It's been a week since I got my 990 pro's and while there was some initial sibilance I found fatiguing, that did not last very long. The burn in was unexceptional and subtle, a slight opening of the soundstage, a smoother and less grainy top end, and a smoother midrange. About what I remember breaking in my 880's 3 years ago. Contrast that with the Q701 which went from unlistenable to decent in just a few hours of listening and you begin to see how effortless the Beyerdynamic break in is.
And now in where is the part in which I rustle some jimmies if you will forgive my chanisms "Not trolling".
I like the 990's better than the 880......I know, it's sacrilage but I said it. I spent 3 years loving the 880 sound, the effortless extension, the flat frequency response, the uber transparency, the incredible comfort. In all of that time though the one thing that I would have changed, that I found lacking, was ample bass. Don't get me wrong, the 880 can extend down to 18hz easily. It's bass runs deep, smooth, and low, but sometimes I just want to be rocked, and the 880 is too neutral to beat my head into a pulp without some EQ.
The 990 is the first headphone in my collection to not be improved with EQ at all. There is literally nothing I would change about it's sound signature, it sounds perfect to me plugged in straight, no EQ.
It's the difference between listening fun, and critical listening. The 990 is a fun headphone, it's musical, it makes any music you throw at it come alive, and it does this without being boomy or veiled, without a bloated mess of a upper bass and midrange. It does it effortlessly and with that incredible sound comes those velour earpads that let me listen to it for hours on end. I don't even care that the Pro version of the 990's have too much plastic, or that the headphone cable is coiled, they are so much more fun than the 880 Premium I don't care about those things and I have found myself using it as my go-to headphone.
My setup runs something like this:
Audioengine D1 DAC going into a FiiO E9 desktop amp.
The 990 is about as power hungry as the 880 250ohm (they are the same impedance) and about 1/2 volume on the E9 is sufficient to blow my mind. I've listened to so many types of music on the 990's and I have yet to find any that didn't sound superb. There are so many similarities there with the 880 in terms of sound signature, and it has that Beyerdynamic high of silky smooth upper range treble without artifacting or grain, and a slightly veiled midrange but unlike the 880's (even the 600ohm ) the 990 goes into overdrive below 120hz with almost 10db of boost over my 880's. That sounds like over kill and anyone who's ever listened to the bass heavy models in the Sennheiser lineup is probably thinking they know how boomy that is going to be, but it's not. Even though it's as loud as something like the HD419 in the bass department, there isn't a HINT of muddiness, or boom.
The bass stays true to the 880's tight and dynamic response and with greater extension into the sub bass realm. It's perfectly capable of rendering the tight slap of a kick drum, the warm thump of a double bass, the sub bass of a dubstep song, or the nuanced reverb of a piano's 88th key. It is my ideal bass response, one I've been trying to create with EQ work on the 880 for 3 years, perfected with a straight signal in the 990.
My search for the headphone I can use the rest of my life is complete.