With manual action guns and appropriate cans, .300 blk subs are gonna be quieter.
With semi autos, though, there are a lot of moving parts in both the literal and figurative sense. Short recoil or delayed blowback tends to have less port noise than gas operated, and definitely less than simple blowback, but again, lots of variables in play.
My Marlin camp 45 is my only .45 ACP carbine, and the port noise is horrible with simple blowback and a light bolt. But I also don't find .300 blk particularly tolerable from an AR, even with gas adjusted. .45 pistols, again, host matters. My 1911s and 3rd gen S&W autos I can do with no ear pro just fine running my Phoenix M, but striker fired hosts tend to snap my ears. Same deal with 9mm, my S&W 3906 & 5906 and Beretta 92 being perfectly comfortable, Remington RP9 a little loud for my liking, and the blowback Stribog teetering on the very edge of what I can tolerate, all with the same can model and 147 or 158 gr subs. .380 out of my locked breech DB380 is pleasant, but very offensive from the blowback CZ83