The headphones' rechargeable battery is not fully charged upon delivery. Before using the headphones for the first time, charge the rechargeable battery for a complete charging cycle without interruption (> Charging the headphones' rechargeable battery).
The Sennheiser Smart Control app allows you to use all functions and settings of the headphones and to e.g. adjust the sound to your liking using the equalizer (> Installing the Smart Control app).
Connect the headphones to your smartphone via Bluetooth (> Connecting the headphones to a Bluetooth device).
For good sound quality and best possible wearing comfort, the headband can be adjusted to properly fit your head (> Putting the headphones on and adjusting the headband ).