I have just received a pair of Sennheiser pxc450 headphones. The sound quality is excellent, and it does muffle a certain amount of external sound. There is one thing I'm a bit unsure about. When I use the phones with my ipod I have to put the ipod volume up to maximum to have the volume control on the phones working properly. If I have the volume at half way on the ipod for example, I have to turn the volume on the phones up to maximum, and even then it doesn't sound lound enough. However, when I use the headphones with my hifi, on a low volume on the hifi, I only need to turn the headphones up a little. Is this normal, or do I have a fault in the phones? I have tried three ipods and they all have the same problem. This wasn't the case with the bose quietcomforts I tried at the airport. Thanks for your help.