REVIEW INCL. Just got monoprice speaker wire in.....why do you guys reccomend this so much? - Page 9 - AVS Forum | Home Theater Discussions And Reviews
Forum Jump: 
 41Likes
Reply
 
Thread Tools
post #241 of 372 Old 03-19-2014, 01:50 PM
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,829
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1334 Post(s)
Liked: 750
Quote:
Originally Posted by Ratman View Post

I thought that the intention was to "prove" Monoprice 12AWG is not 12AWG.
That would presuppose an outcome and corrupt the experiment. But yes, the original purpose was to compare the two cables that OP mentioned. But then this was suggested:
Quote:
Originally Posted by mcnarus View Post

If someone's going to do this, they need to do it right. First, you need multiple samples. The fact that you've got a foot of AWG 12 that measures like AWG 13 doesn't prove anything except you got a bad sample. Second, you need to compare it to others in the industry: Lowes, HD, BJC, Belden, whatever Parts Express sells. "Everybody does it" is a weak defense, but it's a defense.

So the insanity set in to actually go and buy a number of cables to see if there is a practice of under delivering, how common that is.
Quote:
With the proper equipment and tools, that should have been easily accomplished once Amirm had the wire. Now it's turned into.......... dodgeball.
Well, you or anyone else can go and do the test if you want it done differently. I want to make sure the results are repeatable and as defensible as they can be. There are a lot of barriers here which I won't go into here but will when I publish my report. I have run multiple tests already, refining the methodology due to these factors. I am going to re-run the tests again in a new way as to minimize the error and if that works, then I will be ready to post them.
amirm is offline  
Sponsored Links
Advertisement
 
post #243 of 372 Old 03-19-2014, 07:53 PM
AVS Forum Addicted Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 12,343
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3276 Post(s)
Liked: 3363
Testing milli-ohm resistance accurately, precisely, and with good repeatability is a daunting task. I can wait, especially considering the pay involved... smile.gif

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
Sponsored Links
Advertisement
 
post #244 of 372 Old 03-20-2014, 04:48 AM
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,420
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 851 Post(s)
Liked: 1251
Quote:
Originally Posted by DonH50 View Post

Testing milli-ohm resistance accurately, precisely, and with good repeatability is a daunting task. I can wait, especially considering the pay involved... smile.gif


The key to this sort of measurement is using a 4 terminal measurement technique which I believe you mentioned a few days ago.

Just to clarify for other readers:

http://en.wikipedia.org/wiki/Four-terminal_sensing



As the picture shows, current is applied to to the test jig at the two points most distant from the device under test ( A & D) , and the quantity measured (usually voltage) is measured at the two near points (B & C). The device being tested is R.

The current used in the test is supplied by stable voltage source E and measured with voltage measurement device V. Resistor Rl is used to control the current flowing through the device under test R.

There are usually some spurious voltages assocated with the contact between the current source and the device under test at A and D, but since they are outside the measurement loop B & C they do not enter the actual data that is measured with measurement device V.
arnyk is offline  
post #245 of 372 Old 03-20-2014, 06:35 AM
AVS Forum Special Member
 
AV Doogie's Avatar
 
Join Date: Jan 2005
Location: Rockford, IL
Posts: 2,328
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Liked: 34
Quote:
Originally Posted by DonH50 View Post

Testing milli-ohm resistance accurately, precisely, and with good repeatability is a daunting task. I can wait, especially considering the pay involved... smile.gif

I use a Megger DLRO unit to perform contact resistance measurements on electrical protective equipment (Circuit breakers, disconnects, etc.). Whether using the 10A or 100A version of these devices, the contact resistance measurements can be accurate to a few micro-ohms with a calibrated instrument. The problem here is how do you take the measurement without adding a substantial amount of resistance by installing connectors at the wire ends for testing purposes. The mechanical interface of the connector can add resistance magnitudes close to the wire measurement.

My Home Theater Site:

https://imageshack.com/a/dPJl/1
AV Doogie is offline  
post #246 of 372 Old 03-20-2014, 06:54 AM
AVS Forum Addicted Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 12,343
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3276 Post(s)
Liked: 3363
I am painfully familiar with four-point Kelvin and micro-xxx (ohm, volt, amp, etc.) measurements. As has been said connection to the wires is always an issue. In Arny's picture the nodes at B and C are critical; any displacement of force and sense probe points can lead to errors. And of course the run from those nodes to the actual DUT (device under test) is not compensated. The other issue I have run into is noise that can corrupt the readings. Last time I measured ultra-low things (admittedly worse than this) I was in a screen room or built a special screen box to help isolate the fixture. I was using some older test gear, a leaf fA meter for some current measurements, and an Agilent DMM (3458A) for voltage and resistance, taking advantage of its four-point measurement and extensive processing features to reduce the impact of noise. I am sure Amir is using Kelvin probing but it is still non-trivial. I am sure there are newer, easier ways now; that was about 3 or 4 years ago. Or maybe I am just stupid, hard to tell sometimes. Measuring wires, at least at DC, is not something I have often done. My experience is based upon components (not audio, though most had to go to DC).

