[Jack & Rose] Background Music
To activate built-in background music feature on Jack & Rose, please navigate to Appearance > Customize > Background Music. You can choose whether to use 3rd party online streaming services like Youtube / Soundcloud, or upload your own mp3 file into the site (takes more bandwidth to your hosting plan).
Using Soundy Background Music plugin
If you want more customizations, please use 3rd party plugin: Soundy Background Music which is free and pretty easy to use.