cryogenically treating speaker cables. Back in around late '80's or early '90's cryoing rifle barrels was all the rage. Had one cryoed and it was 100 bucks pissed away. In spite of anecdotal evidence there is no proof that it does anything.
What’s your vote for the most ridiculous, overpriced, and useless tweak?
My vote: Furutech Outlet Cover 105 NCF $220, with “special crystalline material that has two “active” properties.” https://www.thecableco.com/outlet-cover-105-ncf.html