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #247 of 372 Old 03-20-2014, 07:01 AM
AVS Forum Special Member
 
Frank Derks's Avatar
 
Join Date: Jul 2002
Location: Region A,B,C
Posts: 2,487
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 539 Post(s)
Liked: 413
Any resistance added by connecting the measuring leads at B and C is insignificant in comparison to the voltmeters input impedance.

The wire under test can also be soldered together at the far end giving twice the length to be measured. (Don't know if this is already taken care of.)

Stereo is simply Multichannel light.
Frank Derks is offline  
post #248 of 372 Old 03-20-2014, 07:16 AM
AVS Forum Addicted Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 12,343
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3276 Post(s)
Liked: 3363
The concern is if force and sense contacts at B and C are not at the same point (so sense and force placement are not identical). We have customers putting the sense connection in the wrong place all the time then wondering why the voltage is off... I agree it is a minor concern for this particular case.

Not sure the input impedance of Amir's setup. I think the 3458A's DC input is very high, >10 G ohms, but 10 M ohms is not uncommon for run-of-the-mill meters. Neither is likely to be a significant error source.

In any event I'll bow to you experts.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #249 of 372 Old 03-20-2014, 07:48 AM
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,420
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 851 Post(s)
Liked: 1251
Quote:
Originally Posted by Frank Derks View Post

Any resistance added by connecting the measuring leads at B and C is insignificant in comparison to the voltmeters input impedance.

Agreed and that is the beauty of the system.



The meter that is connected between B & C can easily cause an additional current drain that is actually down, down, down in the microamp range if you use a DVM, while the wire under test may be carrying a test current that is involves thousands of amperes of electrical current.

I usually use one of my 250 watt 8 ohm non-inductive low temperature coefficient bench test resistors for Rl. Any old DC power supply or low powered audio power amp can drive the test jig up to 1 amp or more test current.

The inaccuracy in the measurement is reduced by the ratio between the test current and the metering current, a ratio that can easily be a million to one. Any contact resistances at B & C have effects that are proportionately reduced.
Quote:
The wire under test can also be soldered together at the far end giving twice the length to be measured. (Don't know if this is already taken care of.)

Good point. For the purposes of testing all of the connections can be soldered for even greater accuracy and stability.
arnyk is offline  
post #250 of 372 Old 03-20-2014, 08:40 AM
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,829
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1334 Post(s)
Liked: 750
Quote:
Originally Posted by DonH50 View Post

The concern is if force and sense contacts at B and C are not at the same point (so sense and force placement are not identical). We have customers putting the sense connection in the wrong place all the time then wondering why the voltage is off... I agree it is a minor concern for this particular case.

Not sure the input impedance of Amir's setup. I think the 3458A's DC input is very high, >10 G ohms, but 10 M ohms is not uncommon for run-of-the-mill meters. Neither is likely to be a significant error source.

In any event I'll bow to you experts.
Your expertise is much appreciated Don smile.gif. You are right on all points. I have a meter that has a dedicated milliohm measurement. It is not a normal meter with four probes. The standard meters supply very small current and rely on very high accuracy A/D converters to show milliohms. My meter uses 200X more current so it creates a much more reliable situation where we are not relying on very small signals. But because it can measure down to 0.1 milliohms (0.00001 ohm), it can obviously measure many things including the resistance between its probes and wire. After all, one of the uses of such a meter is to measure such connections. There are also stability issues over time and from time to time. So variations are there and cannot be eliminated in such ad-hoc testing. The theoretical discussions around 4-probe/Kelvin measurements are just that: theoretical. Practical devices don't work in idealistic manners. And at any rate, I am utilizing that system and problems remain.

That said, I think I have useful data out of the tests that I ran last night. At least good enough to convey some needed data to the conversation. I will write up the description and post it soon.
amirm is offline  
post #251 of 372 Old 03-20-2014, 10:27 AM
AVS Forum Addicted Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 12,343
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3276 Post(s)
Liked: 3363
Thanks Amir.

