Advice on desensitizing my dog to scary sounds without a loud speaker or way to replicate them?

One issue I have with my dog is he gets very scared (lots of shivering, heavy panting, fast heart rate, unresponsive) when there are a few certain sounds and unexpected noises. I've tried several things to desensitize him but I cant seem to comfort him with these.

3 sounds mainly that cause this. 1) Loud thunder 2) Snow/ice falling off my roof and hitting the wood deck 3) Fireworks. All 3 of these sounds I cant replicate in the normal way that I see suggested all the time, which is to play them on a speaker and increase volume. I dont have big speakers, and the speakers I do have are not loud enough or bass-y enough to produce that sound. He also can easily distinguish the sound is not coming from outside and he doesnt get scared of it when played on a speaker. Its also the surprise factor, all these sounds come suddenly and usually hes sleeping and resting then they just happen. I live alone and its very quiet in my house, so these sounds are very loud and surprising. Especially the snow falling from the roof. I have a high roof and it makes quite a loud bang when it lands, even I get a little shocked, so I feel bad for him because he has no clue whats happening.

I try to play with him and give treats and make the sounds positive when they happen but as soon as the first one happens he immediately starts shaking and is terrified. Then it is hard to get him out of that mode. He becomes somewhat unresponsive and is kinda in shut down mode. I also am surprised by the sounds and can't really predict when they will happen. The snow falling is the one that happens the most often and it just randomly happens. If I could predict it I could try to distract him or create a positive scenario when it happens but its just random, same with fireworks, sometimes there will be lots, sometimes none on the firework days. Ive tried an ear cover and a thunder shirt, neither worked.

Is there any way to desensitize him to these unexpected loud sounds without a speaker? How can I try to make them positive experiences? The snow falling from the roof I do have one idea that I think I can replicate. Im going to fill a ball with some water and I can throw it on my roof and let it fall on the deck. That will sound pretty similar to the snow falling. I can give him some treats/lick mat/bone and even have the door open to show him its not scary and I think that will help.