You at least need 2 android phones and you can connect your devices in 2 easy steps

1. one phone should "Create Music Group".
2. another phone should click on "Join Music Group" and the app automatically connects for you to the "create music group".

* Up to 3 phones can join.

Now you can select a song displayed in the app and when you click on play it play's on all the connected phones simultaneously giving you a loud music.