song playing on the speakerphone and on headphone at the same time

Question

I'm using this code to select a song :

Intent intent = new Intent(Intent.ACTION_GET_CONTENT); intent.setType("audio/*"); activity.startActivityForResult(Intent.createChooser(intent, "Select a song"),1);

but when I'm using a headphone, if I select a song, it plays both on the speakerphone and on the headphone...

so, how do I set correctly the sound output, in this case?

thanks!!