I got my pair of PXC300s in the mail today. These headphones do what they claim: They knock out most all low-frequency sound in the ambient environment. When I first put them on in the kitchen, with the fridge, a/c, and fan going it was like inserting earplugs into my ear canals. Deep silence descended. Higher frequency sounds such as the human voice are definitely muted, but will still be heard.As for sound quality, it is a real pleasure listening to music on my laptop or Ipod. Good bass-, mid- and high-range response. Yes, the in-line battery holder is large, but it rests easily on the table, lap or pocket. Good for the office, train or airplane, but I wouldn't necessarily want to go jogging with them. Overall, a good set of headphones for the money.