I'd forgotten about the high-current systems, not something I have used much. A good way to gain range and precision when testing big wires or power contacts; not so good for GHz semiconductors... smile.gif I could not use amps, let alone 10's or 100's of amps. Most measurements were at mA currents. Different situation.

At micro-ohm levels temperature variation is a significant concern, at least when I last did something like this. Wire R tempcos are large... And oxidation was a major PITA. We chem-cleaned and measured in a dry nitrogen environmental chamber, not a complete panacea but helped a lot. Not something most hobbyists have sitting around... smile.gif

Picky typo: 0.1 m-ohm = 0.0001 ohms (think you added a zero).

This strikes me as the type of thing jneutron would love.

Whatever - Don

p.s. For the stuff I was doing soldering was not an option for a variety of reasons (among them unknown solder connection impedance and variation, contamination, and just no good way to solder to the DUT). Might be a reasonable thing to try here, except it seems like you already have enough range and resolution for your wires (?)

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #252 of 372 Old 03-20-2014, 10:56 AM
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,829
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1334 Post(s)
Liked: 750
Quote:
Originally Posted by DonH50 View Post

p.s. For the stuff I was doing soldering was not an option for a variety of reasons (among them unknown solder connection impedance and variation, contamination, and just no good way to solder to the DUT). Might be a reasonable thing to try here, except it seems like you already have enough range and resolution for your wires (?)
I considered soldering but then thought that few people use solder to terminate their connection. So instead, I twist the bare wires and add clamping force to it. I tested the reliability of that by putting additional pressure on the clamp and it made very little difference. My thought is that this is similar force to non-solder type compression fittings for speaker terminals or screwing in bare wires. Or at least good enough for government work. biggrin.gif
amirm is offline  
post #253 of 372 Old 03-20-2014, 11:00 AM
AVS Forum Addicted Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 12,343
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3276 Post(s)
Liked: 3363
Seems reasonable.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #254 of 372 Old 03-20-2014, 11:33 AM
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,420
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 851 Post(s)
Liked: 1251
Quote:
Originally Posted by DonH50 View Post

Thanks Amir.

I'd forgotten about the high-current systems, not something I have used much. A good way to gain range and precision when testing big wires or power contacts; not so good for GHz semiconductors... smile.gif I could not use amps, let alone 10's or 100's of amps. Most measurements were at mA currents. Different situation.

At micro-ohm levels temperature variation is a significant concern, at least when I last did something like this. Wire R tempcos are large... And oxidation was a major PITA. We chem-cleaned and measured in a dry nitrogen environmental chamber, not a complete panacea but helped a lot. Not something most hobbyists have sitting around... smile.gif

Picky typo: 0.1 m-ohm = 0.0001 ohms (think you added a zero).

This strikes me as the type of thing jneutron would love.

Whatever - Don

p.s. For the stuff I was doing soldering was not an option for a variety of reasons (among them unknown solder connection impedance and variation, contamination, and just no good way to solder to the DUT). Might be a reasonable thing to try here, except it seems like you already have enough range and resolution for your wires (?)


It may help to consider what is being measured. I'm under the impression that we are measuring the properties of wire, not a finished speaker cable. If memory serves the original question related to whether or not various brands of speaker cable had conductivity that was a reasonable match to their specified wire gauge.

Using a 4 terminal measuring procedure usually has the consequence of eliminating the connectors or even the method of connection, from the measurement. That seems very appropriate in this case.
arnyk is offline  
post #255 of 372 Old 03-20-2014, 11:51 AM
AVS Forum Addicted Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 12,343
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3276 Post(s)
Liked: 3363
The problem is making good connection to the wire, which is this case is likely a small probe tip facing a massive (relative to its size) wire bundle. How do you know all the wires are contacted equally/evenly at he probe point? BUT, I agree that in this case it really should not matter and a simple Kelvin probe should work OK. I don't think anyone is disputing that.

Taking a step back, any reasonable measurement should be fine for comparing relative wire sizes, and as far as I can tell Amir's approach is sound, as were yours' and others' before. Perhaps even mine. This offshoot started when Amir needed more time, and I just commented I thought making such measurements was not easy so did not mind the wait. Seems like we're pretty far down the rabbit hole -- I'd rather Amir spent his time measuring than posting. smile.gif

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #256 of 372 Old 03-20-2014, 12:16 PM
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,420
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 851 Post(s)
Liked: 1251
Quote:
Originally Posted by DonH50 View Post

The problem is making good connection to the wire, which is this case is likely a small probe tip facing a massive (relative to its size) wire bundle. How do you know all the wires are contacted equally/evenly at he probe point? BUT, I agree that in this case it really should not matter and a simple Kelvin probe should work OK. I don't think anyone is disputing that.


