Yes, you can Double Up two ROLL speakers without using the app. Here’s how:
Connect to the first ROLL and turn on the second one.
On the first, press both the Volume “+” and the Bluetooth connection button at the same time. You should hear a tone that confirms the speaker is ready to Double Up.
On the second speaker, press the Bluetooth button twice. You should hear a tone confirming that it is trying to Double Up then another when the connection is successful.