Most rooms don’t need acoustical treatment.

@millercarbon - @jumia has not heard many power cords in even a middling quality audio system.  Sheesh.  Why are there so many posters who don't believe that cabling sounds significantly different?   Don't they have something better to do in their lives?

I moved from a 5500 cu.ft. listening room of good but not great construction (windows to the side and front walls, 5/8" drywall & 5/8" acoustic wall material) which reflected too much sound despite my 2 pairs of Hallographs and full array of SR HFTs.  My new home has a near SOTA listening room with built-in bass traps (16" thick multi-material acoustic walls w/4 chambered activated charcoal filters, 12" - 15" 3000 psi steel bar reinforced slab, etc).  No windows, doors the same construction.  I still require those Hallographs and SR products for the mids and highs with side and ceiling acoustic foam treatment.  My audio system is wonderful now, getting the most out of 30 year old Legacy Focus speakers.   Not needing to change electronics (other than DAC) for 15+ years.  Cabling upgrades when manufacturer has made a breakthrough.  This is not the typical audiophile or listener setup.  However, my living room has silk and cotton battened wall treatment on front and rear walls which alleviate one open side and one side with full french doors.  (Oh yes, 90 oz carpet in each room).  The sound of the $5K audio system is also excellent.   Going to audio shows is a crapshoot due to the awful acoustics.  If a system can sound great there, something in the that system must be great (or most of the components).   Only 4 rooms competed in my last audio show in L.A. 2017.

I considered Helmholtz resonators decades ago but purchased two pair of Hallographs supplemented by SR HFTs.  I agree with Mahgister.   My tuning is for music, not scientific measurements just as an anechoic chamber is made for testing, not music.

I dislike the use of DSP for acoustic corrections for speakers.   Some manufacturers feel that is the solution to mate their speakers to rooms.   I built my listening room to accommodate most speakers, especially those that reach deep bass (my cut-off is now 25 Hz).  My room isn't perfect but it is good in so many factors that I can concentrate on minor tweaks (or upgraded cables/equipment).  Lonemountain is correct-DSP won't make an adequate sounding room great sounding.