The 4 terminal measurement scheme helps greatly with that problem. If points A and D are some distance (a foot for example) from B to C then the current is no doubt uniformly permeating the wire in the region that is being measured (B-C)
RUR likes this.
arnyk is offline  
post #257 of 372 Old 03-20-2014, 01:10 PM
AVS Forum Addicted Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 12,343
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3276 Post(s)
Liked: 3363
That is why I said in this case it really should not matter. In my previous work the sense connections at B and C were also called into question, nature of the beast. Led to using very special fixturing and very expensive test equipment.

We are chasing our tails, the only real issue is that Amir needs to quit work and focus on providing us results! smile.gif Not enough hours in a day, a problem I also thoroughly understand....

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #258 of 372 Old 03-20-2014, 02:09 PM
AVS Forum Special Member
 
jamin's Avatar
 
Join Date: May 2001
Location: moot point
Posts: 1,166
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 61 Post(s)
Liked: 76
Amir,
4 -terminal low ohm measures aside, toss in strand count and strand diameter just for giggles. Yes, I know, that can also be fraught with peril !!

plug in to play
Acoustic Mafia - Hear No Evil
jamin is online now  
post #259 of 372 Old 03-20-2014, 04:01 PM
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,829
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1334 Post(s)
Liked: 750
Quote:
Originally Posted by jamin View Post

Amir,
4 -terminal low ohm measures aside, toss in strand count and strand diameter just for giggles. Yes, I know, that can also be fraught with peril !!
Boy, this is as hard to measure as the resistance! smile.gif As long as you accept rough numbers, I just added the total diameter of all the strands. Did you mean the diameter of each one separately? I will look at counting them next...
amirm is offline  
post #260 of 372 Old 03-20-2014, 05:18 PM
AVS Forum Special Member
 
J_Palmer_Cass's Avatar
 
Join Date: May 2005
Posts: 6,604
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 394 Post(s)
Liked: 119
While you are at it, measure the capacitance of the insulation between pairs of wires in the cable. That should be easy for you to do in your spare time!eek.gifbiggrin.gif
J_Palmer_Cass is offline  
post #261 of 372 Old 03-20-2014, 06:00 PM
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,829
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1334 Post(s)
Liked: 750
Quote:
Originally Posted by J_Palmer_Cass View Post

While you are at it, measure the capacitance of the insulation between pairs of wires in the cable. That should be easy for you to do in your spare time!eek.gifbiggrin.gif
I was debating whether to do AC analysis at a later time or not. I will see if I can do that quickly and if I can, I will include it.
amirm is offline  
post #262 of 372 Old 03-21-2014, 11:49 AM
AVS Forum Special Member
 
jamin's Avatar
 
Join Date: May 2001
Location: moot point
Posts: 1,166
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 61 Post(s)
Liked: 76
Quote:
Originally Posted by amirm View Post

Quote:
Originally Posted by jamin View Post

Amir,
4 -terminal low ohm measures aside, toss in strand count and strand diameter just for giggles. Yes, I know, that can also be fraught with peril !!
Boy, this is as hard to measure as the resistance! smile.gif As long as you accept rough numbers, I just added the total diameter of all the strands. Did you mean the diameter of each one separately? I will look at counting them next...
Amir - I was just thinking of measuring a few strands per , um, bundle. Trying to get a number that was reasonable. Not every strand. Course if vendors are playing games with the metal and games with different diameters in a bundle ... fuggedaboutit, cause it won't do any good.

plug in to play
Acoustic Mafia - Hear No Evil
jamin is online now  
post #263 of 372 Old 03-21-2014, 02:15 PM
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,829
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1334 Post(s)
Liked: 750
I have to see if my micrometer is accurate enough for that kind of measurement. If I have time, i will add it but otherwise, will add it later.

