There are many types of music which some authorities permit listening to during the Omer:
Rav Shlomo Zalman allows classical music and chazannus. (Halichas Shlomo)
The Chelkas Yakov allows recorded music. (1:62) I have also heard this in the name of Rav Hutner.
The Sefer Eleh Haim Moadai permits music while driving (where one cannot dance)
[my thanks to Rav Enkin for the sources]
I have seen these heterim quoted by many people and relied upon in many circles.
Do they also apply to the 3 weeks? What are the factors involved? Is the prohibition against listening to music more stringent during the three weeks than during the Omer?