I'm not aware of many people owning the Koss UR-55, but I just did a mod the other day and I liked it so much that I felt I absolutely MUST share it with everyone. It turns a good headphone into something really great and improves many things.
I always liked the UR-55 but sometimes I felt the sound was very very slightly muffled, but still very good for the price. The sound was just not as crystal clear as my Maxell DHP-II or even the Beyer Dynamic DT-235. They do have more bass than both and are even more fun to listen to. They seem to have the Porta Pro sound signature in a way. I don't think it uses the same driver at all. The UR-55 driver appears to be 40mm. I don't think it's a titanium driver, because the sound is not as bright as the KSC75 to my ears. The highs are definitely rolled off and the sound signature is very non fatiguing.
Since my UR-55 wasn't being used as much I decided to try and open them up to experiment. I also wanted to figure out if they were really open, closed or semi-open.
The pads along the edges are held in place by adhesive behind some plastic. The adhesive of course doesn't cover up any holes. What you do is put a small thin flat screwdriver behind the plastic and gently lift up and work your way around. Once it's removed there is now three screws. I 100% suggest to DO NOT REMOVE the ear pads. If you do, be very, very careful. I was able to reuse mine after removal.
Once the screws are removed you will notice that the metal grill has thin fabric covering the back of it. The grill is held in place by bent small metal tabs. To remove the grill you can bend the tabs and press gently against the grill with screwdriver. I had to go back around to the outside and pry off the grill. Once it's off, there is very little chance it's going to be reusable!
Next, remove the fabric from the plastic. This takes a long time since it's glued in place in four areas. The fibers hold on and it's hard to get them off.
If you are going to remove the metal grill I suggest doing it WITHOUT removing the pads. This may be very difficult and I haven't tried it. You can pop off the Koss logo and use the hole to force it off. Just be careful to not poke the driver inside!!
When I played music from them after doing this mod the sound was quite impressive. The differences to my ears were not subtle. Have you ever done the Grado SR-60/80 mod? The result of doing this is even MORE noticeable.
I have a feeling that the driver of the UR-55 is similar to the driver of the SR-80 and needs air to sound it's best. I'm not sure of this, but I think this is the case.
The biggest change i've noticed is that the soundstage is much better and more noticeable. The overall sound is much more clear and I'm not sure how this could be. The highs are obviously still rolled off, but the mids SEEM to be even more forward. The bass seems to be reduced slightly, but not as bloated as it was previously in some bass heavy songs. Imaging is just amazing for a $50 headphone. Now this part is probably just my imagination, but it felt like there was even more detail than before. In one song, I even heard some recording hiss.
I did this mod at 3am and I was so impressed with the differences that I laid in my bed listening to all my music until 5:30am! No joke!! Despite the driver being a bit more open the sound doesn't leak out as much as my Grado SR-80 with the grill removed. It's strange that there is still some decent isolation.
I thought that maybe all these changes are my imagination, but I definitely don't think this is the case. I listened to them for another 3 hours today and i'm still impressed. This may also be a good budget solution for a portable open gaming headphone. I'm going to test them out later today.
Hopefully someone who likes doing mods and doesn't mind some risk can try this. The mods are 100% NOT reversible, so it is a risk and you most likely void the warranty! If you don't like the changes, you've wasted $50. I felt it was totally worth it in every way. It reminded me of when I did my Grado SR-80 mod. It felt like I had turned my $80 headphone into something much more expensive. I can't say it will be the same way with this, but the sound was really improved by a lot.
I've noticed that some low quality MP3s I have sound VERY bad on these. Even more so than a lot of my other headphones. They're not THAT revealing, but I kept wondering why some music sounded like garbage on these and it was my source file.
The best music for these that I have is Pearl Jam, Radiohead and Imogen Heap. If Imogen Heap doesn't "Wow" you on these headphones after the mod, I don't know if any under $75 headphone will. After lots of testing I don't think these need an amp, but do benefit from one.
Edited by tdockweiler - 11/20/10 at 2:06pm