I think this is a very interesting and useful experiment. It seems like you have done your research and that your methods should work well. Just make sure to try and keep other variables that may affect the data as low as possible. For example, make sure the person is at resting heart rate each time before you have the subject listen to a new kind of music. Also, maybe you could ask them if they've been stressed lately, or something to see if there is a reason why their heart rate is different.