You would not imagine it, but doing just a few mods to the HD555 lifts it to an entirely new class of headphone. I have mine on right now and enjoy them as much as I do my DT880s, perhaps more than my m50s, although, obviously, they are so open now that m50s and these are apples and oranges. These things blast out sound for everyone else to hear, and the m50s when you let the pads press together go silent at ear shredding levels.
I really like the idea of an open Audio Technica like the AD700 (I think that is the open one, or maybe Ah-D700, don't remember, just know they are killer value for an open set of cans.)
But the mods aren't hard and don't forget to mass load the back of the drivers (be careful and be sure to never cover the hole in the center, or let anything fall in, I am sure you would ruin the driver that way). I used blu-tack, but some use dynamat, basically anything that can be cut or pressed to fit that evenly adds mass, because after the mod, the driver is practically floating. The 555 uses click locks on all it's stuff that doesn't use screws to hold down or in, This means, you end up with something very very close to the HD600 if you do it right, but can be powered on almost anything, and comfortable as one would expect the 555/595 to be. I think they are more comfey than my Beyers, but not by much. I have no preference, but the fact that I can use the DT880s as a reference point gives you an idea of how much these headphones change after the mod. It is instantly a new set of headphones that can hang with some big names. Frankly, I am really enjoying them. I had them in the closet for a couple years beacuse I felt they were boring. I finally got around to picking them apart and modding them since my Grados pissed me off, I wanted another project. I bought these almost ten years ago, and only now are they really making me re-think the sennheiser brand.
You already have them, so why not try, right?
If you need closed cans, there are a couple nice ones from AT, Beyer, and Shure, but I find the 440/840s to be harsh... way too harsh to be musical. My 440s are strictly for monitoring since they are lifeless ear shredders that give you everything, the good and the bad. They are built like a tank though. I just don't think they would do well on a portable. I have a hard enough time preserving my hearing using a proper amp as they just are so.... cold, not dark, mind you, just clinical, lacking character, and not making music very fun to listen to. Like I said, good monitoring phones, bad kick back and relax music phones.
I have been able to acheive very nice sound out of my sansa fuse from these phones I own: the HD555s modded that I speak so highly of (they also sound good amped, so they scale now, they didn't before, open phones that can move this much air... only a few can do it right.), The *real* Koss Porta Pro, there is a best buy version that uses a jankier driver, so look for the chrome on both sides; Audio Technica M50s, these guys have been universally praised here, so I need not to say much about them that has not already been said. They are one of the best closed back cans you can buy for 150 and under, possibly even more than, depending on what you like about them. Sony XB700s. A Guilty pleasure that also performs. These look like almost a joke, but no joke, the massive drivers can serve up a rather well balanced sound, extremely efficiently, with great isolation, and well controlled bass down to well below 20hz. The bass is there because they can do it. They don't make it a point to overdo it. They just provide what is being given. Most phones can't go that low so they are odd at first, but you will notice the smooth HF and holographic midrange. They are a good portable player set because they are so efficient. They are more than any other headphone I have. The massive driver membrane and the ear cavety from the huge pads creates this environment where you can enjoy techno as it was meant to be heard, from dance to IDM to electropop, but I find well recorded jazz and rock records sound amazing on them simply because they have the slam other phones lack from a portable. I generally keep the sansa in the bag for the xb700s. they just go together so well. I leave most of my other phones for work or home systems. I have tried my DT770s and 880s on the sansa. It wasn't bad on the 770s, but it wasn't anything to write home about, and the DT880s just were out of it's league.
A couple of AKG phones never worked on a portable either.
Mod your 555s or try the AD700s, I am thinking of buying a set, since I have decent closed back ATs, I want to hear their open sound.
