Is distance to speaker & impedance the only criteria when deciding speaker cable thickness/gauge?

gadgetluvr

Active Member
Hi all,

I'm fairly new to this "scene" but have done a fair bit of reading trying to get my head around all of this.

My query is this - do I need to factor anything else other than distance from my amplifier to the speaker and the impedance of the speaker before I decide what thickness speaker cable to use? For reference, my amp is the Denon AVR-X2700H and the speakers are the Wharfedale DX-2's (4Ω nominal impedance). I will be using 12 AWG cable for my rear speakers as they are about 45 feet each from the amp. However for the fronts and center I know I can use 20 AWG as they are only 5 feet runs - but should I? The amp is a new model - do I need to worry about the power it puts out as well? Or the fact that I will be running 20 AWG and 12 AWG cables at the same time?

I'd prefer to use the 20 AWG as I can't hide all of the cable and obviously the thinner the better for aesthetic purposes; and they are about half the cost although that's not a massive factor as they are short runs.

I've specifically used "AWG" and not "mm²" as I've sourced my cable from the U.S. It was surprisingly hard to source white 12 AWG cable (or equivalent) cable in the UK without paying a premium for it.
The closest to 12 AWG here is 4 mm² and the closest to 18/20 AWG is 0.75 mm² (QED Profile 42 is what I have my eyes on).

Many thanks in advance.
 
Last edited:

anden

Standard Member
Seems like you got the principles correct, however with overall a bit overdimensioned sizes. You could probably go all 1.5 mm² unless you really want to go thinner with the front speakers.

Speaker wire.jpg
 

gadgetluvr

Active Member
Thanks for the response. I hadn't quite seen your table of lengths before, the charts I came across

(links below) seemed to suggest that I'd need about 12 AWG for my 14-15m runs to each of my 4 Ω speakers. And yeah, if I can go 0.75 mm² for the fronts that would be ideal!



Speaker Wire 101: Which Is the Best Gauge for Your System? (also references Roger Russell which your chart also does)
 

Ormy

Member
Sometimes you also need to take into account the power you will be sending the speakers, obviously if the power is several hundred watts or more you'll need thicker wire than what the various charts posted so far show. But in your case your amp can't do much more than 100W to each channel so you're fine.

Here's the chart I use for quick reference.
speakr_gauge_help.jpg


If you need more detailed info you can use the following chart and the rule of thumb that as long as the wire resistance is less than 2% (some say 5%) of the speaker impedance then you're good.
CHART-1-w-1024x1024.jpg


In your case, 20awg has 10.15 ohms per 1000ft as per this chart. 5ft is 1/200 of 1000ft, 10.15/200=0.05075ohm. (0.05075/4)*100=1.2% so it should work just fine.
 
Last edited:

gadgetluvr

Active Member
Sometimes you also need to take into account the power you will be sending the speakers, obviously if the power is several hundred watts or more you'll need thicker wire than what the various charts posted so far show. But in your case your amp can't do much more than 100W to each channel so you're fine.

Here's the chart I use for quick reference.
speakr_gauge_help.jpg


If you need more detailed info you can use the following chart and the rule of thumb that as long as the wire resistance is less than 2% (some say 5%) of the speaker impedance then you're good.
CHART-1-w-1024x1024.jpg


In your case, 20awg has 10.15 ohms per 1000ft as per this chart. 5ft is 1/200 of 1000ft, 10.15/200=0.05075ohm. (0.05075/4)*100=1.2% so it should work just fine.

Thanks, that's useful info and not something I've come across previously. In your first chart, would you happen to have figures for <8 feet runs with 4 Ω speakers by any chance please?

If I've calculated correctly based on your second chart, even a 10 ft. run works out to 2.5% (?) which I'm ok with.

I think what threw me was in the chart at the link below, even using 18 AWG cable they worked out only a 5 ft. run for a 4 Ω speaker and I still can't work out why.

 

Ormy

Member
Thanks, that's useful info and not something I've come across previously. In your first chart, would you happen to have figures for <8 feet runs with 4 Ω speakers by any chance please?

If I've calculated correctly based on your second chart, even a 10 ft. run works out to 2.5% (?) which I'm ok with.

Sorry I don't, in this case just use the second chart exactly as you have, and your calculations are correct.

I think what threw me was in the chart at the link below, even using 18 AWG cable they worked out only a 5 ft. run for a 4 Ω speaker and I still can't work out why.


I'm not sure but I guess they are just adding a margin of error incase the situation requires more power than usual for domestic settings.
 

gadgetluvr

Active Member
Sorry I don't, in this case just use the second chart exactly as you have, and your calculations are correct.
No problem, and many thanks for validating my calcs. My amp specs do say 150w/channel and hence my request, just to be sure I was taking that factor into account as well.
 

Ormy

Member
My amp specs do say 150w/channel

Careful with AVR specs, I bet that's measured with only 2 channels driven which is common practice. See if they give an 'all channels driven' figure.

Or just look up the max power consumption of the PSU in the electrical specs. It says 500W here. So if you have 5 speakers playing it's just not possible for the amp to sustain more than 100W to each of 5 speakers.
 

gadgetluvr

Active Member
Careful with AVR specs, I bet that's measured with only 2 channels driven which is common practice. See if they give an 'all channels driven' figure.

Or just look up the max power consumption of the PSU in the electrical specs. It says 500W here. So if you have 5 speakers playing it's just not possible for the amp to sustain more than 100W to each of 5 speakers.
Thanks, I wasn't aware that that's how it worked. So, if at some point, I find myself running a 2.0 system instead of my 5.1 I will need to be wary with my 20 AWG speaker cable then as the amp specs state 125 W (6 Ω, 2 ch.)?
Sorry about the silly questions .. I'd like to try and get it right the first time as a lot of my cable will be concealed once installed.
 

