I already used carbon based shungite from Russia with copper and quartz all along my electrical line...For many years at low cost...I am proud to say that this is my own homade experiments...
I dont pretend my "golden plates" best this product at all, i dont know, but at least is less expansive and work for me...
i had no problem with this company synergistic products at all but the boss treat me like shit when i wanted to discuss in one of his seller thread...i was menacing his trade it seems in his head...I like to discuss unlike this guy....
And anyway my acoustic method is superior to any electronic equalisation or electronic tuning... AT NO COST...
By the way i dont think coal will be usefull...But any minerals , any of them affect the S.Q. put on some point near the audio system but often negatively ... People are too lazy to experiment and prefer to throw money ....
Myself i already know that nothing best acoustic anyway even tweaks that work well and which i created or replicate...like my Shuman generators grid...
Why does that interacting with the EM field make for better sound? Because it can? Also carbon fiber cannot cost much so one would expect price to reflect that. One might try a lump of coal or two and see what happens. Inexpensive if it works so you can add as much as you want cost effectively. @mahgister could probably advise well regarding what materials work best and most cost effectively.