The big/thick bass traps can help some, but they still do not absorb much down low (such as 50-60hz). Also, since they are broadband, they will tend to suck the life out of the room if too many are implemented. I have actually found that Owens 703 FRK panels work very well down to about 85 hz. And they are not huge (only 2 " thick). Very light. The have a metal foil that covers the front surface and acts like a tuned-membrane bass trap, but still reflects the upper mids/highs. The foil resonates with the bass frequencies and the fiberglass behind it will absorb that resonate energy. You just have to be careful not to put too many in your room because it can start getting to bright/harsh. They are excellent for handling the upper bass and midbass.
Tuned membrane bass traps or limp mass bass traps are the only ones that I have found effective for lower frequencies. I tried a variation of helmholtz resonators and it was a pain and didn't do anything. I didn't do the 6" / 15foot design, though.
You can build your own tuned membrane (but don't use dense panels for the inside):
https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/743040-tims-limp-mass-bass-absorbers.html Or you can get GIK's version, which are the Scopus bass traps.
I have also tried the GIK bass traps with the FlexRange limiter. They are okay, but don't work as well as the 703 FRK panels. The FlexRange limiter is really just a 1/8" piece of cheap wood that is loosely held in front of the acoustic material.