Pros Durability, stereo/mono switch, independent volume control, cord is plenty long, killer passive noise reduction
Cons They are quite heavy
Summary I searched high and low for a good set of cans tuned to the mids because I do voice transcription. My QZ99's have exactly fit the bill for what I need. The passive noise isolation is outstanding. As the previous reviewer mentioned, they don't have much bass or treble, but they're not intended to have; they're tuned for voice. Even with a lifetime warranty, I'm most likely going to purchase at least one more set (maybe two) and hold them in reserve because they are that perfect for transcription use (and if/when they do short out, if I'm in the middle of working I'll need a spare).
"Built to last"on by fritzswiss
Pros Heavy duty mostly metal construction, volume control, and stereo/mono switch
Cons Not discreet, nerd factor is high.
Summary I have had the Koss PRO 4AA and these QZ99. Both will last decades!
Pros Solid, durable design, Affordable, coiled-cord, single-entry cord, super noise reduction, Koss lifetime warranty.
Cons Heavy, muddy bass sounds, distort quickly.
Summary I bought these to replace a pair of UR30's that stopped working. For my purpose these headphones work; I play the drumset in a band and use headphones as my monitor since the noise reduction decreases the volume of the drumset. My UR30's worked great for this and I plan to send my UR30s to Koss for repair under their lifetime warranty. My UR30s worked great for several applications, from my Roland Stage Piano, to my drumset monitor, to my mp3 player, and more. The QZ99s not so much. I plugged the qz99s into my mp3 player and was instantly disapointed at the lack of bass. When I increased the bass on the mp3 players EQ all I got was a real muddy response. As I continued to tweak the EQ and increase the bass I quickly reached the point at which these headphone began to crackle and distort. Extremely disappointing. I put on a pair of Sony clip on headphones using the same bass settings and no distortion whatsoever. Clearly Koss missed the mark with the QZ99s.