Speaker cable thickness and OFC vs CCA

Stu C

Active Member
This is my first post, though I've often quietly followed a number of threads here. I am hesitant to start another thread on speaker cable, but following my recent purchase experience, I have been giving thought to cable specs, and I felt that some advice on here does not make sense to me, so...

Following a number of posts in these forums recommending cheap speaker cable from ebay/Amazon, I took the plunge to save some cash, safe in the knowledge that copper is copper... unless it is not copper (I know, some will say that I should have seen it coming). Anyway, I purchased 20m of this cable:

322 Strand Flexible 2.5mm² Professional Transparent HiFi Loud Speaker Cable from The One Stop Sat Shop

It is advertised as "oxygen free copper", and there is no mention of aluminium or CCA; however, while it has a nice copper appearance from the outside, the core looks very silver and shiny! So, I feel conned... but I'll come back to this.

I passed the cable to an electrician at work, who came back reporting 0.3 ohm resistance (he may have done some number rounding). Looking here and here, copper and aluminium
are 0.134 and 0.212 ohm, respectively, for 20m of 2.5mm² cable... unless my source of information is flawed, I clearly do not have OFC cable!

I have read many posts on here in which the following advice has been given:
- use better cable for the front speakers and cheaper cable for the surround speakers
- always use at least 2.5mm² cable
- always use OFC, never use CCA

I buy into the logic that all "pure" OFC cables are equal, so I see "better" cable as meaning thicker gauge; however, front speakers are typically closer to the amp than surround speakers, so I think that the thicker, "better" cable should be saved for the surrounds, and "cheaper" cable used for the front speakers, provided they are of appropriate gauge... does this make sense?

Always use 2.5mm²... I'm assuming Roger Russell is correct in his details, therefore, with a typical 8 ohm speaker, 2.5mm² copper cable (~ 13 AWG) is suitable for ~30m run... that's a big living room! Why ever use this for front speakers with a 1 or 2m run??? 1.5mm² is suitable for a 20m run, and 0.75mm² is suitable for a 10m run. Agreed?

Considering the CCA cable that I have right now, 0.015 ohm/m does not compare well to 0.0067 ohm/m for copper, or even 0.0106 ohm/m for aluminium, at 2.5mm². I need a 10m run for my 8 ohm speakers... 10 x 0.015 = 0.150 ohm wire resistance, which is less than 2% of the speaker impedance... fit for purpose? I estimate that this 2.5mm² CCA cable is equivalent to 1.12mm² OFC cable, which according to Roger Russell, should be suitable for ~ 15m run.

Based on my calculations, 2.5mm² CCA cable should be more than capable for a 10m run; which explains why so many people of the forum are happy with this cable. However, do I keep it or send it back? Even though it is fit for purpose, I feel that it was falsely advertised, which makes me want to kick up a fuss and send it back; in which case, I may spend a few extra quid on 1.5mm² Van Damme Blue cable (but not 2.5mm²!!!).

I hope you've managed to wade through all that, and I would appreciate thoughts and discussion.
 

Trollslayer

Distinguished Member
Looking at the advert it doesn't mention the material the conductor is made from.
 

Stu C

Active Member
In the product description:

Lets have a look at the specification of this cable: Cable size - 2 x 2.5mm squared Conductor - 322 x 0.1mm Conductor type - oxygen free copper Cable overall dimensions - 3.6mm x 7.5mm Polarisation - one core has a blue stripe This speaker cable is transparent in line with modern styles of speaker cable and it is extremely tough and durable.
 

dogfonos

Well-known Member
You raise some interesting and contentious points. I'm only going to tackle your first point though...

Without wishing to cast doubt on the competency of the electrician who measured the resistance of the speaker cable, did he have the equipment required to get an accurate and repeatable measurement at these low resistance values? His instrument may have been more of a 'general purpose' meter in which case it's possible (likely?) it won't give meaningful results. The 0.3 Ohms figure he obtained may not have been rounded but may simply represent the figure displayed on the meter due to it's low resolution (i.e. unsuitability) at these values. Also, is the meter calibrated/validated and was it zero'd or checked in any way immediately prior to the measurement? If not, it's anybody's guess as to the meter's accuracy. And then there's the issue of the integrity of the connection between the meter and the test wire - connection security makes a difference at these values.

The rest of the points you make are just about all based on this original resistance measurement. IMO, it would be best to check the validity of the initial measurement before drawing too many conclusions. That's not to say you're wrong though...
 

