I thought I would compile a more or less complete list of woo/ flim flam / snake oil, a handy reference so when you find yourself in a Hi-Fi retailer and the assistant mentions one of them you can turn smartly on your heel and walk out.
HI-Fi just will not work without electricity, so let us start there.
The mains plug, this needs to comply with your local electrical regulations
thats it, nothing clad in carbon required, just a proper plug that wont endanger your family's lives.
Fuses obviously complete woo, and if you have even considered them you need to give yourself a stiff talking to.
Mains cable, again has to be certified for local electrical regulations , but that is it safety is the only consideration, a fancy mains cable cannot make an iota of difference to SQ.
Cable lifters, please...
Grounding boxes ,( poorly made yet expensive box filled with cat letter) a particular favourite of mine, considered by many to be the absolute zenith of snake oil.
Grounding through your house's electrical circuit, again safety first, copper rods in the garden and persuading the cat to wee on them forget it.
I am going to group together all the really truly ridiculous nonsense, dots, wooden tuning discs, wiggly wooden rods, crystals, bits of bent plastic that fit in between the plug and the mains block,( a shop actually sells these, not only useless but potentially lethal) little bells that you stick on the wall, anything with 'quantum' in the title.
Cables should be fit for purpose, they should be of the correct gauge ( thickness) if they are interconnects they should be of the correct impedance for their purpose.
They should be robust and properly constructed with strain relief and properly engineered connectors. Thankfully 'Pro' audio cables fulfil all of the above and are not expensive.
Mogami, Van Damme both excellent and made for the job.
Cables if their electrical parameters LCR ( inductance, capacitance resistance ) vary hugely from the norm can alter the loudspeakers frequency response, take note this isn't an 'improvement' just a very crude tone control.
USB cables again just get a cable which has been certified by USB.org it will have a little flag attached, a more expensive cable will not make the slightest difference to sound quality so save your money.
Expensive ethernet switches, the enterprising snake oil manufacturer never sits still when there is always someone out there to fleece.
Linear Power Supplies:-
The rise of the linear power supply, which has lined many a dealers pocket, essentially preys on the neurosis of the audiophile and is fed by magazines, retailers and of course the people who make them.
I often hear that a linear power supply has 'x' less noise than a SMPS which may or not be true many designers preferring to use SMPS ( switch mode power supplies) because they are quieter, but of course we do not listen to the power supply we listen to the output of the device being powered by the supply.
Electrical component are plugged into the AC (alternating current) mains and that AC is converted into DC ( direct current) filtered, regulated and smoothed by the device.
In any properly designed component there will be no evidence of power supply noise on the components output, which means that a 'boutique' power supply ( I saw one the other day that cost £8k !) will not make the slightest difference.
Over at ASR ( Audio Science Review ), Amir has measured hundreds of electrical components and only a very tiny percentage show power supply noise on the components output, which means that they are just particularly poorly designed'
Their internal power supply regulation and filtration has allowed power supply derived noise through to the very output of the device, they are very much in the minority and why would one buy such a poorly designed device in the first instance?
Turntables may benefit from isolation because they are essentially seismographs, placing on a wall works well isolating the TT from foot fall, of course even if you remove the structural transmission there is still the airborne to contend with, possibly placing the turntable in an entirely different room? I actually tried this difficult to A/B test but I think I preferred the sound with the turntable in with the loudspeakers.
Isolation under anything else is extremely questionable, many commercially available devices are pretty much ineffectual, 'cup and ball' designs for example offer no isolation whatsoever in the vertical plane what, placing 'decoupling' under loudspeakers will NOT drain vibration from the loudspeaker, will NOT tighten the bass, it will NOT remove colouration.
The loudspeaker's designer has to ensure that the loudspeaker's enclosure does not store energy which could lead to colouration, isolation will not make the slightest difference.
Remember that their is structural borne vibration transmission and their is airborne transmission the actual air pressure changes from which sound is derived.
Also consider that vibration has to be of a sufficient amplitude to create AUDIBLE resonance.
Placing feet under your loudspeakers will bring the tweeter up which might change the sound slightly depending upon the vertical dispersion characteristics of the loudspeaker.
Amplifier stands even more ridiculous, I suppose they might though save you from stubbing you toe.
If you purchase blameless electronics, ie designs which do not add audible distortion and which are capable of properly driving your loudspeakers if you marry those to a really fine measuring pair of loudspeakers ( just look for any measurement led manufacturer) then really that is it.
I would always advise acoustically measuring your room and including in your signal chain some provision to implement EQ, reducing any 'boom' from room derived standing waves can bring a huge improvement. Quite possibly the largest single improvement to sound quality one can ever make, playback software, dacs and streamers now all can include EQ.
Remember HI-FI is electrical engineering, good measurements mean a transparent sound, you can't get better than that, of course you can buy a more expensive box, pride of ownership etc but it simply can'
t sound better than audibly transparent, just glance at the dac and amplifier measurements over at ASR, blameless electronics are available and relatively inexpensive.