It took the Danish band Between Music 10 years of research to put on their first underwater concert in 2016. Before that, they carried out countless experiments, consulted with deep-sea divers and scientists, and even created custom-made instruments. The musicians say there are a lot of challenges of performing underwater. To start with, most traditional instruments don’t work, because the water dampens vibrations very quickly. In addition, it’s also important to figure out exactly where to place the instruments, because even a difference of 10cm can change they way it sounds. Musicians had to meticulously measure out the position for every instrument. Singing is difficult too, because singers need to learn to control the air bubbles created by their breath. The band has done 36 concerts in seven countries since its premiere in 2016. Between Music is now touring around the world. Next stop is Hong Kong in October. The video above shows what the concerts are like and what the musicians have learned about playing underwater.