Stu C

Active Member
@dogfonos, thanks for the input. I'll ask tomorrow regarding equipment and sensitivity. We didn't have reference resistance values to hand earlier today, so I wasn't sure about range and accuracy.

In addition to my plight with questionable speaker cable, I am also keen to raise questions on the general recommendations regarding front vs surround cabling, "always use at least 2.5mm² cable", and whether CCA is ever acceptable.
 

BlueWizard

Distinguished Member
CCA is Copper Clad Aluminum. If you need wire on the cheap and distances are short, this is fine. But I don't think anyone would consider it true Hi-Fi cable.

For true Hi-Fi the preferred cable is OFC or Oxygen Free Copper. Removing the Oxygen tends to remove impurities from the copper. so OFC indicates, among other things, a higher purity of copper.

As far as the size, that is more difficult, some say the speaker cable can not exceed 2% to perhaps 5% of the Nominal Speaker Rating. B&W, rather than a percent, simply says speaker wire can not exceed 0.1 ohms.

For Euro size wires (1.5mm² and 2.5mm²) you can't find specification charts, but you can find them for AWG (American Wire Gauge) wire -

American wire gauge - Wikipedia, the free encyclopedia

The closest equivalents are 13ga at 2.62mm² and 15ga at 1.65mm².

For 13ga/2.62mm², the resistance per 1000 meters is 6.57 ohms. For 1000 feet it is 2.003 ohms.

For 15ga/1.65mm², the resistance is 10.45 per 1km and 3.18 for 1000 feet.

For 17ga/1.07mm², the resistance is 16.61 per km and 5.96 for 1000 feet.

Using standard 13ga we have the following resistance per distance - 6.57/1000m, 0.657/100m, 0.0657/10m, and 0.00657/1m

So a typical 3 meter (10 foot) wire is (0.00657x3=) 0.0197 ohms. Very low and well below all standard requirements. (0.0197/4ohms =) 0.5%. Remembering that we are trying to say under 2%. For an 8 ohm speaker, that is actually 0.25%.

The worst wire, 17ga/1.07mm² would be 16.61/1000m, 1.661/100m, 0.1661/10m, and 0.01661/1m. Times 3 meters is (0.01661x3=) 0.04983. Still low.

For a 4 ohm speaker, the resistance would be (0.04983/4 = ) 1.25%. Again acceptable. For an 8 ohm speaker, the resistance would be 0.623% of the nominal impedance. Still very good.

However, 2.5mm² speaker wire is very affordable, easy to work with, and gives you huge reserves of power handling capability.

For short runs with normal amp power, 1.5mm² is probably fine.

In a vast majority of circumstances 4.00mm² wire is massive overkill, and very thick, hard to get into the terminals.

In the end, 1.5mm² and the preferred 2.50mm² cover the needs of a vast majority of people.

Steve/bluewizard
 

BlueWizard

Distinguished Member
Generally, the longest recommended run for any speaker wire is 50 feet (15.25meters). Once you exceed that distance it becomes more about the limitations of capacitance and inductance, than the simple resistance of the wire.

Now, you have to do what you have to do.

But generally these are the limitations.

- Resistance no greater than 2% of the nominal impedance of the speaker and preferably less
- distances not to exceed 50ft or 15 meters

You will find a chart here that gives working distances to various speaker loads for various size wires. There is another chart like this somewhere else, but I can't find it right now -

Speaker wire - Wikipedia, the free encyclopedia

Notice once the lengths exceed 50 feet they are STARRED (asterisk) as not recommended.

Steve/bluewizard.
 

Stu C

Active Member
@Steve, thanks for the vast amount of info; though it feels more like you have done a copy/paste info dump rather than responding to my post.

You imply that CCA is inferior quality, however, you also say that the speaker cable can not exceed 2% to perhaps 5% of the Nominal Speaker Rating - the CCA cable that I described meets this requirement.

You mention "true Hi-Fi cable"... what exactly is the definition? If cable is of suitable conductance/resistance for the setup, does it matter if it is CCA, OFC or ETP copper? I certainly don't think the 0.05% purity difference between OFC and ETP will make any real difference; but I am interested to hear differing opinions.

For a 10m run, I am suggesting that 0.75mm² OFC should be suitable, whereas you appear to suggest 2.5mm², which, for Van Damm Blue cables, is double the price; and for a 20m run, 2.5mm² is 50% more expensive than 1.5mm². Why spend the extra money? What is gained from having "huge reserves of power handling capability"?

