use two parallel cable runs for speaker which is twice as far away? - AVS Forum
Audio Theory, Setup, and Chat > use two parallel cable runs for speaker which is twice as far away?
segmentor's Avatar segmentor 06:22 AM 01-16-2013
I have to wire my surround speakers.

For reasons of misunderstanding I have a quantity of 17AWG cable available for use. In short, the store threw it in with the speakers and told me it's 16AWG suitable for running along the wall edge under the carpet, but it's really 17AWG. I discussed this with the guys in store who still say it's fine for surrounds and it doesn't matter. I'm pedantic though, and I care.

Judging by Roger Russell's much linked-to wire table, 17AWG will do for the left channel. Both speakers are rated at 8 ohms (Polk FXi-A4)

The right speaker requires about 5.5m of cable. (0.09 ohms cable impedance @ 16.61 ohms/km)
The left speaker requires about 12.1m of cable. (0.2 ohms cable impedance)

Is it worth running two pairs of cable from the receiver to the left speaker to halve the resistance, making up for the poor cable gauge?

Will this cause any other issues like different capacitance on the cables to each speaker?

Yes I know I should go out and buy some 14AWG cable and be done with it, but I'd rather use what I have. I also don't know if 14AWG will fit where I need to run it.

JD in NJ's Avatar JD in NJ 06:24 AM 01-16-2013
You can do this. If you did it in order to try and improve your sound they'd call it "biwiring" and usually there's no reason for it. In your case, it could actually help your system, although as you say the cleaner path would be to install heavier gauge wire.
arnyk's Avatar arnyk 06:34 AM 01-16-2013
Quote:
Originally Posted by segmentor View Post

I have to wire my surround speakers.

For reasons of misunderstanding I have a quantity of 17AWG cable available for use. In short, the store threw it in with the speakers and told me it's 16AWG suitable for running along the wall edge under the carpet, but it's really 17AWG. I discussed this with the guys in store who still say it's fine for surrounds and it doesn't matter. I'm pedantic though, and I care.

Judging by Roger Russell's much linked-to wire table, 17AWG will do for the left channel. Both speakers are rated at 8 ohms (Polk FXi-A4)

The right speaker requires about 5.5m of cable. (0.09 ohms cable impedance @ 16.61 ohms/km)
The left speaker requires about 12.1m of cable. (0.2 ohms cable impedance)

Is it worth running two pairs of cable from the receiver to the left speaker to halve the resistance, making up for the poor cable gauge?

Will this cause any other issues like different capacitance on the cables to each speaker?

Yes I know I should go out and buy some 14AWG cable and be done with it, but I'd rather use what I have. I also don't know if 14AWG will fit where I need to run it.

It turns out that two parallel runs of 17 gauge should have the exact same resistance as one run of 14 gauge. The extra capacitance should be negligible.

To correctly understand the impact of your cable runs we'd need to know the impedance curves of your speakers, but this is usually moot, even for ca. 30 foot runs.
commsysman's Avatar commsysman 09:39 AM 01-16-2013
0.2 ohms of wire resistance, when connected to a 4 ohm speaker, is 5% of the impedance of the speaker.

This simply means that you will have a 5% loss in the wire, and have to turn the volume up 5% higher. Big freaking deal...lol.

With a double run, or 14 gauge wire, you will knock the loss down to 2% or so.
segmentor's Avatar segmentor 05:23 PM 01-16-2013
Thanks guys.

Commsysman - yep but I'm also aware that the speaker will have a different impedance at different frequencies and although I can't find an impedance graph for the F/XiA4's I'm hoping the 8 ohm rating is close to the 'real' minimum.

Maybe this concept is overkill for 8 ohm speakers; I guess I will try it both ways and see if my ears can tell the difference.
commsysman's Avatar commsysman 05:28 PM 01-16-2013
I have looked at impedance graphs for hundreds of speakers, and they almost always have a minimum impedance of somewhere between 3 and 5 ohms, so I always go with the assumption of 4 ohms when considering wiring.

The average impedance is usually between 6 and 8 ohms over the whole frequency range, but the minimum needs to be considered too.
segmentor's Avatar segmentor 03:40 AM 01-17-2013
Thanks for the advice; I can't argue with the logic.
arnyk's Avatar arnyk 07:20 AM 01-17-2013
Quote:
Originally Posted by commsysman View Post

0.2 ohms of wire resistance, when connected to a 4 ohm speaker, is 5% of the impedance of the speaker.

This simply means that you will have a 5% loss in the wire, and have to turn the volume up 5% higher. Big freaking deal...lol.

With a double run, or 14 gauge wire, you will knock the loss down to 2% or so.

The problem with too-thin hifi speaker wires is not overall sound loss, but differential sound loss at various frequencies.

