[kutizoltan83]

Alright guys, i gonna write some words about my AKG K551 headphones - which i sold...
 
I was a big fan of the AKG K550. I had a quite worn pair. I loved the soundstage and detailed sound of it. Highs were a bit harsh sometimes, but i prefer brighter sound signature and enjoyed it.
So i ordered a new K551 and wanted to use as a gaming-movie watching headphone, also for music listening at home.
 
The new K551's headband somehow was quite comfortable on my head. It was pushing the top of my head quite much after 20-30 mins usage. With my old K550 i didn't have this problem... Maybe that was a bit loose and stretched already...
 
The other problem i had was the sound quality. Actually i really enjoyed the "specious" sound right after my Sennheiser HD 25, but i couldn't wear this AKG for long listening sessions. (long i mean more than 1 hour)
The "treble spike" made my ears tired and combine this with the pushing headband it was a pain to wear these after 30-60 mins. Tho' it has a very clean and detailed sound, but somehow i liked my old K550 better. That has a bit warmer sound and didnt have discomfort issues.
Its quite strange, because everybody stated in reviews they are the similar, but i dont think this... I have read a article on the internet (comparint K550 and K551) and somebody measure the actual sound of these and they were different.
 
Also i found these AKG K551's weaker in bass. They are very similar to the AKG Q701 (i owned) which doesnt really have a big low end. (at least for my taste)
 
So sorry guys, but i wouldnt really recommend these new K551.
I dont know what AKG did, but these headphone become worst than the old ones. 
These are still a good pair of headphones for analytic sound lovers, but i do recommend the old version (K550) or maybe the Sennheiser Amperiors instead.

 

[deltawars]

Like kutizoltan83 said do NOT get the K551 the K550 are much better, i found this guide: https://tomigra.wordpress.com/2014/06/11/akg-k551-vs-k550-porownanie/comment-page-1/#comment-297
 
I do recommend checking out that guide but in case you don't want to read i copied this from the guide.
 
Characteristics of K550 compared to K551:

1. greater holography (three-dimensional)
2. larger scene from more distant from the listener audio presentation
3. more authentic, rich, resonant sound with a tangible and diverse sound
4. more dynamic / contrast (differences sound)
5. though more natural vocals withdrawn
6. brighter and more analytical
7. faster and more precise bass with more readable and more luminous structure sopranos
8. more air and freedom in the sound
9. holography and stereophony greater results in better readability tracks, instruments and separation (the details are more exposed)
10. more mikrodetali
11. sound more engaging, audiophile-profile, more analytical and tiring
12. higher class technically sound (especially in the aspect of holography and fidelity)

 
Characteristic of K551 compared to K550:

1. less three-dimensional sound
2. more concentrated closer to the scene of the listener's audio presentation
3. noticeable reduction in the depth of the scene and the flattening of the audio presentation
4. more dark and uniform sound, without distinction at the margins as in K550
5. stronger and extended bass, vocals and more direct subdued and less clear treble
6. less stereophony
7. less analyticity
8. sound duller, with less contrast (dynamic)
9. the nature of the headphone reduces their dynamism and vibrancy present in K550
10. less mikrodetali
11. sound less engaging for the listener, profile more entertainment and consumer (mass), pleasant in reception
12. lower class technically sound (especially in the aspect of holography and fidelity)
13.  

 

[ianeith]

  Like kutizoltan83 said do NOT get the K551 the K550 are much better, i found this guide: https://tomigra.wordpress.com/2014/06/11/akg-k551-vs-k550-porownanie/comment-page-1/#comment-297
 
I do recommend checking out that guide but in case you don't want to read i copied this from the guide.
 
Characteristics of K550 compared to K551:

1. greater holography (three-dimensional)
2. larger scene from more distant from the listener audio presentation
3. more authentic, rich, resonant sound with a tangible and diverse sound
4. more dynamic / contrast (differences sound)
5. though more natural vocals withdrawn
6. brighter and more analytical
7. faster and more precise bass with more readable and more luminous structure sopranos
8. more air and freedom in the sound
9. holography and stereophony greater results in better readability tracks, instruments and separation (the details are more exposed)
10. more mikrodetali
11. sound more engaging, audiophile-profile, more analytical and tiring
12. higher class technically sound (especially in the aspect of holography and fidelity)

 
Characteristic of K551 compared to K550:

1. less three-dimensional sound
2. more concentrated closer to the scene of the listener's audio presentation
3. noticeable reduction in the depth of the scene and the flattening of the audio presentation
4. more dark and uniform sound, without distinction at the margins as in K550
5. stronger and extended bass, vocals and more direct subdued and less clear treble
6. less stereophony
7. less analyticity
8. sound duller, with less contrast (dynamic)
9. the nature of the headphone reduces their dynamism and vibrancy present in K550
10. less mikrodetali
11. sound less engaging for the listener, profile more entertainment and consumer (mass), pleasant in reception
12. lower class technically sound (especially in the aspect of holography and fidelity)
13.  

 
This is not an accurate account of these two headphones (actually an almost comical account thereof - "nature of headphone reduces dynamism and vibrancy..." What), so I would urge would-be buyers to simply go out and try them all, rather than decree a prevention of purchase for the K551 model.
 
The major differences between the two headphones stem from the cables used, which essentially means the differences are negligible; especially for most Head-Fiers.
 
K551s have a treble spike; if you like that in your headphones' sound signature then dig further. If you don't, look elsewhere.

 

[money4me247]

  This is not an accurate account of these two headphones (actually an almost comical account thereof - "nature of headphone reduces dynamism and vibrancy..." What), so I would urge would-be buyers to simply go out and try them all, rather than decree a prevention of purchase for the K551 model.
 
The major differences between the two headphones stem from the cables used, which essentially means the differences are negligible; especially for most Head-Fiers.
 
K551s have a treble spike; if you like that in your headphones' sound signature then dig further. If you don't, look elsewhere.

 
from my personal auditions (side-by-side direct-comparisons), i've personally found the two have negligible sonic differences. ymmv.
 
I do feel that how the akg k550/k551 sound depends on how well they seal onto your individual head. if they don't seal well, you lose the bass response. the k550 is one of my old favorite headphones though. recommend trying them out, especially since their price point  is hitting the sub-$150 mark nowadays if you are looking for an inexpensive pair of non-portable closed headphones.

 

[ianeith]

   
from my personal auditions (side-by-side direct-comparisons), i've personally found the two have negligible sonic differences. ymmv.
 
I do feel that how the akg k550/k551 sound depends on how well they seal onto your individual head. if they don't seal well, you lose the bass response. the k550 is one of my old favorite headphones though. recommend trying them out, especially since their price point  is hitting the sub-$150 mark nowadays if you are looking for an inexpensive pair of non-portable closed headphones.

 
Problem with the K551 is the flimsy, thin, short cable and the ultra-fat jack at the cable's end. I'm seriously considering getting them professionally re-cabled. All that aside, the sound is great; very detailed and fast (though not Beyer fast), and comparable to AKG's open models, e.g.: K702.
 
Moreover, I bought my K551s back-in-the-day when they cost upwards of $300, and still appreciate them at that price point. The low price today makes them a great buy; albeit faced with greater market saturation when it comes to the competition. Having said that, we still see headphones like the K553 for sale on Massdrop these days, and it would take a lot to convince me that the differences could be great there, as well (cables aside), further reinforcing the status of all K55x models as good buys at the sub-$200 price-tier (again, accounting for sound sig. preference).

 

[RockStar2005]

Here's a great custom EQ for Poweramp for use on the K55X series, esp K551.