FYI I have written the overall report and now shooting some pictures to go with it. So the data should be up later tonight or tomorrow.
DaverJ likes this.
amirm is offline  
post #264 of 372 Old 03-22-2014, 10:12 AM
AVS Forum Special Member
 
jamin's Avatar
 
Join Date: May 2001
Location: moot point
Posts: 1,166
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 61 Post(s)
Liked: 76
No thing really. Just thinking about grabbing a measure to try and "bin" the wire strand size to a gauge #.

plug in to play
Acoustic Mafia - Hear No Evil
jamin is online now  
post #265 of 372 Old 03-22-2014, 10:49 AM
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,829
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1334 Post(s)
Liked: 750
Hello everyone. As promised, here is my analysis of the common 12 Gauge speaker wire. Hope you find it useful smile.gif. I will be creating an online article from this so please critique both technical points and writing.

Introduction
Why test 12 gauge (AWG) wire? 12 AWG speaker wire is a “safe bet” from performance point of view because anything thinner may interact with the low impedance of your speakers and cause the frequency response to vary beyond threshold of hearing (-0.5 dB). That change can “color” the sound.

Once you get to 12 AWG and in reasonable (shorter) lengths, you should be good. This conclusion however only holds if the wire you buy is actually 12 gauge wire and has the nominal resistance that is used in the computation of dB drop. For this reason, it is useful to see if the wires that one can readily buy online or from local sources in US complies with the nominal values for 12 AWG. The measurement in question is “DC resistance” where we measure the resistance of the wire when it is being fed direct current (DC). This is the most basic parameter for cables.

I plan to keep updating this data. So if you like your favorite speaker wire measured, PM me for address and be ready to mail a 4 foot/1.5 meter section of your wire and I will measure and add its value to the measurement table below.

Test Methodology
The purpose of a good speaker cable is to transfer energy with very little drop. That very characteristic makes it very hard to measure the resistance by definition, that is a very small value. Typical (DC) resistance of speaker wire is in the area of 0.0015 ohm/0.15 milliohm per foot. This small resistance puts typical multimeters out of business since they become inaccurate in single digit ohm let alone in thousands of an ohm.

There are different solutions to this problem. The one I opted for is the so called 4-wire or Kelvin measurement invented by Lord Kelvin 100+ years ago. At high level, the 4-wire system separates the leads that provide power to the load (i.e. our speaker wire) from the leads that measure the voltage drop across it (which given the current, tells us the resistance using Ohm’s law). Because the leads are separated, we are now free to provide much more current and as a result, create a larger voltage drop. Not only that, but we also eliminate the effect of meter probe because the current that is going through them is a fraction of what we are feeding the load. Please look online if you like to have more details about its operation.

Unfortunately high-end milliohm meters are quite expensive, some going for as much as $5,000. I don’t do enough of this work to justify investing in them. The unit I have used here is a portable unit which has resolution down to 0.1 milliohm and accuracy of 1% (plus 5d). Its output current is rather low at 200 milliamps since it runs on batteries. That however, is still 200+ times more than standard multimeters which use 1 microamp to 1 milliamp typically for resistance measurements.

In my test fixture, I am using a common, 2-probe system. There are still 4 leads going to the load but they attach to the load in pairs. This removes one of the sources of mistakes (using the wrong probes for high current and voltage measurements) and makes it much faster to test multiple items. Accuracy is still quite high.

As is always the case, the reality and theory are different. A milliohm meter is a very sensitive device. This means that it will actually measure the contact resistance of its own probes. This is easy to back out however by zeroing out its lead resistance first which is what I did. What is not so easy is to guarantee that you put the same contact pressure on the wires in question. There is an easy solution to this which is to use a much longer length of cable and hence, have its resistance swamp the connection load. Problem with that is the wire will coil every which way and won’t match from sample to sample. I wanted a predictable setup where every wire was tested the same way which meant straight and flat.

My solution to the problem was to use a ~3 foot segment of wire that I could hold flat on my desk but then short out one end and measure the resistance as seen from the other end. This does create a new problem in that the twisted end again has certain resistance and variability. To counter that, I put “clamping” load on it in the form of a beefy paper clip. I tested that fix by pushing hard on the connection while the clip was holding it and the difference was negligible. Without that clip, there would be considerable change when I put force on it.

Here is what the final fixture and my test setup looks like:

i-4QWLZhN-L.jpg

Sample Wires Tested:
Here are the samples that I managed to acquire during a two week or so period:

Monoprice 12 AWG Speaker Wire: I bought a 50 foot spool through Amazon third-party service. I paid $25.35 and shipping was “free” (Prime). Monoprice’s own price is lower but you have to pay shipping and I prefer to not create accounts online any more than I have to.

27471.gif

The cable itself has a blue stripe on one of the wires which is useful in identifying which wire is which. The reel was cardboard and the overall impression screamed budget/low-end. The stripped wire did not hold well together due to many soft strands. Stripping it resulted in loosing fair number of strands.