I'm being very direct with my questions because I am keen to discuss, not to be argumentative, so please don't take offence. :)
 

BlueWizard

Distinguished Member
Regarding CCA wire, I said -

"If you need wire on the cheap and distances are short, this is fine."

But if you can afford it, there is no reason not to get OFC wire.

As to the 2% resistance, that is a general guideline. Also, B&W says 0.1 ohms. Use either as a guideline. However, it would be unwise to take it right to the edge.

Keep in mind my goal is not to tell you what to do, but to give you the information necessary to make your won informed decistion. You can do any thing you want. You can use wire coat hangers ... if you want. But realistically we try to stay within reasonable bound of functionality.

The closest AWG wire to 0.75mm² are -

18ga = 0.823mm² which is 20.95 ohms per 1 kilometer.

19ga = 0.653mm² which is 26.42 ohms per kilometer.

18ga is closest. The resistance per distance is easy enough to determine -

20.95 per 1000 meter
2.095 per 100 meter
0.2095 per 10 meter
0.02095 per 1 meter

Using your 10 meter example, we have exceeded the Bowers-Wilkins recommendation of 0.1 ohms maximum. To a 4 ohm speaker 10 meters of 0.823mm² is 5.24%. To an 8 ohm speaker 10 meters is 2.62%. Both those are in excess of the recommended 2% maximum.

Will that work, yes. Will that work well, probably not. But it will work. Depending on how you define 'work'.

Now, I worked with a few bands, and I've seen people use low signal level guitar cables for PA speaker cables. Did that work? Yes, in the sense that sound came out of the speaker. But is that all you demand? That sound come out? Or would you like that sound to sound good.

As I said, you can do anything you want. You can string together ear phone wires, and yes it will work, but no it wouldn't sound good.

If you look at most sites selling speaker wires, you will see that they are dominated by 1.5mm², 2.5mm², and though more rare 4.00mm². Many sites selling wire by gauge rather than cross sectional area, the most common are 16ga (1.31mm²) and 14ga (2.04mm²). My current wires are OFC 14ga.

For short runs, you can certainly use 18ga/19ga wire. I've done it many times, but for 10 feet not for 10 meters.

Back to CCA, fine if that's what you want, and if all other parameters fall into place, fine ... do what you want. But, Copper has a higher conductivity than aluminum. Which as you point out means more aluminum relative to a given amount of copper. Lots of people buying wire on the cheap do this. Though most do it not knowing what CCA is. It is copper clad, it looks like copper ... close enough.

Why buy more aluminum, when less copper will do the job? The only reason is that you are on a starvation budget and can't afford copper. That's OK, we've all been there. But, OFC copper wire is not crazy expensive. You don't need fancy double insulated Van Damme Blue 2.5mm. In my case, I have straight forward twin-lead single insulated rope-braid OFC copper of 14ga with runs of about 6 feet to 8 feet each. (note: I have two pair of speakers in a Stereo system)

i65-spade1as-jpg.302793


I showed you the math in my first post so that you could work this out on your own. There isn't anything I've said that can't be resolved with a little common sense, access to the 'Net, and a basic calculator.

For 10 feet or less, 0.75mm² is probably fine. But as you can see from the math, for 10 meters, by no standard is 0.75mm² fine.

The problem shakes out the same for CCA wire. What does it cost? What is the resistance per distance? If the math and price work out for you, then fine. And if not ... then not.

As I said, I've used 18ga wire (0.823mm²) many times with great success, but never for 10 meters. Typically for 10 to 15 feet.

There are places that sell OFC wire in bulk for deeply discounted prices. This isn't much different that what I use. If you are on the cheap, consider these -

Cabling4Less - Speaker Cables and Adaptors

25m of 2.5mm² CCA is about £18.

25m of 2.5mm² OFC is about £29.

Yes, OFC is more money, but seriously, you can't scrape together £30?

I've not done business with Cabling4Less, I just stumbled across their website and remembered they sold bulk wire. But there are countless places like this that also sell bulk wire, you just need to search them out.

No one here is likely to give you a definitive "Do this", we present you with the information, the general consensus, and provide you with the necessary background information, then you have to make your own decision.

Happy to help, assuming I'm actually helping.

Steve/bluewizard
 
Last edited:

BlueWizard

Distinguished Member
The detailed description of the wire advert says -

"Cable size - 2 x 2.5mm squared Conductor - 322 x 0.1mm Conductor type - oxygen free copper Cable"

Keep in mind anytime you cut a wire, the cut is going to be shiny. As to the resistance measurement from your friend, unless he had an exceptionally accurate meter, tiny resistances like this are not going to be very accurate. I wouldn't put too much stock in that measurement.

