If anything, I would do the opposite. Playing the louder bass now will simply condition the young dog.
When I lived out in the country we had hunting dogs that pretty much weren't scare of anything. They were used to hearing gun shots, thunderstorms, tractors, etc. and it never phased them.
Yet when my mom opened the oven, they got scared and left the room. It's because my mom once had a small oven fire and when she opened the oven door it startled her quite a bit, which must have freaked out the dogs. Ever since that happened, whenever the oven door opened (even if it wasn't on), they got noticeably worried.
One of my lady friend's younger dogs is terrified of the thunder. But the older dog isn't and never was. I was around when the older one grew up and showed no signs of worry during storms. Younger dog grew up without me there all the time and when there's strong thunder clap my lady friend would jump.....scaring the younger dog that now fears it.
Be the Alpha Dog........CRANK IT UP
........and show no signs of fear!!!
Oh, and tie a bell to the back door that they can hit with their nose. Every time you take them out to do their thing, tap the bell, or hold the dog and make the dogs nose tap it. It doesn't take long at all before the dog rings that bell when it has to go out. My friends always got jealous of that!
"What's that bell ringing".....Ahh, the dog just has to go to outside.