> Interference isn't a problem in speaker cables because it is an amplified signal, so any added noise is too little to be audible.
I dispute that. Source: I could hear at a previous apartment where I used to live that something was off when I was listening to music. It was subtle, but it was there. It drove me mad until I realized that by lifting the speakers cable off the floor the interference was gone.
I don't care about the science in this case. I just don't for I've witnessed it myself (well, heard it really). I've tested my theory (lifting the cable of the ground) and repeated the experiment. It is a fact (for you it may just be a comment on the Internet, but for me it is factual).
Putting the cables on little wooden pieces I made got rid of the interference (at least I couldn't hear it anymore).
That was happening on a "budget" (less than $1 K) setup (including a DAC). Very clean source: bitperfect rips of my CD collection.
Quiet room. The added noise was noticeable and was perturbing the listening.
If there was interference then you would _always_ hear it, not just when playing music. In fact, it would be significantly easier to hear it when not playing music.
Weird things can happen. If you pick up RF on the speaker wire, it can make the output stage of the amplifier nonlinear in weird ways.
The extreme case is when you can receive radio signals on the speaker wire that are rectified and amplified by the amplifier; but you can get wonkiness short of that.
I've fought these arcane issues before. I don't have a ton of experience in audio, but I've seen them at lower frequencies (in servo amplifiers, where rectified RF causes DC offsets) and higher frequencies (as intermodulation in RF amplifiers from strong out-of-band interfering signals).
This is why you find things like this in design manuals. These are focused on offset errors in instrumentation amplifiers hooked to long cables (but intermodulation is an equal or larger concern in applications that care about frequencies above DC):
"In addition to filtering the input and power pins, amplifier outputs also need to be protected from
EMI/RFI, especially if they must drive long lengths of cable, which act as antennas. RF signals
received on an output line can couple back into the amplifier input where it is rectified, and
appears again on the output as an offset shift."
Microchip says the same thing: "Amplifier outputs also need to be protected from
EMI/RFI, especially if they must drive long lengths of
cable, which act as antennas. RF signals received on
an output line couple back into the amplifier input
where they are rectified and appear again on the output
as an offset shift."
Note that I'm not really saying you need anything special on speaker cables, other than common sense: don't separate the pair for as much of the run as possible, and make sure the terminations at the end are not total garbage. If you have strong RF sources nearby, like when I had a 50W HF transmitter in my apartment, you may need to add RF chokes/ferrites on the amplifier end of speaker cables to reduce interference (I did).
Indeed, the ARRL (American Radio Relay League, an amateur radio association) describes that adjusting speaker cables is a frequent way to cure interference for neighbors of people with high power transmitters:
"Speaker wires are often 8 to 16 feet long. When you put two of them together, you make an efficient receiving antenna. Try bundling the speaker wires to reduce their effectiveness as an antenna. This procedure has been known to eliminate the interference all by itself."
"A: For a detailed explanation, you can refer to the ARRL Handbook's section on controlling RFI, and the section of the ARRL web site on EMI/RFI Products and Other Resources. You can build two of them, one for each speaker output. Wrap ten to fifteen turns of speaker wire onto an FT-140-43 ferrite core. Use an FT-240-43 if the speaker wires are large, and use "73" material for interference from 80 or 160-meter signals. Alternately, type "31" material is an excellent general purpose choice for HF. Install them right at the amplifier. If the system uses amplified speakers, you should install one at each speaker, too."
This is all covered in the video I linked. Your whole post is classic HN. Waste everyone's time with irrelevant information. There is a reason it's not easy to find shielded speaker cables. It's not needed.
Dude, if people fix RFI problems by shielding speaker wires and putting ferrites close to the amplifier on speaker wires, clearly speaker wires are antennas for RFI that can affect amplifier performance.
Asking me to figure out what you're arguing based on a 17 minute video is not reasonable. I skimmed the video and took my best guess of what you're advocating. (It's not a representative or useful test; yes, it's harder to measure RF on a cable when it's plugged into an amplifier, but that doesn't tell you that RF on cables can't be rectified and amplified by the amplifier). You can use your words yourself.
In any case, the people who have asserted that RFI can get into ampifiers from speaker wires and cause problems are correct.
Your assertion "this is not an issue for anyone" contradicts the direct experience of lots and lots of people who have lived close to large RF sources and had RFI problems in audio fixed by adjusting speaker wires, such that it's the first step for engineers and radio amateurs working with angry neighbors.
It’s quite simple. I am asserting that interference on speaker wire running from an amplifier to a passive speaker doesn’t matter. Saying otherwise was invented by snake oil peddlers and you are doing harm with your akshually act.
RFI on a speaker wire going back to the amplifier is a big problem. As evidenced by all those sources.
Buying more expensive cables isn't generally the cure and is snake oil. Indeed, shielding itself can add enough capacitive loading to actually reduce speaker high frequency response.
But having to put in an RF choke on speaker wire to prevent RFI from having negative audible effects is common. And using a little bit of care to keep as much of the cables paired as possible, keeping runs as short as reasonably possible, and making reasonably good terminations is good insurance against it being a problem for you.
I've given plenty of high quality evidence, while you've given a long video of someone making a measurement that is meaningless to what I'm asserting.
> You have provided no evidence someone can walk into a store and buy an amp, speakers, and speaker wire and suffer any problems due to RF interference.
The ARRL wouldn't have to help neighbors of amateurs put chokes on speaker wires if this couldn't happen.
Most of us have the experience of having a cellphone close to speaker wiring and hearing LOUD buzzes and clicks. It was a bigger problem in the AMPS days (with higher output power), and more often the interference gets into the amplifier by signal lines than it does by getting in through power lines and speaker wires, but it can certainly go in the output (or power) as well. Have you never experienced this?
I still remember the first time I experienced this. I was 12, returning from a road trip with my (older) sister and her significant other's family, where we had handheld CBs. The hifi inside the house was demodulating and amplifying our CB signals; they could be clearly heard when we used the CB from the driveway. 5 meters of speaker cable was a good antenna for a 10 meter wavelength RF signal; a poorly filtered amplifier stage was demodulating and amplifying the signal.
Interference will not generate significant current in the cables, but for a sufficiently long run, it can generate measurable voltages at your amplifier output. Depending on the power stage, this can cause your amplifier to react to the interference (e.g. if there is high-impedance negative feedback). With just the correct setup, a poorly designed power stage, and a long enough speaker cable run, you can pull in an AM station.
If you have a reference showing audible noise resulting from interference on a speaker cable running from an amplifier to a passive speaker then please share it.
Class-D amplifiers pump out a signal literally buried in noise. You can't hear it because it's all shifted beyond human hearing and filtered by the speakers.
Class-D amplifiers are basically PWM run through some capacitors as a low-pass filter. The speakers are not what do the filtering, it's the capacitors.
In the video I linked, he was unable to induce any noise into the speaker wires greater than -130db at 60hz. The threshold for human hearing in absolutely ideal circumstances is about -115db. Anything less than that is provably inaudible for all frequencies, and for 60hz the threshold is much higher than -115db. The noise floor of the room only raises that further. For perspective, the very best state of the art DACs can only keep noise levels to -123db and just a few years ago the number was significantly worse.
Where the triangle isn't perfectly linear. If any RF gets into the output, it can be converted to audio frequencies by the nonlinearity and amplified. The open loop gain of the amplifier component can increase the magnitude of signals like this by tens of decibels.
Nah-- it's about high frequency noise getting in via the speaker lead, and coupling to the negative feedback of the amplifier stage, and getting rectified and amplified.
Yes, most interference is via line level inputs, but it can easily be via the "output" as well.
