Basics about music-listening diversity

I like to have a diverse experience listening to music. Thanks to last.fm (a.k.a. audioscrobbler) and some of my own database programming, I can measure both the actual diversity of what I've heard, and the impact on diversity each new piece of music would have. It's not really as simple as "measuring diversity". What is a diversity measure? Am I looking at the diversity of all the music I've heard, or only in the last week?

I track several different sets of "music I've listened to recently" and measure the diversity of each one. These are the diversity of artists and of tracks; by how many tracks I've heard and by how much time; and by time periods starting with the last week, the last two weeks, etc. up to the last year, and for all time. This gives 216 different snapshots of my recent music listening experience, which I add together to get one big measure of diversity.

For a diversity measure, I use the Shannon index. This takes into account both the richness (number of different artists or tracks) and the evenness (whether all the artists are represented evenly or with some more prevalent than others).