Here is a link to a tool which is designed to train the ear for critical audio evaluation. It is one of the tools that we at Harman Automotive use to keep our ears tuned. The goal is to be able to determine slight dips and peaks at various frequencies. This is especially important in the automotive space where interior reflections and speaker placement are less than ideal. It could be very useful for you guys in evaluating headphones since your frequency responses are usually far from flat. No matter your opinion, at the very least, it's fun to play with.
http://seanolive.blogspot.com/2011/03/harman-how-to-listen-listener-training.html