RadioShack 12 AWG “AUVIO” speaker wire: I bought a 50 foot spool this on sale for $39. With tax it came up to $43 or so. Since I picked it up locally there was no shipping.

pRS1-14168346w345.jpg

This is one good looking cable and spool! It oozes quality. The spool is blue and substantial. Likewise the wire looks thick and beautifully wound. I weighed the spool and wire and it was 4.51 pounds. In comparison, the Monoprice was 2.68 pounds. If I put the two next to each other and put the price tag on them, I am pretty sure most people would go for the RadioShack wire. The visual difference is unmistakable.

Parts Express Wired Home SKRL-12-50: I bought a 50 foot spool again through Amazon for $24.20. Shipping was an additional $7.69 for a total of $31.89. I went to their site and it was similar in price with shipping so I bought it from Amazon. It took over 7 days to get this wire. They shipped it quickly but they used economy service to send it to me. Being spoiled by free Prime shipping from Amazon, it was quite annoying to pay nearly $8 and have to wait a week.

100-024_HR_0.jpg

As the listing indicates, this is from a company called Wired Home. It came in a nice blue plastic spool. It was not nearly as substantial as the RadioShack wire but definitely a step above lower end stuff.

Belden 5000UP 12 AWG: This is an in-wall speaker cable. As one of the largest cable suppliers in the world, and set of measured specifications, I thought this would provide a nice baseline to compare others. I could not find 50 foot spool of this wire on Amazon. All that was available through third-parties was 100+. Parts Express sold it however by foot though so I ordered 20 feet. The cost for that was $19.60 and shipping was $14.00 for express delivery.

3666899587_2jHK1Q3F_2105578367_qQS0GBtC_belden5000UP.jpg

The outer wrapping in this cable is thick and substantial. Not to the level of RadioShack wire but still above average. The individual wires inside strip easily and hold their form strongly. It is the closest thing to electrical wire.

Fry’s 12 AWG Wire: It was hard finding this wire at Fry’s Electronic as it was not with the rest of the speaker wires in the AV department. This is what it looks like:

1706615.01.prod.jpg

Price was a reasonable $15.99 for the 50 foot spool. The spool is very light and the wire pretty flexible.

Electrical Wire: This is your typical stranded 12 gauge electrical wire that I had bought from Home Depot. It is a single conductor wire so not very suitable as speaker wire. But I thought I include it as a reference since I had it in my drawer of electrical parts. I don’t have the label handy but it is similar to this:

11ee9e8c-9181-41aa-bf94-896924ed75da_300.jpg

It strips easy because it matches the gradations in the a typical wire stripper but is very stiff.

Colman in-wall 12 AWG: I have a few hundred feet of this in my house. My then contractor (before I started Madrona Digital) selected it without my involvement. I told the contractor to pick “good quality cable” and this is what he bought. The application is non-critical (background music in the kitchen and feeding power to other devices). This is what it kind of looks like:

fvUG-v8A.B

As you can see, it is a typical in-wall (CL3) cable with outer insulation and Belden like inside wires.

ICE 12 AWG Speaker Cable: ICE is one of the “go to” brands of cables for custom AV installers. We use a number of different speaker cables at Madrona and I found this left over reel in the shop and thought I should test it:

Ice-Cable-Speaker-Cable.jpg

BestBuy 12 AWG CableAs with Fry’s, the speaker area had a bunch of wires from Monster and their own house brand but nothing that went up to 12 AWG. I remembered that the automotive section often has heavier gauge wires and that was the case. They had a non-descript 20 foot spool. One conductor is copper colored and the other “silver.” I suspect it is actually aluminum wire.

Canare 4s11
This is a premium in-wall cable. It has four 14 gauge conductors. You can use two of the 14 gauge wires together if you only need one speaker feed which is the way I tested it. Alternatively you can use it as redundancy in case during construction a nail or screw went into it.

CAN4S11.jpg

Coat Hanger: No, you don’t new glasses; I did say coat hanger! biggrin.gif There is an online fish story that says someone performed blind testing of coat hanger against monster cable and nobody could tell the difference. There are other issues with that story but here, I thought I focus on the DC resistance.

11001.jpg

The specimen I used has no brand or label. It is awfully thick though and was very hard to unwind into a straight “wire.” To combat contact resistance, I zeroed my meter by putting the probes next to each other and using that as the new “zero.” In a real situation that contact resistance would also be part of the equation.

