For some reason I recently decided that my 2 decade old old Senn HP 25s are in need of a much deserved rest, especially after I recently acquired a DAC/headphone amp (Beresford Bushmaster). As the headphones were just for home use, I just wanted the best sound per £, hoping for a more open sound than my old Senns, with better bass (not more bass) better soundstaging and a less congested sound.
I saw the AKG K550/551's online and set up a demo. Knowing they were bound to be better than the old Senn's I set up a bunch of other demos first to prevent me from buying the AKG's straight away.
Here's what I found-
*What follows is in no way meant to be exhaustive or authoritative, and as a casual and occasional user of this forum I bow to all the true mighty audio dons who post here, likewise I apologise if I offend anyone with the headphones listed that I briefly critiqued and found wanting, whether correctly or not.
Source material was a combination of files on the dealer's Sonus via my DAC, cd's via Arcam FMJ with headphone out, and iPhone 5s 256bit AAC, tracks were a combination of OST, (Solaris) electronica (Boards of Canada), 70's rare groove (Fred Wesley), alt rock (Radiohead/Mazzy Star/Echo & the Bunnymen), & classical (Vaughn Williams). I didn't eq anything.
In very short order (lunch break) I listened to (via DAC/Sonus)
Kef M500 - beautifully made, but sounded a bit like the audio equivalent of a bonsai tree-exquisite but without the scale to really excite. What felt like a low clamping force probably didn't help. Perhaps they just didn't fit.
Grado SR125i-looked forward to these as I like weird, retro, arcane takes on things. Pad wise I knew I couldn't live with them immediately and as others before may have noted, whilst there is some magic in the top end it felt like it could be easily overwhelm/become sibilant, with the lower registers not quite keeping up in terms of balance. I'm sure the more expensive models are special.
Senn Momentum on ear/over ear-I tried both of these and really couldn't see myself ever enjoying them, the mid bass felt too dominant preventing me from hearing anything else and leaving me wanting some decongestant from the pharmacy opposite. Next.
B&W P7- I was looking forward to these after trying the little brother sometime ago and being underwhelmed at first then retrospectively thinking it may have been due to them being more neutral than I'm used to. The P7's were certainly different, bigger soundstage (that I didn't necessarily enjoy as much as I'd have thought) with what sounded like a sound signature that projected some treble and all the bass to the point where I couldn't really enjoy the music behind the artifice. They may have had a textured bass and good sub bass for all I know but the lack of balance with the mids (for me) meant they sounded one note, fatiguing and uninteresting.
Then I tried the AKG K550 at another dealer (ARCAM CD+ iPhone 5s), and there followed much head scratching. There was some openness and a pleasing soundstage as per reviews, but it felt like all the bass was missing. Plus they felt like a pair of trousers that were too big. I tried the Solaris soundtrack, with its sub bass. Where it should have kicked in, there was nothing, not even a hint. The biggest diameter headphones of the day had the least bass. I tried some Grado SR60s and Momentums that were lying there just to be sure I wasn't imagining it. I wasn't, the 550's I tried weren't just bass neutral, they were anaemic. I played with fit, rotated pads, fiddled with the headband, and bid these much anticipated cans good night and left disappointed and empty handed. I suspected fit issues but even with them pushed against my head the bass was absent. Maybe they were faulty.
I regrouped, researched and found favourable reviews of the K545. Many noted the relative lack of bass on the K550 and claimed that the smaller model redressed the issue with some caveats. Plus the 545's looked like military issue items (good). I then read up on the NAD HP50 and while their looks didn't appeal (a bit lifestyle) I lined up an audition pair. Instantly I knew I liked these-balanced, smooth, comfortable, and felt like total quality items. I had to leave the shop quickly to stop myself buying them until I'd heard the K545's. Keepers.
I brought the K545 demo home for the weekend (with lovely grey braided AKG cable sans iphone/android buttons), and plugged them into the DAC. The unit had some hours on it so burn in wan't an issue. As I listened it was clear that the wait had been worth it, my sound sig seemed all there, in the proportions that work for me and in new ways I hadn't anticipated.
I have never experienced articulate sub bass like this in a headphone. Ok, the bass that had dominated the P7s, the mid bass that killed the Momentums, would have helped with some of the dance music I listen to-some mid to upper bass energy is recessed, but this seems to let the sub bass and lower octave clarity breathe. The mids are clear, vocals engage, scale is present, the highs can lean ever so slightly toward aggressive and perhaps they don't extend as high as some, but the compromise is one I'm happy with. Comfort is good, I've worn these all day at work (I make documentaries), isolation fairly good, and I haven't had my hearing acuity fatigue in the way that spending hours in front of studio monitors just makes you turn the volume up.
Acid test- a brief trip back to the NAD dealer for a K545/HP50 face off. I only had a few minutes but I can honestly say the HP50's perform a neat trick of sweetening music which is seductive. They sound expensive, liquid, luxurious. The build quality feels better than even the P7's, and the earpieces rotate flat. But I think the liquid smoothness de emphasises some detail. A bassline on a Sebastian Tellier track (La Ritournelle) was gorgeous but missing its scratchiness. Plus they were £50 more. And the looks weren't for me. And K545 has sub bass. The NAD's would be a luxurious way to compliment the K545's but a luxury I can't justify.
The demo K545's were swapped for new ones, which during burn in seem to get worse before they get better (more congested sounding after 20 hours, opening up after 30-maybe it's just me). Problem is I keep staying up REALLY late listening to tracks I haven't heard for years.
I must say thanks to @dweaver for your many informative and interesting posts - and for taking time the time to evaluate the nuances of these cans vs the many others out there. I read this entire thread before pulling the trigger.