The short answer is that RF interference can enter an amplifier ANYWHERE.
It can get in through the input interconnects, or the power cable, or even through the air if the chassis isn't well shielded.
The most common way it gets in through the speaker cable is by getting into the negative-feedback loop going from the output back to the input.
Tube amplifiers are especially prone to this because they tend to operate at high impedance and many vacuum tubes will amplify radio frequencies quite well.
In really well thought out tube designs specific resistors or inductors are included in certain locations to prevent this (ones with deliberately limited high frequency response).
Semiconductor junctions can also rectify and detect AM radio frequencies... although this is a problem I haven't seen more than once or twice in decades.
(But it used to be relatively common... especially when CB radios were popular.)
There are TWO basic problems with solving problems you don't have (or maybe three):
1. You can spend a lot of money and receive no benefit.
1a. You can spend money that could have been better budgeted SOMEWHERE ELSE.
For example, spending $1000 more on a better pair of speakers will get you far more than wasting it on $1000 speaker cables.
2. Sometimes so-called solutions to one problem create a new and different problem.
For example those really cool super shielded cables that block the RF interference you DON'T have may have so much capacitance they cause your amplifier to oscillate.
The result could be that you blow your amp, or your speakers, or simply that it sounds worse instead of better.
(And it's sort of funny how people who obsess over one particular problem often fail to pay attention to other problems and risks.)
There is a notorious case where a certain brand of expensive speaker cables would cause certain otherwise excellent amplifiers to blow their fuses.
(Always, all the time, the minute they were turned on... to the point where it became sort of an industry joke.)
(Note that they did work just fine with many other models of amplifier...)
Although, to be fair, other than making impressive claims, I'm not sure if those wires actually solved ANY real problems or not.
In all fairness I don't see any obvious such risks with braided cable...
Although the possibility that the insulation would get crushed, and the conductors would short, really would worry me about braided wires with Teflon insulation.
So I would be extra careful that they don't get crushed or stepped on.
(This has been a known weakness of Teflon insulation ever since it was invented.)
I should also point out that "demonstrating that special speaker cables read less on an FM signal strength meter" doesn't prove much at all.
(Other than that they make a really lousy FM antenna... )
FM radio signals are really NOT the sort of signal that I would ever expect to bother an amplifier.
Doesn't it seem odd that they couldn't come up with ANY SORT OF TEST that would show that their wires would actually help where you would be using them?
Couldn't they come up with a test, no matter how contrived, that showed their wires did well at blocking the actual sort of noise you might have a problem with?
Like the sorts of noise made by car ignitions, and fluorescent lights, and light dimmers, and WiFi routers...
I'm afraid I cannot even give them a "B" for effort.
KeithL, If... And I say If... Rf signal can be catch by speaker cables... Could it be catch by the amplifier input cables (Rca)? And be amplified by the amplifier? than be heard?
I know nothing about those phenomenon and have no problems with Rf... but If I was nuts about it or selling cables I would be more worried by the input cable than the speaker one to catch sh** in the signal.
