Well, this morning I had a chance to compare the HTF600's to the Koss UR55's side-by-side. But first, a few remarks about the Panny's...
I was out of town on a business trip all last week and hadn't listened to the Panny's for probably 10 straight days. While on the road, I enjoyed some music with my iPod and Etymotic Research ER-6i's, which on the whole I consider a fairly neutral IEM. I think they lean a little bright and bass shy, but both of those traits are just small variations from neutral. Many people used to exaggerated bass (anyone under the age of 30 ) find them bass weak. I have to say that when I listened to the HTF600's for the first time again when I got home, I was surprised that they weren't as treble recessed (dark) as I remembered. Now my daughter has been using them so I can't say if it's just my memory or more break-in time, but whatever the reason, these now sound quite good to me. They have the typical bass hump as I remembered which does bleed a little into the mids giving that slight muddy sound, but it is not as prominent as I remember, and with a lot of music (80's rock/pop, electronic), it isn't very noticeable and often adds weight to bass that is weak in the recording.
With the velour pads, I don't detect any difference in sound whatsoever. When installed, the holes in the back of the Beyer pads touch the plastic that surrounds the drivers - there is no air moving through these holes so forget about that.
OK, on with the comparison. The Koss UR55's out of the box sounded very much like I remember the HTF600's sounding after unboxing. Bass was bloated and muddy and treble was quite recessed - basically horrible sounding. I let them play continuously for the past 2 days and they have changed quite a bit now to the point I think they are ready for evaluation.
SOUND - they have the same basic signature as the Panny's. In fact, on casual A/B listening, I find it hard to tell the difference. Only when I repeat passages and focus carefully do the differences come out. The UR55's have a slightly larger bass hump which makes them hit a little harder and sound a little rounder in the mid-bass. With my jazz sample music, they sound more bloated than the Panny's. With 80's rock/pop (synth drums) and electronica, they just have more punch and slam. This added punch has a downside though. Since the mids of both phones seem almost identical to me, I think the slope from bass to mids is steeper on the UR55's, which results in the lower mids sounding a little thinner - not in a good way. Almost like there is a thin gap between them. It isn't very obvious, but to my ears, the Panny's sound a little smoother in transition from bass to mids. I think this is because the bass isn't boosted quite as high on the Panny's. The result is that with well recorded jazz and rock, the Panny's sound better - like neutral with a bass hump. On 80's rock/pop and electronic music, the UR55's sound better because the bass is more defined with a harder kick.
Treble with both phones is very close, which is to say just about neutral to my ears. If I had to find a difference, I would say the UR55 is a smidge brighter sounding, which I think also contributes to the impression of more definition in the bass (like turning up the sharpness control on your TV a little). Neither headphone will ever be mistaken for high-end. Neither benefits from an outboard amp - I couldn't detect any appreciable difference in sound quality between my amp and my iPod.
One important distinction between the Koss and Panasonic is comfort and quality. I find the UR55's somewhat uncomfortable after more than 30 minutes. They sit on parts of your ear and the pressure has me readjusting them occasionally to relieve pressure points. To Koss's credit, the UR55's are simpler and sturdily built and less likely to break than the Panny's, and since they have a shorter cord and the cups turn 90 degrees flat, they are better suited to tossing in a backpack and traveling. The Panny's on the other hand, surround the ear and feel quite comfortable. I actually think the pleather pads are softer now than when new, but really, for $18.50 the velour pads were a good buy - they transform the Panny's into an almost luxurious feeling headphone. The Panny's even look high end with the velour pads. However, the Panny's are definitely more fragile in build than the Koss's so I think they are more of a stay at home headphone.
In my opinion, grab the UR55's if you want a bass-heavy headphone to throw in your backpack and listen to when you're out and about. If you want an inexpensive bass-heavy headphone to keep at home and relax with, the HTF600 is a little more natural sounding and a lot more comfortable. If you listen to acoustic rock, jazz or classical music, look elsewhere.
Thanks for posting this comparison. I think I will just stay with my Pannys, RX700s and Ksc75s and not look any further. I do have a curiousity of the Koss ProDJ100 though..oh man this never gonna stop.....The HTF600s are sounding way better now especially when I boost the mids and highs. NICE!