If you really are serious about squeezing out the absolute max per dollar, this will be a lot of work, but I highly recommend studying mahgister. Where most of the work comes in, a lot of what he does will look to be honest rather kooky. But this is where you have to really study and learn your stuff. For example, what looks like empty old gas cans with soda straws coming out are helmholtz resonators. A helmholtz resonator is really any container (volume) of air with a restrictive passage leading in and out. Air pressure in the room flows through the passage into the container and back out again, losing energy in the process. The volume inside, together with the diameter and length of the passage, determines the frequency of sound that is most efficiently absorbed.
Most people just buy these things and so never do understand what is going on. The design can be worked out mathematically, but then you have to know what frequency you want to tune, and work through the math. Or you can do the whole thing by ear, or start with a ballpark math estimate and fine tune by ear. Or use existing product designs as a starting point and creatively build and tune your own.
This is just one example. His room and posts are chock full of them. Like I said, a lot of work. But for someone with plenty of time and willing to do the work I think you will be surprised how far these kinds of things can take you.
Most people just buy these things and so never do understand what is going on. The design can be worked out mathematically, but then you have to know what frequency you want to tune, and work through the math. Or you can do the whole thing by ear, or start with a ballpark math estimate and fine tune by ear. Or use existing product designs as a starting point and creatively build and tune your own.
This is just one example. His room and posts are chock full of them. Like I said, a lot of work. But for someone with plenty of time and willing to do the work I think you will be surprised how far these kinds of things can take you.