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Topic: Is it safe to run speaker cables next to AC ones? (Read 13007 times) previous topic - next topic
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Is it safe to run speaker cables next to AC ones?

Reply #25 –
Quote
Hm... can you fill me in with the theory I'm missing here? I mean, you get an identical interference waveform applied to both connectors of a speaker. The waveform applied to both ends of the coil induces no current thereby canceling itself. Doesn't it happen in plain old telephones exactly like that?

Hmm, yeah, perhaps you're correct in the case of a speaker since it simply moves in relation to the difference in voltage on the two wires.

The twisted pair in telephones is only one part of a two part system. There is also electronics on either end of that twisted pair that are taking measures to ensure the desired signal is retained and undesired signals are discarded. It isn't only the twisting of the wire that does this. Telephones are balanced devices, that is, the voice/audio signal is present on *both* wires and is in opposite polarity on each wire. Those two signals are then taken by a difference amp, which outputs a single signal which comprises only the differences between the two original signals. Interference will be the same on both those signal wires, and thus will be eliminated by the subtraction process in the difference amp. Since the intended signal is intentionally opposite, it remains intact after being subtracted from one another. Consider this:

signal = +6
put through balanced system 'transmitter' which duplicates and inverts the signal on wire2.
signal1/wire1 = +6
signal2/wire2 = -6
transmit across wire pair and then received by balanced system 'receiver' which subtracts signal2/wire2 from signal1/wire1.
((+6) - (-6)) / 2 = +6

interference = +5
signal1/wire1 = +5
signal2/wire2 = +5
(+5) - (+5) = 0

Is it safe to run speaker cables next to AC ones?

Reply #26 –
Quote
Hm... can you fill me in with the theory I'm missing here? I mean, you get an identical interference waveform applied to both connectors of a speaker. The waveform applied to both ends of the coil induces no current thereby canceling itself.

I thought that as soon as this topic was posted. But on further thought, though the same interference would hit both + and - cables, they can be connected differently within the amplifier. Thus, each cable sees a slightly different impedance, and the same interference will induce a different current. So, there's a theoretical reason why you might hear something at the speaker.

As I've already said: in practice, forget it.

Cheers,
David.

Is it safe to run speaker cables next to AC ones?

Reply #27 –
hmm, good point, hadn't thought that far about it

Is it safe to run speaker cables next to AC ones?

Reply #28 –
Quote
Hm... can you fill me in with the theory I'm missing here? I mean, you get an identical interference waveform applied to both connectors of a speaker. The waveform applied to both ends of the coil induces no current thereby canceling itself. Doesn't it happen in plain old telephones exactly like that?

Yes, your analysis is correct, up to a point.  Two wires next to each other will see the same voltage in the same phase caused by "voltage" pickup from a power line through distributed capacitance, whether they're twisted or not.  What happens as a result of the connection impedances in the loop, whether nonlinear or not, will affect the current flow.  Twisting the wire doesn't help in reducing this interference. 

A pair is actually twisted for a different reason.  The source of interference being addressed is voltage developed from magnetic flux passing through an area surrounded by a closed, conducting wire; like the coil in a motor.  This is the main source of interference pickup from AC voltages ( it doesn't exist with DC voltage sources).  Twisting a pair keeps the area through which a magnetic field can pass, small and the induced voltages are cancelled between twists. 

I was looking at this interference issue because I'm rewiring my family room (USA) with wires for a 5.1 speaker system, and one of the wiring manuals from a supplier of media systems suggested keeping speaker wire in the walls 3 to 4 ft away from power lines.  This seemed very excessive to me, and almost impossible, so I started looking for information.  I joined this group to respond to some comments on this issue.

The comments by those of you who have never seen a disturbing interference have helped me a great deal.  I intend to pretty much ignore any risk from power line interference like 60 cycle hum.  I will not install a speaker line for any distance next to a power line, but I intend to cross over one or more, and go through common holes in a 2X4.

I also plan to use simple 16 AWG (not twisted) 2 conductor speaker wire.  The contentious arguments over wire, coatings and connectors on this and other forums have resulted in completely unsupported conclusions.  I'm surprised at the small amount of science in arguments of many of the commercial companies.  The only parameter that matters, within the bandwidth of the audio spectrum, is the total resistance between the amplifier and the speaker.  Period.  In fact, with modern feedback audio electronics the importance of that parameter is debatable.

Is it safe to run speaker cables next to AC ones?

Reply #29 –
Quote
The only parameter that matters, within the bandwidth of the audio spectrum, is the total resistance between the amplifier and the speaker.  Period.  In fact, with modern feedback audio electronics the importance of that parameter is debatable.

well, no sense wasting power. Or having slightly mismatched levels from short runs to front speakers and long runs to rear speakers. Might as well use some 16AWG or 14AWG wire and not worry or waste. (Even if it would only amount to 1 ohm difference with 24AWG @ 30 feet, still wasting...)
 

Is it safe to run speaker cables next to AC ones?

Reply #30 –
Quote
well, no sense wasting power. Or having slightly mismatched levels from short runs to front speakers and long runs to rear speakers. Might as well use some 16AWG or 14AWG wire and not worry or waste. (Even if it would only amount to 1 ohm difference with 24AWG @ 30 feet, still wasting...)

I agree. 

For solid wire the resistance of 24 AWG wire is about 26 ohms/1000' and for 16 AWG wire about 4 ohms/1000'.  At 30 ft, the 24 AWG wire has 0.8 ohms of resistance and 16 AWG has about 0.13 ohms.  Approximately 20% of your power (with an 8 ohm speaker resistance) will go into heating the wire (2 wires - drive and return).  Wasteful.    Under the same circumstances only about 3% is wasted in heating with 16 AWG wire.  What I've been able to find in the literature is that no listening difference can be detected if the wire resistance is kept below about 5% of a speaker resistance.  So, I'm staying with 16 AWG.  All of my runs are less than 50 ft, and less than 100 watts per channel.   

I'm curious; can hear the difference between near and far speakers using the same gauge wire and no volume adjustability between near and far?

And, back on topic; has anyone actually heard 60 cycle hum with modern electronics and speaker wires too close to in-house power wires?  I'm thinking that it may also depend on what is being powered.  Running an air conditioner or a large motor with high inductance may be more likely to cause problems than just turning on lights.