Testing different cables for a subwoofer faint hum and I got surprising results so far. lol

[GabrielPhoto]

So I was cleaning of my wiring and decided to test some cables for noise floor, hum etc.
With my gazillion connections I do get a faint hum on my subs if I remove the jensen ISO-MX that gets rid of it, so I figured that would be a good way to test RCA cables to see if any make a difference.
Well turns out they do change the level of that hum substantially.
Some were about 4db louder than the best.
For example, a WBC was 2.5- 3db louder than the best cable which turned out to be a SKW cable which on top of that was the longest at 16.5 vs 12' for the others or so. Basically with the SKW the difference between the hum with and without the was about 1 db.
Other surprisingly not so good cable was the Mediabridge which I have been recommending and using often.
I recall SKW being pointed out about their copper purity or something like that so I am surprised that so far it was the best of all I tested. lol
I have a Silver Serpent cable I am planning to test to just for kicks.
In any case, it was a curiosity test while cleaning up my wiring and was not expecting much if any differences.

 

[DVDdoug]

I'm surprised too!

Usually we say "cables don't make a difference" but that assumes the cables are appropriate for the application and not defective or broken.

But one cable might be better shielded than another. If it's shielding, moving the cable around will usually make a difference depending on how close it is to the "hum source", etc. Or grabbing an unshielded cable with your hand will usually make it worse. A longer unshielded or poorly shielded cable will also usually be worse.

Copper "purity" or silver shouldn't make a difference. I'd also be surprised if wire gauge made any difference. A slightly corroded connector might pick-up more noise.

Sometimes a shield that's broken/disconnected one one end can eliminate a ground loop and reduce noise. (The shield still works connected at only one end and you need another signal ground somewhere else... Usually NOT the recommended solution, especially for unbalanced connections.)

Or... Just making two measurements a few minutes, or a few hours or days, apart might make a 1dB difference.

 

[GabrielPhoto]

I'm surprised too!

Usually we say "cables don't make a difference" but that assumes the cables are appropriate for the application and not defective or broken.

But one cable might be better shielded than another. If it's shielding, moving the cable around will usually make a difference depending on how close it is to the "hum source", etc. Or grabbing an unshielded cable with your hand will usually make it worse. A longer unshielded or poorly shielded cable will also usually be worse.

Copper "purity" or silver shouldn't make a difference. I'd also be surprised if wire gauge made any difference. A slightly corroded connector might pick-up more noise.

Sometimes a shield that's broken/disconnected one one end can eliminate a ground loop and reduce noise. (The shield still works connected at only one end and you need another signal ground somewhere else... Usually NOT the recommended solution, especially for unbalanced connections.)

Or... Just making two measurements a few minutes, or a few hours or days, apart might make a 1dB difference.

Yeah I went back and forth between cables many times and it was a consistent result. If anything the SKW seems like the skinniest cable so I figure it would have the worst performance if there was going to be a difference LOL

 

[MaxwellsEq]

So I was cleaning of my wiring and decided to test some cables for noise floor, hum etc.
With my gazillion connections I do get a faint hum on my subs if I remove the jensen ISO-MX that gets rid of it, so I figured that would be a good way to test RCA cables to see if any make a difference.
Well turns out they do change the level of that hum substantially.
Some were about 4db louder than the best.
For example, a WBC was 2.5- 3db louder than the best cable which turned out to be a SKW cable which on top of that was the longest at 16.5 vs 12' for the others or so. Basically with the SKW the difference between the hum with and without the was about 1 db.
Other surprisingly not so good cable was the Mediabridge which I have been recommending and using often.
I recall SKW being pointed out about their copper purity or something like that so I am surprised that so far it was the best of all I tested. lol
I have a Silver Serpent cable I am planning to test to just for kicks.
In any case, it was a curiosity test while cleaning up my wiring and was not expecting much if any differences.

Line level cables should all behave roughly the same, in perfect circumstances.

But if there are high levels of mains frequency interference or radio transmission, line level cables can behave differently. If the input stage of the receiving end is sensitive to RF or mains interference, line level cables may also make a difference. Single Ended working (e.g. RCA) is also sensitive to noise because there is no differential working to eliminate common mode noise.

Ideally, you should aim to minimise the noise sources.

 

[KSTR]

In any case, it was a curiosity test while cleaning up my wiring and was not expecting much if any differences.

When you have a "ground loop" the amount of hum you get is strictly proportional to the (unbalanced) cable's shield resistance. The well-known Ohm's law at work, voltage is current times resistance.
And "ground loop" means exactly that, a parasitic current flowing from component A to to component B on the shield of cables. With unbalanced cables, the shield is part of the "signal circuit" and you get hum, whereas with balanced cables the shield is not part of the circuit, thus no hum but the current is still flowing.