Measurements
OK, enough rambling; let’s get into the measurements. The table below shows all that data. The first column is the length of the wire I was testing. I was not anal about keeping the length exactly 3 foot. So instead, I measured the actual segment and used that in the computation. In some cases I had a fixed length already and I used that.

The second column is our key data, the measured resistance in milliohms. Since this would vary based on the length of the wire being tested, I divided its value by the length and arrived at the industry standard milliohms/ft.

Next is the claimed DCR if available. Yes, there are discrepancies between my measurement and theirs. Since these are stranded wires, it is hard to get the exact number the resistance is supposed to be. Likely there are differences between my fixture and the one cable manufacturer used. So the best use of the measurements is as a relative value to compare one wire against another, rather than attempting to match it to any published spec. To that end, I used the measured DC Resistance of Belden cable as the baseline and used that to create a ratio in the next column (“Ratio to Standard”).

The Relative Difference column takes out the value of the Belden cable giving us a “pure” percentage of how much higher or lower the DCR is relative to Belden. In that regard, Belden gets a reference of 0. Negative numbers now mean a wire has higher resistance than Belden and positive numbers the other way around.

The bottom row in green is the Geometric Mean (Geomean) of the column of data above it. Geomean is an average of a set of numbers that doesn’t get thrown off badly by one or more samples being way off the scale. Since that is what I am dealing with here, it makes for a better value than simple average. The number then provides a statistic average of the samples I tested.

Here is the table as computed in my spreadsheet:

i-pCHLdNw.png

And the Relative Difference charted as bar graphs:

i-5hDgfH5.png

I have color coded the underperforming wires in orange. As you can see, Monoprice, Fry’s, Bestbuy and Coat Hanger fall in this bucket. The coat hanger actually went past the bottom of the graph so whatever story there is on how it sounds is quite suspect.

Fry’s and Bestbuy wires must be aluminum cored to have such high resistance. They are not thin enough for the difference to be due to that. I would certainly avoid using both in any high fidelity application.

Of the none-in-wall wires, the RadioShack by far leads the pack on both subjective quality and measured DC Resistance. It managed to slightly outperformed our Belden reference. At $40, that is not much of a premium cost wise considering that you can pick it up in person and be able to instantly use it.

The Monoprice’s resistance is almost twice as high as RadioShack wire but not nearly as bad as the BestBuy and Fry’s no name wires. But being least bad doesn’t translate to good in my book smile.gif. My recommendation is that if you want to go the mail order route, go with the Parts Express Wired Home cable. It outperforms Monoprice both subjectively and in measured resistance (50% lower than Monoprice).

Conclusions
So there it is. Clearly 12 AWG wire is not 12 AWG when you buy a no-name brands. The notion then that you should buy any old wire that says 12 AWG and shopping purely based on price is not a wise one. When you can, buy branded cable that comes with proper specification.
amirm is offline  
post #266 of 372 Old 03-22-2014, 11:23 AM
AVS Forum Special Member
 
Frank Derks's Avatar
 
Join Date: Jul 2002
Location: Region A,B,C
Posts: 2,487
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 539 Post(s)
Liked: 413
http://en.wikipedia.org/wiki/Speaker_wire#Wire_gauge

according to the awg specs the 2 wire 14 awg canare should be about 25% better than your belden 'reference'.

You really should have measured a much longer cable run to circumvent the limitation of your millihohm meter resolution.

A current limited power supply is easy to setup as a current source (a simple psu will do 3..5 Ampere at least).
With a microVolt meter the measured voltage drop across the cable times the current will be more accurate reistance value.

Stereo is simply Multichannel light.
Frank Derks is offline  
post #267 of 372 Old 03-22-2014, 11:52 AM
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,829
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1334 Post(s)
Liked: 750
Quote:
Originally Posted by Frank Derks View Post

http://en.wikipedia.org/wiki/Speaker_wire#Wire_gauge

according to the awg specs the 2 wire 14 awg canare should be about 25% better than your belden 'reference'.
You can't use those tables. Stranded wire resistance varies good bit based on its make up. See this sample set of specifications for 12 gauge: http://www.seas.gwu.edu/~ecelabs/appnotes/PDF/techdat/swc.pdf
Total Strands/Strand Size -- DCR
7/20 - 1.45
19/25 - 1.7
65/30 - 1.75

