If you don't hear any sound coming from the built-in speaker of your Nebula Cosmos or Cosmos Max, try the following steps: 

1. Turn up the volume on your Cosmos or Cosmos Max and play different videos in multiple streaming apps;
2. Update your Cosmos or Cosmos Max to the latest firmware by going to Settings > Device Preferences > About > System Update;
3. Switch your Cosmos or Cosmos Max to Bluetooth Speaker Mode (refer to How to Use a Cosmos / Cosmos Max as a Bluetooth Speaker ). Then, connect your phone to your projector to play music and listen to see if you hear sound;
4. When your Nebula Cosmos or Cosmos Max is in Projector Mode, connect your projector to a Bluetooth speaker or headphones via Settings > Remotes & Accessories > Add Accessories to test the sound;
5. Reset your Cosmos or Cosmos Max by selecting Settings > Device Preferences > Reset and try the built-in speaker again.

If you are still encountering an issue with the built-in speaker, contact us with the following information so we can help you find a solution faster:

1. Your projector's current firmware version by going to Settings > Device Preferences > About > Firmware Version;
2. A short video that shows no sound coming from your built-in speaker in both Projector Mode and Bluetooth Speaker Mode.