suited to quiet environments like libraries.