Speaker Wire vs RCA

[excaliburm]

Why are line-level interconnects (RCA cables) generally coaxial, while speaker wire is typically parallel wires of bare copper? Is it a function of coaxial cables not being able to handle the current?

My understanding of the design of coax (ground shielding the signal) was to avoid both causing and receiving EM interference. Why is this not a concern for speaker wire?

Are running speaker wires for multiple speakers near/on-top of each other a concern?

 

[Deleted member 46664]

The difference is mainly in where they are used and the levels of power they're handling ...

Shielded cables are generally used where sensitive inputs need a clean low level signal. The main purpose of the shield is to keep RF, AC and other kinds of interference off the signal wire so that it doesn't get fed into the input of the next stage.

Speaker wires which are carrying much higher currents and voltages do not suffer from this problem. Anything that's going to interfere with your system at the speaker levels, would likely also cause all the lights in your house to flicker. That is, with low impedance and higher power it takes some serious energy to interfere with them.

There's no problem at all running speaker wires together ... in fact I have more than one installation where I zip tied them together to keep things tidy with no problems at all.

 

[Speedskater]

Why are line-level interconnects (RCA cables) generally coaxial, while speaker wire is typically parallel wires of bare copper?

The best RCA cables are coax with a good shield to reduce interference. They carry almost no current and the circuit impedance may be 10,000 Ohms, so the center conductor may be very small.

Loudspeaker circuits are very low impedance (8 Ohms) and carry lots of current, so both conductors need to be large.

Because loudspeaker circuits are low impedance and high level they are less susceptible to interference.

Loudspeakers could use a large coax, but it would be expensive and difficult to use.

 

[excaliburm]

I see, what about the inverse concern, speaker cables causing interference due to the large amounts of current flowing through them? It makes sense that a lower-power signal can't interfere a high-power one, but why can't two high-power signals interfere with each other? Or is there some reason that the EM levels generated are still low?

 

[Deleted member 46664]

Loudspeakers could use a large coax, but it would be expensive and difficult to use.

Not to mention ugly as sin ...

 

[Deleted member 46664]

I see, what about the inverse concern, speaker cables causing interference due to the large amounts of current flowing through them? It makes sense that a lower-power signal can't interfere a high-power one, but why can't two high-power signals interfere with each other? Or is there some reason that the EM levels generated are still low?

I'm sure that running speaker wires side by side for any long distance could have some effect. But in most setups they almost immediately go in opposite directions so it's seldom a concern.

 

[DVDdoug]

I see, what about the inverse concern, speaker cables causing interference due to the large amounts of current flowing through them? It makes sense that a lower-power signal can't interfere a high-power one, but why can't two high-power signals interfere with each other? Or is there some reason that the EM levels generated are still low?

You can't get enough "interference" into an 8-ohm speaker cable to make ANY sound.

And the voltage & power to a speaker is lower than the "similar" wires carrying the AC power so it's the AC wiring (and transformers) that you have to worry about (with line level signals).

If your RCA cables are properly shielded they won't pick-up interference from either one. In reality, you could probably get-away without shielded cables for line-level connections, but it's not a great idea... If you have a "record player" it's more important... The signals (voltages) are about 1/100th of line level and any noise gets amplified 100X* along with the signal, and the higher impedance makes it "easier" to pick-up interference.

Line level inputs are also high-impedance but line-levels outputs have much lower impedance and when the two are connected together, the low-impedance greatly reduces noise-pick-up in the wires.

Hum is more often the result of a ground-loop, or a broken ground, than from a poorly-shielded cable.


* Power line hum is actually amplified more with a phono preamp because the RIAA EQ boosts low frequencies.

 

[Speedskater]

I see, what about the inverse concern, speaker cables causing interference due to the large amounts of current flowing through them?

The currents in the 2 wires of a speaker cable, are flowing in the opposite direction to each other. So their opposite fields cancel out.