The range of Bluetooth depends entirely on the wireless environment around the speaker. In a moderately noisy Wi-Fi area, expect the range to be somewhere around 10 meters.
Please note that the range decreases significantly if the speaker and the audio source are separated by metal and concrete walls or floors/ceilings. For optimal playback stability, keep the two devices within a clear sightline.
Poor Bluetooth stability can also relate to the playing device itself. Always include a restart of your playing device (iPhone, Android phone, computer) - and the speaker - in your troubleshooting.