 

[Bruce Morgen]

With unbalanced cables, the shield is part of the "signal circuit" and you get hum, whereas with balanced cables the shield is not part of the circuit, thus no hum but the current is still flowing.

Is that the reason for the separate -- or physically parallel but electrically connected to the shield only at the plug a la the old AR XA -- ground leads used to connect turntables to phono preamps? Obviously the voltages involved are much lower than line level, which one would think makes such a circuit even more hum-susceptible.

 

[chervokas]

So I was cleaning of my wiring and decided to test some cables for noise floor, hum etc.
With my gazillion connections I do get a faint hum on my subs if I remove the jensen ISO-MX that gets rid of it, so I figured that would be a good way to test RCA cables to see if any make a difference.
Well turns out they do change the level of that hum substantially.
Some were about 4db louder than the best.
For example, a WBC was 2.5- 3db louder than the best cable which turned out to be a SKW cable which on top of that was the longest at 16.5 vs 12' for the others or so. Basically with the SKW the difference between the hum with and without the was about 1 db.
Other surprisingly not so good cable was the Mediabridge which I have been recommending and using often.
I recall SKW being pointed out about their copper purity or something like that so I am surprised that so far it was the best of all I tested. lol
I have a Silver Serpent cable I am planning to test to just for kicks.
In any case, it was a curiosity test while cleaning up my wiring and was not expecting much if any differences.

It's kind of cable shielding 101, as @KSTR said above, in unbalanced audio when you have noise current on the shield/return line, the noise voltage level at the input of the load device is going to be proportional to the resistance of the shield/return conductor -- lower resistance shielding/return will give you lower noise voltage, higher resistance shielding will give you higher noise voltage (V=IR). For the application, given cables that are otherwise identical (including in length), you'll have lower noise in the presence of AC leakage on the shield, with lower resistance shielding -- so, thicker double copper braided shielding vs. single copper braid or braid plus aluminum foil or just foil; also shorter cable is obviously going to present less resistance than otherwise identical longer cable.

 

[chervokas]

Is that the reason for the separate -- or physically parallel but electrically connected to the shield only at the plug a la the old AR XA -- ground leads used to connect turntables to phono preamps? Obviously the voltages involved are much lower than line level, which one would think makes such a circuit even more hum-susceptible.

Typically in a turntable grounding scheme, the ground leads are connected to the tonearm tube and turntable bearings. They do help turn a metal tone arm tube into something of a shield for the signal wires within, kind of akin to the shield in a balanced cable, but they're not part of the signal path the way the shield is the return in a coax with unbalanced audio.

 

[KSTR]

Is that the reason for the separate -- or physically parallel but electrically connected to the shield only at the plug a la the old AR XA -- ground leads used to connect turntables to phono preamps?

No.
Those cables that you mention are basically the worst cable you can make from the given materials.
Any parasitic ground current must go through that small inner conductor and the shield is quite ineffective. For turntables which a are floating sources there is (almost) zero parasitic ground current and for this application these cable can work without trouble.

The #1 rule for universal unbalanced interconnects is keep them as short as possible and with the heaviest shield one can find (best conducting ground connection)

 

[Vladimir Filevski]

For example, a WBC was 2.5- 3db louder than the best cable which turned out to be a SKW cable which on top of that was the longest at 16.5 vs 12' for the others or so. Basically with the SKW the difference between the hum with and without the was about 1 db.
Other surprisingly not so good cable was the Mediabridge which I have been recommending and using often.

Quality of the shielding in cables is variable, so that is one of the factors which may contribute to the hum.
Check for the oxidation in RCA connectors, too - even in the new ones. For really indisputable cable comparison test you should solder identical RCA connectors to each cable and then to compare.

 

[kazuviking]

I would really like seeing a silver plated copper cable with the silver coating being fully oxidized to see how much it improves/worsens the hum. In theory oxidied silver is a really good RF insulator.

 

[pskaudio]

I never had a single problem with cables that hum since the cables I use always know the words. Of course they are made with materials from another dimension, cost more than most single family homes and are rated Class A++++++++ by Stereophile's editors. They also might be causing a small tear in the fabric of space time, but they sound amazing.

 

[GabrielPhoto]

I never had a single problem with cables that hum since the cables I use always know the words. Of course they are made with materials from another dimension, cost more than most single family homes and are rated Class A++++++++ by Stereophile's editors. They also might be causing a small tear in the fabric of space time, but they sound amazing.