If the problem were due to overall sound loss, the too-thin cable could be compensated for over a wide range by simply turning up the volume a little more.

Most speakers, as is correctly pointed out in post 6 have a frequency range where their impedance is minimum, while the impedance of the same speaker is much higher over broad ranges at other frequencies.

The cable's resistance usually causes far more loss in the range of frequencies where the speaker's impedance is minimum or close to minimum. The cable's losses over the range where the speaker's impedance is higher is often much less.

The difference in the cable's loss in different frequency reanges is the essence of the problem. If the difference in the losses is large enough then the sound of the speaker may be audibly colored by the cable's excess resistance.

This same problem can be caused by certain tubed amplifiers that may provide even higher source impedances than the wire that we are talking about right now.

5% loss corresponds to a 0.5 dB loss which is possibly audible, but rarely if ever an actual serious sound quality problem. Modern AVRs with automated system optimization facilities may address problems like this or even far worse as part of their normal operation.

Therefore the basic advice that a speaker cable with only 0.2 ohms or less resistance will cause no serious problems with a reasonable worst case speaker that dips down to 4 ohms is basically good.

However I thought this was a good opportunity to clarify the basic goal of the discussion, which is to produce high fidelity and minimize audible coloration.
commsysman's Avatar commsysman 08:35 AM 01-17-2013
If you carefully analyze what you just said, you will realize that you are talking nonsense.

If speaker wire has a resistance of 0.2 ohms, which is much higher than most will be, that will give you a 5% loss at a frequency where the speaker is 4 ohms, and a 1 % loss at a frequency where the speaker is 20 ohms.

So....in one case the speaker is getting 95% of the power and in the second case it is getting 99%. Do you think anyone can hear a 4% change in volume between the two frequencies? Absolutely not!!

It is well-documented by extensive hearing research that no one can hear that kind of minute difference.

Quote:
Originally Posted by arnyk View Post

The problem with too-thin hifi speaker wires is not overall sound loss, but differential sound loss at various frequencies.
If the problem were due to overall sound loss, the too-thin cable could be compensated for over a wide range by simply turning up the volume a little more.
Most speakers, as is correctly pointed out in post 6 have a frequency range where their impedance is minimum, while the impedance of the same speaker is much higher over broad ranges at other frequencies.
The cable's resistance usually causes far more loss in the range of frequencies where the speaker's impedance is minimum or close to minimum. The cable's losses over the range where the speaker's impedance is higher is often much less.

The difference in the cable's loss in different frequency reanges is the essence of the problem. If the difference in the losses is large enough then the sound of the speaker may be audibly colored by the cable's excess resistance.

This same problem can be caused by certain tubed amplifiers that may provide even higher source impedances than the wire that we are talking about right now.

5% loss corresponds to a 0.5 dB loss which is possibly audible, but rarely if ever an actual serious sound quality problem. Modern AVRs with automated system optimization facilities may address problems like this or even far worse as part of their normal operation.

Therefore the basic advice that a speaker cable with only 0.2 ohms or less resistance will cause no serious problems with a reasonable worst case speaker that dips down to 4 ohms is basically good.

However I thought this was a good opportunity to clarify the basic goal of the discussion, which is to produce high fidelity and minimize audible coloration.

SAM64's Avatar SAM64 08:43 AM 01-17-2013
Quote:
If you carefully analyze what you just said, you will realize that you are talking nonsense.

This is hilarious...then he goes on to repeat his bad math, again....proving that he has absolutely no idea.
arnyk's Avatar arnyk 09:42 AM 01-17-2013
Quote:
Originally Posted by commsysman View Post

If you carefully analyze what you just said, you will realize that you are talking nonsense.

If speaker wire has a resistance of 0.2 ohms, which is much higher than most will be, that will give you a 5% loss at a frequency where the speaker is 4 ohms, and a 1 % loss at a frequency where the speaker is 20 ohms.

So....in one case the speaker is getting 95% of the power and in the second case it is getting 99%. Do you think anyone can hear a 4% change in volume between the two frequencies? Absolutely not!!

It is well-documented by extensive hearing research that no one can hear that kind of minute difference.

For reference, a 5% loss is about the same as a 0.5 dB loss. It is well-documented that under some conditions a 0.5 dB loss is audible. I've duplicated this test result myself under double-blind conditions.

However, something I wrote seems to be itself lost. I wrote:

"5% loss corresponds to a 0.5 dB loss which is possibly audible, but rarely if ever an actual serious sound quality problem."

I also wrote:

"Therefore the basic advice that a speaker cable with only 0.2 ohms or less resistance will cause no serious problems with a reasonable worst case speaker that dips down to 4 ohms is basically good."

In short, I agreed with the general point you made in your post.

So, you are arguing with yourself! ;-)
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