I don’t know much about the inline silencers, but I had a real noisy fan that I put inside of a tote that I lined with pillows and egg crate foam so I wouldn’t hear the fan anymore. Just had to cut a hole on each side for the ducting to go through
I ended up buying a more powerful fan and running it at lower speeds but the silencer was in service for a couple of years and was definitely better than nothing.
My grow cab has a long, foam filled exhaust muffler. It works really well. Reduces the noise by 2/3-3/4 when it is attached. Which is always unless I am cleaning pollen out of it after a seed run.
The actual inline blower fan itself is mounted inside the cab, so the cab itself is working like the tote with pillows described above.
I have a bookmark of a good looking project for this if ever needed, I like that this guy’s coming at it from a speaker/audio designer standpoint like building driver enclosures.
I’ll also say, @Papalag that if you’re switching fans in the future the AC Infinity Cloudline I got to replace a cheap Vivosun is so damn quiet, though I did size it up and use a larger fan than needed so it runs low. I think they’re probably the most silent option you can get outside maybe commercial grade stuff and even that IDK.