I think you are fine. With 2.5mm² of what is advertised as OFC, you should be fine. Even if it is not OFC, you will still be fine. The power demands on the Surround speakers are much lower than the front. which is why people say it is wise to put your best wire on the front, and lesser wire to the rear. But lesser wire to the rear doesn't mean bad wire to the rear.

In all honesty, I don't think you have a problem.

Steve/bluewizard
 

Alan Mac

Well-known Member
I passed the cable to an electrician at work, who came back reporting 0.3 ohm resistance. Looking here and here, copper and aluminium
are 0.134 and 0.212 ohm, respectively, for 20m of 2.5mm² cable...

The total DC resistance of the conductor in a 20 m length of 2-core cable with a 2.5 mm² cross sectional area per conductor of pure copper, is 268 milli-ohms (not 134 milli-ohms).


Alan
 

MemX

Well-known Member
The total DC resistance of the conductor in a 20 m length of 2-core cable with a 2.5 mm² cross sectional area per conductor of pure copper, is 268 milli-ohms (not 134 milli-ohms).


Alan
Thanks as always, Alan :)

Assuming there was some rounding involved in the measurement process, 0.3 ohm would therefore be about right??
 

BlueWizard

Distinguished Member
The total DC resistance of the conductor in a 20 m length of 2-core cable with a 2.5 mm² cross sectional area per conductor of pure copper, is 268 milli-ohms (not 134 milli-ohms).


Alan

Alan, you are always a deep well of technical knowledge, but I have to ask, where did you get this number (268 milli-ohms)?

According to the AWG specification chart I used, 2.62mm² is 6.57 ohms per kilometer, so 0.0657 ohms per 10 meters or 0.1314 ohms per 20 meters.

Did you measure or do you have access to Euro Cross Sectional Area Wire Spec charts? If you do have access to wire spec charts on-line, could you give me a link. I've been searching high and low to find one, and have come up dry every time.

I don't think a typical Volt/Ohm meter is going to be very accurate at tiny resistances like this. There might be some precision meters capable of accurately measuring this small, but they are going to be very expensive.

Not issuing a challenge here, just trying to satisfy my curiosity.

Thanks again for you never ending fountain of knowledge.

EDITED: it just occurred to me that you specifically said 20 meter of 2 CORE 2.5mm² cabling. If you meant 20 meters out and 20 meters back, then, yes, the total by my calculation is 0.263 ohms. Though I'm calculating using 2.62mm² wire.

Still, if you know of an on-line wire spec chart for cross sectional area wire, I would love to have a link.

Steve/bluewizard
 
Last edited:

Alan Mac

Well-known Member
Alan, where did you get this number (268 milli-ohms)?

According to the AWG specification chart I used, 2.62mm² is 6.57 ohms per kilometer, so 0.0657 ohms per 10 meters or 0.1314 ohms per 20 meters.

Did you measure or do you have access to Euro Cross Sectional Area Wire Spec charts? If you do have access to wire spec charts on-line, could you give me a link. I've been searching high and low to find one, and have come up dry every time.

I don't think a typical Volt/Ohm meter is going to be very accurate at tiny resistances like this. There might be some precision meters capable of accurately measuring this small, but they are going to be very expensive.
Steve/bluewizard


In a 20 m long loudspeaker cable, the total conductor length is 40 m (not 20 m). The resistance of 40 m of 2.5 mm² CSA copper wire is 268 milli-ohms at room temperature (293 K).


Here is a cable resistance calculator which may be useful
ePanorama.net | Audio | Video | Circuits | Electronics Design


For measurement of low DC resistance I use:
a Rhopoint M210 Milliohm meter.
M210 Milliohm Meter | Rhopoint Instruments

and a TTi BS407 Precision Milli/micro ohmmeter
Description and Specifications for the BS407 micro ohmmeter from TTi


For AC resistance (the Real part of the complex impedance) at frequencies up to 100 kHz, I use an Agilent U1733C LCR auto-bridge.


Alan
 

The latest video from AVForums

Are the TCL MiniLED TVs better than OLED? TCL Interview with Marek Maciejewski | AVForums Podcast
Subscribe to our YouTube channel

Full fat HDMI teeshirts

Support AVForums with Patreon

Top Bottom