Biggest audio hoaxes

Anything claiming to use the principles of Quantum Physics to make their products better. Some cable manufacturers in particular but other dubious products a well. The experiments involved to show how QP interacts in the non quantum realm  is so esoteric & difficult to manifest it cannot be overstated. This was happening well before say Quantum computing was being researched, which has no timeline for being practicable on any definable horizon. Yes, it's true the transistor was completely the result of QP principles leveraged but the odds of anyone stumbling onto anything else that does so & w/o the government research budgets the transistor had do not rise to the level of being infinitesimal. Thee are perhaps good products claiming QP is a factor but they clearly have no idea what they're talking about or are just embracing their own cynicism in lying about it.

And the winner is-
muvluv! For having the longest run on sentences of the thread.
Although I am afraid you must relinquish your crown for the below or have one heck of a dandy run on sentence to explain:

for gold carries signal better than copper. Another one is amplifiers that put out low watts for thousands of dollars again this is just another placebo effect

While there are sound differences that we do not know how or of what to measure, there are marketers who take advantage of "A little knowledge is a dangerous thing." One example is the issue of skin effect attenuating treble through speaker cables. It is true skin effect diminishes the effective cross sectional area of a conductor by driving high frequency AC towards the surface of the cable. The question is how much does it attenuate high frequencies. At 20 kHz the skin depth of copper is 0.47 mm; at this depth the current density is diminished by a factor of e. For solid 8 gauge copper wire a pair of 5 foot lengths of speaker cable has a DC resistance of 0.0064 Ohms. The skin effect cross sectional area can be closely approximated by multiplying the skin depth by the circumference of the wire. This increases the effective resistance to 0.011 Ohms. put this in series with a 4 Ohm speaker and 0.5 Ohms for the output transformer windings. Take the ratio of the resistance at 20 kHz for the full circuit to DC resistance and you get a figure of 0.99896. Keep in mind the thinner wires in the transformer and the speaker coils have a diameter much less than the skin depth making their difference inconsequential. The 0.99896 ratio works out to about 0.0009 db at a frequency no adult can hear.
When a cable manufacturer does litz or ribbon construction of cables and charges hundreds of dollars with the claim skin effect is a problem it has to be fraud and fraud is how many merchants who feel they need to do whatever it takes to maximize revenue or perish, that should be enough to assume many other explanations for special care such as doing something about copper grain boundaries acting like little semiconductor junctions which have threshold voltages that intermittently start and stop conducting when cheap antenna cable has no difficulty conducting micro-Volts are disprovable junk physics. The justification for this kind of behavior is "Let the buyer beware." but it is not reasonable to require every audiophile to have a PhD in physics (even though many pop culture simulacra who calumniate "PhD stands for piled higher and deeper" seem to deserve to be taken for their contempt for everything too intellectual for them.
I applied to work as a sales consultant in a franchise store selling audio and video equipment. The store holds classes to educate the sales people on the latest audio and video products. It turns out that one cable manufacturer that advertises itself as correcting the skin effect problem teaches the sales staff to lie to the customers about skin effect. They have a policy never to hire a trained physicist who might break out the graduate school texts and embarrass them. If the staff do not know they are practicing dishonesty there will be no problem. If the customer is happy because he experiences placebo effect after spending hundreds or even thousands of dollars on such cables the rationalization is no harm is done.
But to me the customer's human dignity has to come first; everyone deserves the truth. What I see can be the downfall of the high end audio industry one day. You can't get away with deception forever because it is only a matter to time before t catches up. That is why I design and build most of my own gear. There are a few manufacturers I know who are honest and earn their profit and living. I only hope they are not hurt when the $20,000 power cords and $27,000 speaker cables are exposed and things come crashing down.

I was just saying the other day that people don't use the words simulacra and calumniate enough...