I made an explosion sound making program one time. It works by shaping white noise. I really don't know what I'm doing with DSP though, so the results are not what you'd call high quality. Anyway, it's here:
https://github.com/smcameron/explodomaticaHere are some sounds I made with it:
https://freesound.org/people/smcameron/sounds/51428/https://freesound.org/people/smcameron/sounds/51464/https://freesound.org/people/smcameron/sounds/51497/https://freesound.org/people/smcameron/sounds/51463/https://freesound.org/people/smcameron/sounds/51429/https://freesound.org/people/smcameron/sounds/51427/It's possible some of those sounds were made by hand in audacity by shaping white noise before I made my program to more or less automatically do what I was doing by hand in audacity, and I might have done further post-processing one the basic explosion noise that came out of explodomatica. The basic idea is you make some white noise, you taper it off in volume, and as time passes, you e.q. out higher frequencies, so by the end, only low frequencies are playing. That is, you kind of apply a sliding low pass filter, with the cutoff frequency starting off high and quickly sliding down to lower frequencies as time passes. Also, you might make two (or more) explosions offset in time, the first one being the "ka" and the second one being the "boom" in "ka-boom", with the first one having higher initial cutoff frequency (or vice versa? I can't remember) and the first "ka" being quieter than the 2nd "boom". Of course maybe add reverb if you want. You can add secondary effects like falling debris / dust at the end, but that's really out of the scope of the "basic" explosion noise. This technique is very basic though, and it sounds that way.