With 50mm neodymium drivers, the Philips Fidelio X1 headphones have larger units than the average - even the Sennheiser HD 700 use "standard size" 40mm drivers. Only a few pairs of dynamic headphones have larger drivers than this, such as the Editors Choice-grade Sennheiser HD 800 with their giant 56mm drivers.
Driver size isn't everything, but whatever special sauce has gone into their tuning has certainly paid off. The Philips Fidelio X1 bring the best bits of a open-back headphones - the wide soundstage, the articulate top-end and smooth presentation - without suffering from the negatives that sometimes come with the territory.
Open-back headphones can sound a little too laid-back, which might be thought-of as dull. However, the taut and punchy low-end here is much closer to what you might expect from a closed-back pair. It's also in better proportion with the rest of the sound when compared to the other Fidelio models, the Philips Fidelio L1 and Philips Fidelio M1. If anything we're surprised that Philips has managed to pull the Fidelio X1 out of the bag for so just £30-40 more than the L1.
Some of the characteristics of the series remain, though, and they may not please everyone. These are quite warm headphones within their category, with the low-end skew reaching up a little further than just the lowest frequencies. This leads to lesser sense of separation than something like AKG Q701, which are now available for around the same price. They are smooth and detailed, but Philips's main focus seems to be on making the Fidelio X1 enjoyable, rather than perfectly balanced or fiercely insightful.
There are times when the low-end gets close to being a little too big as well, especially compared directly to some of its £200-300 peers. These aren't quite the ultimate in audio from every respect, perhaps, but they are an absolute delight if you're after high-end sound that doesn't trade in all of its low-end thrills for definition and composure.
The Philips Fidelio X1 are among the best-looking, most comfortable open headphones you can get. They're made from top-quality materials and the cable is as easy to switch as cables get. Sound quality is excellent too, although they're best-suited to those who think that some expensive headphones trade in too much bass for the sake of sounding high-end.