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RF Interference in Speaker Cables??? (video)

johnnyx

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We know that Class AB amplifiers can demodulate AM RF signals applied to the speaker terminals, but I suspect that Class D amplifiers would not suffer in the same way - they have an output filter with a capacitor directly across the speaker wires.
 

pma

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We know that Class AB amplifiers can demodulate AM RF signals applied to the speaker terminals, but I suspect that Class D amplifiers would not suffer in the same way - they have an output filter with a capacitor directly across the speaker wires.

No universal answer here. Better class D amps have the output filter inside the FB. And e.g. NC400 is prone to frequencies near 2 x Fosc and demodulates/intermodulates it into audio band. There are no simple answers, guys. You need to investigate everything, thoroughly.

Hypex 900kHz inp.png
 

abdo123

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It’s interesting how this thread went from ‘you shouldn’t worry about RF interference’ to ‘you should worry about RF interference, it’s just that the amplifier is what you should be looking at, instead of speaker cables’.
 

Francis Vaughan

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you should worry about RF interference, it’s just that the amplifier is what you should be looking at
Worth saying that, for the large part, a properly implemented amplifier not subject to unusual RF interference is in the category of "not a worry". We don't worry about acoustic interference in the form of tiny tiny noises from ordinary acoustic sources. None of us have silent listening rooms. There is always a little but of leakage from outside. Any residual interference in our audio gear might well be the cause tiny intermodulation products, but generally at levels well below audibility.
Whilst RF can be an evil beast in the extreme, in reality, measures to protect audio equipment from interference from domestic sources have been taken by the designers, and any unexpected issues are not dreadfully hard to address. But in the arsenal of measures, braiding speaker cables doesn't exactly rank well. Magic construction cables even lower.
Where the idiocy gets tiresome is this stupid mantra that any possible source of distortion must be rooted out (the any junk in the way argument), and done so with the magic cable/connector/stones/crystals/isolation-pads/hockey-pucks/quantum-putrifiers being sold by the person making the argument.
 

Lambda

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Since it's Inherently hard to proof an negative (simpler words) i try to give him the best benefit of the doubt.

Two Speaker wires going to two speakers act act like a dipole antenna.
https://upload.wikimedia.org/wikipe...ceiving_antenna_animation_6_800x394x150ms.gif
(amirs test only used one speaker wire?)

How long this wires are and the speakers apart diktats the antenna tuning
https://www.everythingrf.com/rf-calculators/dipole-antenna-length-calculator
Maybe 20-200Mhz seems reasonable.

but what is an "normal" level of RF? We don't know. but we know a maximum.
502_2020_791_Fig1_HTML.png


So less ~30V/m in an uncontrolled environment for the general public

https://www.giangrandi.org/electronics/anttool/rx-field.shtml
30V/m @ 100mhz gives us ~32dBm in a ~ 70Ohm load (ignoring antenna gain)

What's the impedance from left the speaker to right speaker at 100MHz? We have no idea! probably not 70Ohms.
Assuming 70Ohms anyways we would get ~20dBV RF at the amplifier's output.

Of cause we don't hear this but what we hear is the amplifiers demodulation.
How good (bad) dose the amplifier demodulate? We don't know!
https://www.ti.com/lit/an/snoa497b/snoa497b.pdf?ts=1613746884506
It depends on the amplifiers "EMIRR"
But i only find data for integrated amplifiers ranging from -5 to 100dB

Assuming 20dB EMIRR we wold get an equivalent input offset voltage of -20dBV
with a typical amplifier gain 32dB we would end up with 12dBV offset into the speakers about
About 4V RMS into the speakers (maybe most of the amplitude is DC)

All of the vales are made up and lean to the worst case scenario.

As long as we don't know Amplifier output EMIRR and impedance at HF all this is speculation
Its defiantly not entirely impossible but unlikely.
its very unlikely braided magic cables make a difference!

A 25cent ferrit can make a difference!
 
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solderdude

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So less ~30V/m in an uncontrolled environment for the general public

With field strengths of 30V/m no one is allowed into the anechoic test chamber, not even at 10V/m.
These are merely immunity numbers certain equipment must be able to deal with without affecting its performance.
The latter is a bit hard to define with audio.
It is NOT what you have in your home unless you maybe wrap your speaker wire around a wifi antenna or phone.
The moment a few cm away from such an RF source it drops fast.

What Amir showed was the 'open end' (not really open as it was terminated, probably 50 or 75 Ohm I assume)
When the voltage would be measured at the output terminals of the amplifier (and that will differ from other amps) the micro to nano volts present would be even lower.
The chance of an audio amplifier amplifying anything above 1MHz is very very small. Well some amps can go a bit higher.

What can happen is the AM demodulation which gives detection and thus the sound of the radio station. A large power FM transmitter very nearby can introduce some DC (or low hum).

Braided and twisted cables can help lower the induced (and extremely small RF) signals, so can ferrites.
This however is ONLY needed when powerful transmitters are close by and one hears that radio station.

