Download audio link - help!

I am defining a URL to an MP3 file and then having a button use getURL onPress to open it. On my computer, this opens a dialog box to save the file.

However, on some computers, it opens the file in Quicktime in browser.

I want the link to always go to the save dialog box, so that it doesn’t go away from my site, and so the user can download the file instead of just listening in browser.

Any ideas on how to do this?