Hey, i discovered a new technique recently. It can be useful to make some base material for cannons and blasts. In brief, you can make an syntesized explosion out of any impact sound.
Here are some examples.
1) take a sound with a clear impact.
2) make a copy, reverse it, unite with a previous sound - now you have a "whoosh" with soild middle part.
3) process this "whoosh" with a pitch, the envelope should look like this:
Very fast attack, starting from the lowest point going up and then medium decay and slow release. About 48 semitones should be enough.
4) add some fuzz or distortion, equalize the low end, raise some high middle frequency. Some reverberation may be good too.
The resulting sound isn't very suitable for solo use, but you can mix it with actual blasts and explosions to get a fat and lush sound effect.