Music on stereo: The best Bluetooth audio adapters

It's all very simple: Bluetooth receivers transfer music from smartphones to old stereo systems. The small devices connect wirelessly to modern music players such as mobile phones and MP3 players via short-range radio and then forward their songs to the stereo system via cable. Our test shows that even the most technophobic can use these little helpers and that the receivers do not cost much. But they also have disadvantages.