Ormy

Member
Thanks, I wasn't aware that that's how it worked. So, if at some point, I find myself running a 2.0 system instead of my 5.1 I will need to be wary with my 20 AWG speaker cable then as the amp specs state 125 W (6 Ω, 2 ch.)?

If the lengths are only 5ft you should be fine. Hard to say though, the Wharfedale DX2 speakers you mentioned in your first post have quite a low sensitivity (only 86dB 2.83v/1m) which means they require a lot of power to get loud. If you want to err on the side of caution go with 18 or 16 awg instead.
 

anden

Standard Member
Sometimes you also need to take into account the power you will be sending the speakers, obviously if the power is several hundred watts or more you'll need thicker wire than what the various charts posted so far show.
Why would that be the case, I am curious? A 1.5 mm² (~16 AWG) cable, for instance, can handle several thousands of continuous watts, very much more than you ever transfer with music.
 

gadgetluvr

Active Member
the Wharfedale DX2 speakers you mentioned in your first post have quite a low sensitivity (only 86dB 2.83v/1m) which means they require a lot of power to get loud.
Thanks again. I'm starting to wonder whether I should return these speakers now considering I haven't opened them yet. It's a shame none of the rather glowing reviews it seems to receive mention practical points such as this ...
 

Ormy

Member
Why would that be the case, I am curious? A 1.5 mm² (~16 AWG) cable, for instance, can handle several thousands of continuous watts, very much more than you ever transfer with music.

I'm admittedly simplifying things for this particular context by saying more power requires thicker cable. In terms of general electricity that isn't true, the limiting factor is the current in the cable. If you use a crazy high voltage you can transmit lots and lots of power through a thin cable, that's how the national grid works (and long distance electricity transmission in every country).

But domestic speakers nearly always fall in the 2-8ohm impedance range, which limits the maximum voltage they will typically be sent from domestic amplifiers (tannoy systems in contrast use much higher voltages and higher impedance coils in order to get away with very long cable lengths to get all around a stadium), therefore in home audio, generally speaking, higher power requires higher current.

Current in wires causes heating proportional to the square of the current. There's little danger of starting a fire (although not impossible if you actually tried, similar principle to 9v battery + iron wool scenario). However heating the wire increases its resistance, and if its resistance was already close to the threshold of audibility when the wire was at room temperature... Keep in mind that all of these charts assume the wire is at room temperature.

Besides all that, I can tell you from experience (and I can show you the calculations if you like), if you try to push 2000W continuous to a 2ohm speaker (of average to low sensitivity) through only a 5ft run of 16awg wire it's going to work but the wire gets warm to the touch after a while, approx 40W of heat dissipated into the wire. If the speaker is 8ohm then it's not so bad. If the wire is longer there will be even more heating.
 
Last edited:

anden

Standard Member
Interesting thought. However, there is no support for speaker wire heating to be a potential issue in any of the references listed in this thread, and not in any other source on home audio that I have seen either.

And when I now out of curiousity did a quick check of conductor temperature rise as a function of conductor area and amperage, it suggests a negligible effect indeed. The most powerful AVR or receiver could only raise wire temperature a couple of °C, even if run continuously on max power, connected to a 4 Ω speaker via an 18 AWG or 0.75 mm² wire. Even a massive 600 W separate amp playing continuously on flat out max power and hooked up to a 4 Ω speaker via a 15 AWG or 1.5 mm² wire, wouldn't raise wire temperature more than about 10 °C at most, and much less in real usage.

So for home audio, wire heating and wire selection based on amp power seem to have relevance only in theoretical exercise, which I assume is why it doesn't seem to be mentioned anywhere.
 

gadgetluvr

Active Member
So for home audio, wire heating and wire selection based on amp power seem to have relevance only in theoretical exercise, which I assume is why it doesn't seem to be mentioned anywhere
From the various material I have read I tend to agree. I'm not denying there will be a temperature rise but unless in real extreme (stupid?) circumstances you should be able to discount temperature as a variable.
 

Ormy

Member
Interesting thought. However, there is no support for speaker wire heating to be a potential issue in any of the references listed in this thread, and not in any other source on home audio that I have seen either.

And when I now out of curiousity did a quick check of conductor temperature rise as a function of conductor area and amperage, it suggests a negligible effect indeed. The most powerful AVR or receiver could only raise wire temperature a couple of °C, even if run continuously on max power, connected to a 4 Ω speaker via an 18 AWG or 0.75 mm² wire. Even a massive 600 W separate amp playing continuously on flat out max power and hooked up to a 4 Ω speaker via a 15 AWG or 1.5 mm² wire, wouldn't raise wire temperature more than about 10 °C at most, and much less in real usage.

So for home audio, wire heating and wire selection based on amp power seem to have relevance only in theoretical exercise, which I assume is why it doesn't seem to be mentioned anywhere.

Yeah exactly, the effect is pretty negligible unless you're pushing thousands of watts or are using stupidly thin wire. I just wanted to add the info for completeness and as a caution of what could happen if the wire is too thin.

E.g. if some cheapskate were to use a long run of the 18AWG wire from your first example with the 600W separates amp from your second example (along with low impedance, low sensitivity speakers) then the heating would start to cause issues with sound quality.
 
Last edited:

The latest video from AVForums

AVForums Movies Podcast: We review Dune and ask which is the best decade for horror movies?
Subscribe to our YouTube channel

Full fat HDMI teeshirts

Support AVForums with Patreon

Top Bottom