A good oscilloscope will be our friend here.
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We may need your ears for our experiment, keep training!
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Valves are well known for changing over time, I thought.
They are metal and glass. Why cables of metal and plastic cannot change?
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It’s not that simple. The valves have a heater in them, which heats of an electrode, which emits electrons. But not just electrons - over time the glass envelope darkens because of the metal atoms that are also released (or evaporated), and condense on the envelope - as well as on other parts of the valve. There are visible and obvious changes - an old valve can be identified quite easily. Can you identify an old cable? Back in the day, yes you could - the insulation degraded over time, particularly the early wires with rubber insulation and/or cotton. These days - no.
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I am waiting for advice on how to perform a crystallographic analysis in a cable. Then I will request a quotation from a laboratory. We shall see.
Point 6 of my procedure.
…and ethics approval if there will be listening tests using human subjects.
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I agree, in not familiar system it would be more difficult to identify. And at dealer place for example, we are less relaxed and confident vs listening to our own system.
I have no friends with very resolving system, so can’t test outside of dealer place, for a non familiar system.
I agree, it’s a bit like training. When I begun the audiophile journey, 25 years ago, I was not able to discern the details and different aspects as soundstage….as accurately as today.
But I know there will be a decrease too….in some years.
I am purchasing cables for the experiment. This group has any preference?
Mogami or Qed?
Any other?
QED will be familiar to many people on here. Most of us will have had some at some point in our HiFi journey.
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I don’t see a problem with measure but not hear…
That simply means that ‘burn in’ is a physical phenomenon, but IN THIS TEST, the difference was insufficient to be detected by the playback system. It says nothing about other systems! 
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Thermionic valves change their characteristic over time…
Cathodes change and erode.
Cathode heaters change as they evaporate.
The physical geometry is altered by heating and cooling cycles.
I thought that the effect was supposed to be very obvious…
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Both replies to my post about the Russians explain why valves change.
@Xanthe, @Beachcomber, please explain why cables do not change.
Is this the subjective bias we are talking about?
Seems appropriate
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Firstly I’m not saying that cables DON’T change…
Everything changes, metals oxidise, crystal boundaries relax; polymers creep, relax, depolymerise and evaporate, etc, etc.
(Or Buddhist philosophy: “All states are subject to change.”)
However:
The metals used in cable construction (mostly copper and tin) change so slowly: significant oxidation takes years for high purity copper, unless subject to considerable stress (>80% of elastic limit) or heat (>400°C) changes to the crystal boundaries take decades to change by tiny fractions of a percent. Tin is even more resistant to oxidation, but the crystal boundaries can change more easily (due to the lower annealing temperature and lower elastic limit). Even then solder joints change fairly quickly just after forming and then remain essentially stable unless subject to considerable force (in the GPa range!)
Some plastics are a lot less stable, but those used for the dielectric are much more stable - although PTFE is an exception here, it does suffer significant issues with creep at relatively low pressures. However even those levels of pressure would be considered abuse when applied to audio cables!
The problem is a lack of any clear mechanism for change in the tens to hundreds of hours timescales. Stress on solder joints is possible and (with PTFE only) creep due to long term flexion is possible. Creep in PP or XPE dielectrics is likely to be less the 100ppm, and other processes are only likely to result in bulk changes below the 1ppm level!
To asses things in more detail will require very deatiled study of changes to the properties of materials (e.g. micro XRF, crystallographic analysis, TEM, proton beam scattering etc.).
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And then compare these tiny, if existing, changes with the malleability of the human mind…
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Absolutely (but I prefer plasticity rather than being hit with a hammer!).
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