The Sennheiser CX 300-II is a high-quality set of in-ear earphones from the German electroacoustics specialist.
Sennheiser has a deserved reputation for making consistently great professional and hi-fi headphones and earphones. And in the post-iPod era, it has met the portable player challenge with a wide range of earphones suitable for on-the-road listening.
The Sennheiser CX 300-II falls into the category of in-ear earphone - not in the old sense of sitting loosely in the outer ear, nor of the newer entirely-in-the-ear such as those pioneered by Etymotic Research. Instead they provide a comfortable fit with the aid of soft silicone rubber, with three different removable rubber buds included to suit different ear sizes.
Whereas the true in-the-ear designs can provide near-total exclusion from ambient sounds, these looser fitting types give a good degree of isolation without entirely shutting you off from the outside world. They are also more comfortable to wear, especially for those squeamish about inserting an earphone deep inside the external auditory canal.
Importantly for considerate commuters, these semi-excluding in-ear 'phones can be played at a reasonable volume on a quiet train, for example, without disturbing your neighbours - yet still allow you to hear the sound of traffic as you cross the road.
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In appearance, the CX 300-II look nearly identical to the iPhone-centric Sennheiser MM 50, but without the latter's important in-line microphone feature. And the sound quality is broadly similar - clear and incisive, well-damped bass and good upper treble extension.
Sit down and listen, though, and you'll find a mildly more refined sounding pair of earphones in the CX 300-II. While the MM 50 has good frequency coverage with punchy bass and a relatively unmuddled midband, the CX 300-II proved to be even more open in the mid.
The MM 50 in comparison is more mechanical sounding, with slightly raised hiss levels, and a harder mid. Bass is never far from dynamic and punchy but perhaps not as deep and smooth. Sounds of different musical threads can overlap more. The CX 300-IIs can have a better separation of musical lines and are slightly less sterile overall.
And strangely, despite the quoted specs, the Sennheiser CX 300-II earphones sounded less sensitive on our test iPod 5.5G. Sennheiser lists the MM 50 iPhone earphones with a characteristic sound pressure level (SPL) of 106dB, and the CX 300-II with 113dB - a huge difference in subjective terms - yet we found the mic-less Sennheiser CX 300-II 'phones somewhat less ‘loud', and warranted a nudge on the volume control so that we could enjoy all they could give.