The high and low vary by 21%. Worse yet, other references show different values. The only reliable reference seems to be for solid conductor. There is just too much variability for one to draw conclusions in the absolute.
Quote:
You really should have measured a much longer cable run to circumvent the limitation of your millihohm meter resolution.
There is nothing wrong with the meter. It has an accuracy of 0.1%+5d which is far lower than 21% above. I explained the issue in the article. Unless you can use the same fixture the manufacturer used, you can't duplicate their numbers. Also keep in mind that temperature creates variations.
Quote:
A current limited power supply is easy to setup as a current source (a simple psu will do 3..5 Ampere at least).
With a microVolt meter the measured voltage drop across the cable times the current will be more accurate reistance value.
Running 5 amps into wire will cause it to heat up and change its resistance. You will have to be awfully quick to perform such measurements as to reduce that effect. But if it is easy and reliable, why not make your measurements for one of the wires and show that it is the same?
amirm is offline  
post #268 of 372 Old 03-22-2014, 12:10 PM
AVS Forum Special Member
 
mcnarus's Avatar
 
Join Date: Nov 2007
Posts: 6,156
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 154 Post(s)
Liked: 381
First of all, Amir, kudos for doing this. Obviously there are some limitations to the approach you took, which others (including you) are more qualified to discuss than I am. So these are a couple of observations which are based on the rebuttable presumption that your measurements are accurate.

The standard resistance of 12 AWG copper wire (listed here, for example) is generally given as 1.59 milliohms, which means that the Belden is overspecced. I'd guess it's somewhere between AWG 10 and 11. All but 3 of the cables you tested are marginally better than 12 AWG. The Monoprice, as someone suggested earlier, is about AWG 13. I would have no hesitance about recommending it for runs up to 50 feet.

Interesting that the two big-box electronics chains are the dogs of the bunch. So when a Best Buy salesman tells you that Monster brand cable is better than the generic, he's probably right!

BTW, I chose the Belden you tested for the best possible reason: my wife liked the neutral color!

If you can't explain how it works, you can't say it doesn't.—The High-End Creed

mcnarus is offline  
post #269 of 372 Old 03-22-2014, 12:52 PM
AVS Forum Special Member
 
cfraser's Avatar
 
Join Date: Aug 2002
Location: Toronto area, Canada
Posts: 1,668
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 285 Post(s)
Liked: 164
Interesting.

I used this for my surrounds/backs/center: http://www.belden.com/techdatas/english/1312A.pdf

It is very nice cable, overkill maybe, but nice materials from OFC copper to the inside polyolefin insulation which is also incredibly easy to strip cleanly. Available in white/gray/black for those who have to look at it too.

Since all my surround speakers have (IMO useless) bi-wiring terminals, I did use all 4 conductors for each speaker. I guess that's like 9 gauge 2c cable...like I said, technical overkill, but it's the labor required more than the materials price so don't want to do it again. smile.gif
cfraser is offline  
post #270 of 372 Old 03-22-2014, 01:14 PM
AVS Forum Special Member
 
Frank Derks's Avatar
 
Join Date: Jul 2002
Location: Region A,B,C
Posts: 2,487
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 539 Post(s)
Liked: 413
Quote:
Originally Posted by amirm View Post

You can't use those tables. Stranded wire resistance varies good bit based on its make up. See this sample set of specifications for 12 gauge: http://www.seas.gwu.edu/~ecelabs/appnotes/PDF/techdat/swc.pdf
Total Strands/Strand Size -- DCR
7/20 - 1.45
19/25 - 1.7
65/30 - 1.75

The high and low vary by 21%. Worse yet, other references show different values. The only reliable reference seems to be for solid conductor. There is just too much variability for one to draw conclusions in the absolute.
There is nothing wrong with the meter. It has an accuracy of 0.1%+5d which is far lower than 21% above. I explained the issue in the article. Unless you can use the same fixture the manufacturer used, you can't duplicate their numbers. Also keep in mind that temperature creates variations.
Running 5 amps into wire will cause it to heat up and change its resistance. You will have to be awfully quick to perform such measurements as to reduce that effect. But if it is easy and reliable, why not make your measurements for one of the wires and show that it is the same?

I doubt heating up will be an issue : running 5A through a 1milliOhm resistor yields 25milli Watts. The changes due to heating up will be insignificant in comparison to the meters resolution issue. in any case it will be virtually the same for every cable under test.

The 1% accuracy stated is for the full scale. You are using the meter near the bottom end of the scale.

At this side of the pond wire is spec'd in mm^2. So comparisons are a bit tricky.

Stereo is simply Multichannel light.
Frank Derks is offline  
Sponsored Links
Advertisement
 
Reply Audio Theory, Setup, and Chat

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off