Real life distant artillery/mortar explosion sound is very powerful and terrifying. In the game, the sound is not related to the real explosion sound, and is not hearable far enough. The real sound is a distinct two-part ripping thud that is different from other explosions. Getting this sound would make the game world more frightening and realistic. And therefore better!

Here's a bad quality version of the lovely real sound, it brings back memories <3 : http://www.sounddogs.com/sound-effects/2224/mp3/438044_SOUNDDOGS__ca.mp3