You can usually separate MP3 player owners into three segments: those who are obsessed with getting the ultimate in sound quality from their players and will stop at nothing to achieve it; those who care but don't want to spend too much cash; and those who listen to the $5 earbuds that come with their $200 iPod, and only replace them when they break.

Sennheiser's latest headphones, the CX400, are aimed at the middle group. Though they're not quite in the same territory as some of the top-end Shure or Etymotic headphones Riyad has reviewed in recent times, they are good enough to reward the extra investment over a pair of $20 upgrades - and they're certainly better than the bundled earphones you get with most players.

They're the successors to Sennheiser's popular CX300 headphones, boasting improved bass, clarity and all the usual stuff you expect from an upgrade such as this. I've yet to find a pair of headphones that can match Shure's offerings - such as the SE210s or even the older E2cs - at this sort of price, so I was interested to see how Sennheiser's new babies measured up.

In the flesh, they're certainly an impressive pair of headphones: the build quality seems pretty good - rubber sheaths protect the cabling coming from each earpiece - and they certainly look a lot nicer than the bulbous offerings that Shure offers in this mid-price sector, with silver sealed bodies and stainless steel rings wrapping each unit at its widest point.

They're also among the most comfortable noise isolation headphones (canalphones to be more precise) I've ever worn. With most phones that go right down inside your ear canal, there's usually a breaking in period where you get used to the way they feel, and the rubber or foam adapts to the shape of your ears - but that's not the case here. The CX400s felt comfortable right from the off - they're light and in my ears they hardly felt like they were there at all. And for anyone who the standard medium rubber flange doesn't fit, there are a couple of extra fittings in the box - a small and large pair. With the CX400s pushed as far down inside my ears as they would go, noise isolation was pretty decent too: on a noisy London tube train I was able to listen to quiet classical and jazz music without having to turn the volume right up.