[Crazykiwi]

I love Grados and own a pair of 60's and 225's with a Fiio E17 DAC/AMP.  I had heard that there was much more to hear in the world of headphones so I kept researching for a pair of closed headphones  I liked the ideas posted around on Head-Fi about headphones with lots of "detail retrieval" and a "big sound stage."  When I looked around for this I found the AKG K550's and they were right on the money in those two areas and sound great. 
 
 
However, the overall sound to me feels hollow and thin on most recordings (Jazz, classical, vocal, rock) when compared with the Grados.  Most tracks sound like they are echoing from the bottom of a well.  After long sessions my ears adjust a little and I become slightly more content but when I switch back to the Grados I start to curse the AKG's sound again.
 
I had what I think may have been a similar issues with the Audio Tecnica AT50's but have only heard them once.  However a pair of closed MDR-V55 of my wifes sound a little less hollow.  My concern is that either most closed headphones sound this way...  or the flat frequency response is not to my taste.  Any thoughts on what the issue(s) may be?  Any suggestions on what attributes I should be looking for in a new pair of closed headphones?
 
I have heard and enjoy:
Grado 60, 225
Sennheiser HD558
AKG Q701
Denon AH-D600 (closed but not hollow sounding to me)
 
Thank You!

 

[ProtegeManiac]

  However, the overall sound to me feels hollow and thin on most recordings (Jazz, classical, vocal, rock) when compared with the Grados.  Most tracks sound like they are echoing from the bottom of a well.  After long sessions my ears adjust a little and I become slightly more content but when I switch back to the Grados I start to curse the AKG's sound again.

 
The K550 sounds like that on my mobile phone. Even on my desktop HPamp-DAC it can sound like that if I don't tighten the headband. It's easy to assume it must be worn in such a way that it barely feels like it's on your head, but it needs a bit of compression on the earpads. Some people have smaller domes and bend the headband (search for it here), but for me the sound improves enough with just wearing it at roughly three to four lines out (the markers on the metal part of the headband).
 
That said there's still a hint of that hollow sound, and a buddy over here took his apart and tweaked the dampening material in it (like how some speakers made of MDF that isn't dense or think enough benefit from having a bit more stuffing in them). I don't recall exactly what he used, but such a mod is likely somewhere in the mods thread. Note though that while the K550 is a great buy for the price, it's kind of in the same sense as it is with those closed Fostex cans that just sound god awful out of the box and will totally need a lot of tweaking, particularly with the dampening. The K550 needs a bit less of that  but it still does. If I were looking for a closed headphone I would still buy the K550 (or a used one, so I get it cheap and not feel bad about taking it apart) over the MDR-1R - I like the sound of the latter out of the box, even with my smartphone, but the cups are just too small that I don't like the fit around my earlobes. I almost did buy the K550, but I came across a pair of ASG-1 IEMs and got those instead. Paid half the price I would have paid for a new pair of K550s, easier to lug around and drive out of a smartphone, and they don't rely on the tips as much as anchors in my ear canals (and don't itch like other IEMs).
 
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I had what I think may have been a similar issues with the Audio Tecnica AT50's but have only heard them once.  However a pair of closed MDR-V55 of my wifes sound a little less hollow.  My concern is that either most closed headphones sound this way...  or the flat frequency response is not to my taste.  Any thoughts on what the issue(s) may be?  Any suggestions on what attributes I should be looking for in a new pair of closed headphones?

 
Closed headphones tend to have a lot more bass because the isolation is better, but chances are they also introduce cancellation in the midrange and even the treble, hence the improvements to the K550 and those Fostex cans when properly dampened. If you don't need closed headphones you really don't need to worry about those, but if you do, then I'd suggest reading up on the K550 modifications and see what you're comfortable with doing on your pair.
 
Note though that even the modded K550 I've heard doesn't sound as "full" as Grados' tone, but what's great about it is you get a circumaural earpad that is more comfortable, with drivers farther from your ears that don'tresult in Grado's trident-shaped soundstage (strong L-C-R, notes between L-C and C-R sound like they're coming from behind; drums are in confusing positions, though tonally very satisfying).

 

[Crazykiwi]

Thanks for the detailed reply.  I may try some of those mods since I do really need a pair of closed headphones for traveling.

 

[ProtegeManiac]

Found a detailed modfication log for a K551 (AFAIK it's the same headphone but witha shorter remote cable, and colors that  presumably would better match your phone, like a white one for a white Galaxy S or iPhone, or that and a two-tone black silver to match silver and black phones like HTCs and iPhones). Note that the points he didn't like might actually work in your favor. In any case the great thing is it has measurements to back up each modification, although some of them are too complex (like his building a notch filter). Looking at the stock graphs though and his final output, I think the plasticky and hollow-sounding upper midrange and treble can be explained by that peak in the treble smack next to a trench in the upper midrange.
 
http://www.mediafire.com/view/pzbaqy8nuek1kkq/AKG%20K551%20modifications.pdf

 

[Crazykiwi]

Thank you.  I will go over those mods and consider them.