Android : Android:where to save audio files for allowing user to dowload it if he wants

I am Developing an app for playing audio files (rhymes) . But to limit the size of the app i want to add a functionality of download button for the specific audio files. Idea is- I would provide them 10-15 pre-embedded audio and other audios can be downloaded if they want. But i don't know how to do it. Where to upload it. Or can it be Stored in some external database.which can be accessed by the user. I don't want to make the app size very large. Thanks