They certainly do make a huge difference.
In our older house I was using a TT with two subs,I could turn it up a bit,and then I would get feedback thru the subs.
I tried out four tri's stacked in the front:whualla,no more feedback and I could turn the system up as loud as I wanted.The bottom end was alot more defined and controlled,tighter ect.
In the newer house I have three corners stacked and 242's @reflections and more tri's up around the wallceiling corners(two more on the way and then my bass trapping should be done

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Two monsters on the back wall.
Now I'm thinking of diffusion just in front of the backwall.
I thought maybe realtraps diffusors(with bass trapping already there or SRL's prime 37 diffusor with my monster traps.Still thinking about it

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So far Gik has transformed both my rooms and it is a major system upgrade for cheap.
I've never heard a cable that can do what room treatments can do and have had the likes of Shunyata Anaconda helixes thruout plus Lessloss DFPC's.
Even just bass trapping makes a major change,we'll worth the price where cables you are throwing your money away when you spend 500-1400 for a PC,1400 would buy a quite a few bass traps and the sound is not suttle,
cables:I think I hear,I'll listen harder and then I'll hear it,traps you definately HEAR

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I still use my 12 Lessloss PC's as I sold off all my Shunyatas and made quite a bit of it back.
Totally Satisfied