In a recent reddit AMA Tyll mentioned that Philips offerings have surprised him the most in recent years. Listening to the new Fidelio earphones, I have to agree---Philips did a spectacularly good job with the tuning. Both the S1 and S2 sound clear and accurate with just the right amount of bass kick. The low end extends nicely, with very mild overall boost and medium impact reminiscent of the VSonic GR07, an IEM highly renowned in audiophile circles for a good two years now. Here, the pricier Fidelio S2 seems a little more boosted than the S1, resulting in a slightly fuller and warmer overall sound.
The mids on both earphones are crystal clear, with resolution to rival accuracy-oriented in-ears from VSonic and HiFiMan. The lack of bloat helps, allowing the deep bass of the Fidelio earphones to shine and keeping the midrange completely clear of bass bleed. Treble presence is good too---the earphones aren't lacking at the top end for my tastes, and I've been known to enjoy a more energetic sound. At the same time, the treble is free of grain and harshness. In comparison, the VSonic GR07 sounds a little peaky and sibilant while the HiFiMan RE-400 and RE-262 are smoother and more laid-back. The S1 and S2 are again very similar here, with the pricier model offering slightly flatter-sounding treble and an airier sound. The presentation is also very similar between the two, boasting good width with average depth and reminding me of Sony's dynamic-driver EX600 and EX1000 models.
Curiously, the Fidelio earphones are not super efficient for a portable audio product and take more power to reach listening volume than much of the competition. This isn't a problem except for those who gauge sound quality by maximum attainable volume - there's still plenty of headroom with portable players. The earphones aren't picky with sources, either, and sound decent enough from a sub-par Android phone.
There is one small caveat with the both the S1 and S2: they require a very good acoustic seal to perform their best. This is true for almost all IEMs but because of the near-neutral tuning of the Fidelios, there's not much room for error. The large size of the housings and limited insertion depth play a factor as well. Without a good seal the bass quantity drops, the treble sounds a touch hot and spitty, and the presentation loses its depth. Here, the pricier S2 model has an advantage with its extra eartips. I was able to get a great seal right away with the included Comply Ts-series foam tips. The S1, which only comes with the cheaper S-series tips from Comply and fewer silicone tips, was tougher to fit out of the box.
It's not very often I get blindsided by a new release from a major player but the Philips Fidelio earphones caught me completely off guard---the first time I heard of them was when Tyll brought pre-production samples back from January's consumer electronics show. And boy, am I glad he did.
Traditionally, I have favored balanced armature earphones around the $100 price point---they tend to be clearer and more balanced-sounding than entry-level dynamics. The Fidelios, however, are part of that rare breed of accurate-sounding dynamics that simply leave nothing to complain about. The pricier Fidelio S2 model has a nicer finish, extra eartips, and sounds marginally better but at $99.99, it's the S1 that is going on the InnerFidelity Wall of Fame for delivering top-tier sound at a price that's far from.