Bluetooth speakers tend to do best when they're within a range if 10m from the source device, but this only applies when there is a direct line of sight. In our tests, we have managed to get good clear reception from about that distance, though obstructions such as walls or doors affect this range substantially.

To maintain a stronger Bluetooth signal, try to keep the phone in the same room as the Bluetooth speakers. As long as you maintain line of sight, the audio shouldn't break up too much, even if you do happen to exceed the 10m distance.