Helmholtz resonators and diffusers...(straws-bottle-plumbers tubes or cardboard one)
My wodden foldable screen for psycho-acoustic use...
Concrete block for damping speakers and springs....
Composite platforms...(Bamboo plate-sorbothane-granite plate-cork plate-quartz)
Shungite+copper+graphene all along electrical grid or connector or router or electrical box....
Modified grid of Shumann generators....
Ionizers....
Various minerals...
SPL meter....
All the rest are simple tools anybody own....
And various cheap materials for passive acoustic treatment including aluminum paper... Empty paper rolls for some resonators... 😊 You can laugh i will smile the last...