These are Skywalker Sound sound effects consisting of 2 medium explosions. They debuted in Star Wars: Episode V - The Empire Strikes Back (1980) and were recorded by either Ben Burtt and/or Randy Thom. It seems to be considered as a stock sound effect though. Links: https://soundeffects.fandom.com/wiki/SKYWALKER,_EXPLOSION_-_BIG_CRUNCH#Audio_Samples