Rogue One introduced the idea of Kyber Crystals in the Star Wars movie Canon.
In the 1977 movie A New Hope - we see Obi-Wan Kenobi and Darth Vader battle with lightsabers and the blades repel with a 'clashing' sound.
Also in the 1977 movie A New Hope, they introduce the Death Star. According to Rogue One the laser in this was also built using Kyber Crystals. We see in this the laser beams coming together to combine into one large beam:
My question is: Why do lasers from Kyber crystals in light-sabers repel noisily but lasers from Kyber crystals in the Death Star combine?