Performance

These headphones are one of the top performers in the current Ultrasone lineup. In order to test these headphones properly I tried them with all of my three different home amplifiers, right from my Travagan's Green through the Octavart to my current favorite the Head-Direct EF1 with a Sylvania tube. As far as reference headphones go I pulled out some of my fullsized headphones. These include the following: AKG K701, Sennheiser HD 580 (Mods: HD 600 grills, de-foamed, upgraded cable), Ultrasone HFI-680, Grado SR-60 (Mods: Upgraded cable, new grills, added dampening material). Before beginning my listening tests I burned in the headphones for well over 200 hours, in order to be sure they would perform their absolute best or reasonably close to that.

The first thing that hits you when you enter the Ultrasonian world of sound is the low end. These headphones have a lot of bass and the extension is simply superb. It simply puts all the other headphones I own to shame. The bass is big, but I would not define it as bloated since it retains an incredible amount of detail even at extremely low frequencies. Add the fact that it has a really good impact and you are in for quite a treat. The only slight issue with the bass is that the ear cups are somewhat resonant and add a longer decay than usual. Nothing horrible, but still something you should consider. If you are a detail freak this might throw you off a bit. It might be fixable by adding some dampening material to the insides of the cups, but this will most definitely void your warranty.

Moving on up from the bass to the midrange and the Ultrasone PRO900 become an increasingly interesting set of headphones. The midrange is slightly recessed, but with loads of details and it is a bit on the warm side. It is a shame that it gets pushed back in the mix due to the frequency response of the headphones. Compared to the HFI-680s the PRO900s have way more bass and the midrange is not quite as dominant. In terms of details the PRO900s are way ahead no matter how you look at it. The bass is bigger but packs a better punch and the extension is a wee bit better as well. Midrange wise the PRO900s are warmer and give a better spacious presentation of the music. The general sound of the PRO900s is more refined or composed if you will. The performance of the PRO900s is nothing short of fantastic, they handle drums and the bass like a champ. Add the fact that they control details nicely and have a quite airy midrange for a closed back headphone.

One of the few problems I noted during my listening tests was a somewhat over emphasized upper midrange which can cause them to sound sibilant on some tracks. They are not the most sibilant headphones I have tried, in fact far from, but still if you cannot stand sibilance then you should think twice especially when considering the hefty price tag.

In comparison to my AKG K701s the PRO900s have a more intimate sound with a lot more and better defined bass. In fact the PRO900s do just about everything else a tad better with one exception namely the highs. The AKGs are just a tad more refined, but it is almost too close to call between the two, also both the AKG K701s and the Sennheiser HD580s have a more forward midrange with less bass emphasis. The more forward midrange presentation of the two open back headphones is something I prefer to the more laid back and intimate midrange of the PRO900s, but that is up to your personal preference. One aspect where the open back headphones do not even come close to the PRO900s quality is in the bass department, the PRO900s are so close to perfect.

The PRO900s have a very intimate and engaging sound. Add that to the fact that they have an extraordinary amount of details and I think it is pretty safe to say that most people will find them delicious.

When it comes to amplifier requirements the PRO900s are not the trickiest headphones out there to power. They sounded really good on both of my solid state based amplifiers, and while the Head-Direct EF1 with a Sylvania 12AU7 tube added some warmth and brought forward the midrange and aided the soundstage, the gain was just too high for most newer CD recordings. In terms of synergy I really liked it with the EF1 because of the slightly more forward midrange, the gain issue with regards to the EF1 is solved with the newer version with better volume control.

Durability

The build quality is really good. Like all newer high end Ultrasone headphones these are made from a tough kind of plastic and all the joints are quite heavy duty. When it comes to the cable not only do you get two, they both feature some of the best plugs available. The normal non-coiled cable has a nice soft yet durable cable jacket which is less microphonic than that on the HFI-680s and feels much more durable.