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I'm audio engineer by trade: these are not for sound proofing. It is a specific term and it links to preventing noise leaking from one space to another. That means airtight separation of spaces, structural changes, isolation, damping and so on.
At best, one can call these acoustic treatments. They belong to diffusion category as there is no dampening happening without mass. And for diffusion, we also need stiffness and mass, which these also lack. So.. Trust me mate, these don't do what you think they do; everything below 250Hz will blow right thru these but what you can get is diffusion at higher frequencies. You need to add mass and rigidity. You can think of filling the insides with cement, epoxy, plaster etc. to make them really effective and linear across the frequency bands, just as long as the plastic shell is really bonded with the filler to remove all rattle and resonances from the shell (tip: print "hooks" or internal truss structure to really bond with the filler). In the condition presented in the pics, they won't do much and will not treat all audible frequencies the same.
Plus: PLA is VERY resonant so most likely you have just created hollow echo chambers on your walls that sing at particular frequency... Acoustics is like black magic but remember: it needs mass or otherwise the very powerful low frequencies are blowing right thru while weaker energy high frequencies are refracted and reflected.. think what that will do to the overall sound.. i think you can figure out why these don't work and how to make them work (or forget it until you have studied this more..)
Designing any kind of acoustic treatment without some measurement equipment is like building a house while blind. Measurement mics are not expensive, there is no excuse of getting one. Almost with the price of one roll of medium quality PLA is what it takes, 110$ will get you a good one but the way those mics work, means they can be made for about 5 bucks (omnidirectional mics are more linear...).
You need to measure the room before and after and the mic can not move between tests a SINGLE millimeter, nor can it turn a single degree.. The better positional accuracy of the measurement mic you can get, the more accurate measurement is going to be for higher frequencies and these kind of flimsy things will be in the ranges where our measurements need PRECISION. The effect is expected to be very, very tiny and it is non linear and it is in the high frequency phase, almost the worst kind of data needed.. You ears most likely can't even pick up a difference or what you hear is caused by expectation bias.
Laws of physics don't care about bias and those say: you can't print flimsy sheets of plastic and expect them to work like your wall does. You need mass and rigidity that is closer to 1 inch of cement, 2 inch of wood or MDF and so on..