The optimal distance for Bluetooth stereo devices of any brand is between 0.5-1 meter from the music device (e.g., your phone) to your headphones or speaker. This will help avoid signal dropouts.
Note that the quality of the Bluetooth signal can also be affected/weakened by obstacles such as walls, furniture, thick clothing/textiles, phone cases, or metal. Please refer to the individual product for further information on its Bluetooth range.