#15: The differences in the two frequency responses are not going to affect what you hear. Humans can only hear between 20Hz and 20 kHz (if you don't have any hearing damage) so the extended frequency responses may look nice on paper but don't produce better sound.

#19: These do a great job of keeping the sound in, so they'd work well for your purposes.

#15 it was just personal preference i guess. To me the HD555's sounded alot better but everyone has different tastes. The two are used with amps so the impedance is negligible. But the HD555's are open air while these HD-280's are not.
They both require break in periods so id try these out as long as you can before the return period is up to see if the sound matches the quality you want.

Are these good for larger heads?

I've had these cans for YEARS now, and they are still kickin sounding unreal. The top of them has broken a little bit, but they are still just as comfy to wear and I love them. Sennheiser rules.

my Sennheisers seem to squeeze my head too hard. i'm looking for replacements which i can use for longer than 30 minutes at a time.

I posted similar comments on an old sale of this stuff. Anything less than $100 for this set of headphones is a good price.

These do indeed keep the music in and the sound out. I've listened to some really loud drum corps; nobody could hear them that walked within a few feet of me. Great headphones.

Sennheiser makes one of the best headphones. I just wish these had noice cancelling built in.

Noise canceling? They cover the ear and with music or something playing (even not very loud) you can't hear anything around you. I love these things ... I paid $100 for mine and I'd do it again in a heartbeat.

Company makes amazing headphones, durable, clarity, and descent price.