I would recommend everyone to forget about this nearly always non-issue. The very few people that do receive a radio station are far more likely it is 'received' by other means than the speaker cable.
 

respice finem

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Words have meanings. People who stick to them are easier to understand than those who invent their own.
Certainly, I wouldn't be happy too if we had to rewrite half the language, and especially technical terms, every generation. So, yes, assuming he knew about the other meaning, he should have called it differently. But otherwise, he's right about this certain, well, confusion.
 
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PeteL

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No universal answer here. Better class D amps have the output filter inside the FB. And e.g. NC400 is prone to frequencies near 2 x Fosc and demodulates/intermodulates it into audio band. There are no simple answers, guys. You need to investigate everything, thoroughly.

View attachment 113724
What are we looking at?
 

RichB

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We won't hear 100 MHz, but RF can enter audio circuits via cables and get demodulated. It can result in offset shifts in opamps, for example. See fig. 11 in this app note: https://www.ti.com/lit/an/snoa497b/snoa497b.pdf
Don't believe me? Hold a GSM cell phone near an old transistor radio and call the phone. You'll hear a "burr, burr, burr" sound just before the phone rings. You can also toggle airplane mode. As the phone reconnects to the cell network, you'll hear the interference as well. That said, a cell phone transmits at up to 2 W RF power (+33 dBm). Much higher than the -60 dBm Amir measured.

Wifi is a common source of interference as well. The SSID broadcast will create tons of spurs at multiples of 30 Hz that my APx 525 will happily pick up from any circuit sitting on my lab bench. A metal chassis works wonders for keeping that RF out, though.

RF usually enters audio circuits via the input, not the output as the output has much lower impedance. Not thereby said that RF cannot enter through the output of an audio amp. I recall various HAM radio books explaining how to address RF entry with ferrite rods and/or cores.
Modern consumer electronics are supposed to be somewhat RF tolerant (at least if they're marked with the CE or FCC logos). They're also supposed to "play nice" and not emit or conduct RF out of the chassis.

That said, I find it exceptionally unlikely that a different speaker cable would somehow prevent RF entry, though. That part is snake oil.

Tom

I have my gear in credenza and at one point stashed the Wifi router behind there. It caused the Sonica DAC to pickup a mechanical whine on the outputs.
There was never noticeable impact on the amplifier outputs. I have since move to a Unify wall and ceiling mounted network and there are no issues.

I am amazed the components that source components with Bluetooth can get excellent SINAD results.

- Rich
 
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Cbdb2

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Two Speaker wires going to two speakers act act like a dipole antenna.
https://upload.wikimedia.org/wikipe...ceiving_antenna_animation_6_800x394x150ms.gif
(amirs test only used one speaker wire?)

How long this wires are and the speakers apart diktats the antenna tuning
https://www.everythingrf.com/rf-calculators/dipole-antenna-length-calculator
Maybe 20-200Mhz seems reasonable.

Speaker outputs are seperated so no. Think of 2 mono blocks, theres a very high impedance between the 2 speaker outs. And each speaker cable has 2 wires usualy one to ground, so not a dipole antenae unless the cable is split at the end and bent into a dipole.
 

Lambda

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Speaker outputs are seperated so no.
thats what i'm showing
Think of 2 mono blocks, theres a very high impedance between the 2 speaker outs
Why do you think so?
2 mono blocks wound share a Ground and not be high impedance to each other.

And each speaker cable has 2 wires usualy one to ground,
As shown in my schematic. If its a full bridge amplifier there is no speaker cable going to ground.

so think of it as a dipol antanna and each dipole is made of 2 cables with a speaker at the end.
 

Cbdb2

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First, your making a dipole (2 pole) with 4 wires. Second, a dipole has an RF impedance of around 75ohms, which should be matched by the amp input. Whats the impedance between the the positive speaker out of your left monoblock and the positive speaker out of your right monoblock?
 

Lambda

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First, your making a dipole (2 pole) with 4 wires
Yes it could be 100 wires close together, it dose not matter for this.

Whats the impedance between the the positive speaker out of your left monoblock and the positive speaker out of your right monoblock?
What's the impedance from left the speaker to right speaker at 100MHz? We have no idea! probably not 70Ohms.
Assuming 70Ohms anyways we would get ~20dBV RF at the amplifier's output.

Yes there can and most certainly is is an impedance miss match.
 

Cbdb2

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A dipole has 2 wires, or its not a dipole! Show me a RF reciever with more than 2 conections at the input. Your making stuff up.
 

Lambda

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Cbdb2

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What? A dipole antenae is one wire now, earlier it was 4 wires. This is straight from your link: "This type of antenna is known in America as a "folded unipole", which has been extensively studied by John H. Mullaney."

This was my education on antenae: https://www.ece.ubc.ca/course/elec-411

Whats yours, regurgitating wiki posts? Im done here.
 
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ehabheikal

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I buy decent quality cables, proper copper, good looks, good plugs, reliable and durable. All this you will get in a 20$ cable. A 200$ cable? 2000$? Keep this for the subjectivists in audio.
 
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