So I'm thinking of replacing the standard white earbuds that came with my iPod. I thought, "why not?" I was in A&B Sound yesterday looking at some different models by Panasonic and Sony. I'm willing to pay about $50 CAD (which I guess is like £50, when you think about it), and the models I am looking at are all pretty comparable to the "upgraded" iPod headphones (which are $50 at my work). I was looking on the back of the box for the Panasonics and it said that the top end of the frequency response was 25,000kHz ... So how can I somewhat objectively measure the sound quality of headphones that will reproduce sound way above the threshold of hearing? I want to be fairly scientific about how I choose my new headphones.