Audio Cable Tester Requirement

W

Wayne Kerr Man

Guest
Someone proposed an idea to customize a LCR meter for audio cable tester. It is a very doable project. I would welcome your contribution to give me your opinion on requirement. I will soon report here what we will have collected.
 
J

jneutron

Senior Audioholic
Wayne Kerr Man said:
Someone proposed an idea to customize a LCR meter for audio cable tester. It is a very doable project. I would welcome your contribution to give me your opinion on requirement. I will soon report here what we will have collected.
Hello there, Wayne Kerr Man...(what a name...didn't your parents like you)

I realize that I am but a simplistic audiophyte :( , so what possible questions could I have that you are not already aware of???

Speaker wire test..

Minimum energy storage of a transmission line occurs when the characteristic impedance of the load matches that of the line..I would like to see valid measurement of cable inductance from about 250 pH per foot to over 300nH per foot..with a ten foot cable...and software derivation of the cable impedance.

Thinner dielectric runs, such as 1 to 2 mil teflon, kapton, tefzel, kynar and enamel, for a speaker run, can broach up to 10% of the dielectric withstanding voltage. Operation in that regime can force non linear dielectric properties..is it possible to measure the capacitance with a large DC voltage on the cable? I am interested in also the measurement of capacitance vs either voltage slew rate, or voltage potential...during the high voltage excitation.

Skin effect: Accurate R measurement up to 1 Mhz, to include lateralization issues up to 1.5 uSec. R measurement at various current slew rates, as skin effect is actually a response to a current slew, not a frequency or voltage issue.

The ability to measure inductive dither as a result of high spl environments...but, I think this one may be better left for another day..


Ahhhh. where to start...

Welcome, Wayne Kerr Man..
Cheers, John
 
W

Wayne Kerr Man

Guest
measurement of Cp vs Cs

A quick answer to the measurement of Cp vs Cs is that for large capacitors, the impedence effect is presented in serial circuits; on the other hand, for small capacitor, it is in parallel circuits. For details, please wait for an article on measurement techniques of cable wires.
 
W

Wayne Kerr Man

Guest
high voltage effect

For your interest in supplying high DC voltage, how high and what kind of range do you need? Typically in LCR meter, we can test up to 2 volts with 10mv stages. For transformer, users ask for 10V. Can you specify your needs?
 
W

Wayne Kerr Man

Guest
John's

In the skin effect testing, how high the current do you need? Is 1Amp sufficient? Also, can you explain laterization issues for audio cables?
 
J

jneutron

Senior Audioholic
Wayne Kerr Man said:
In the skin effect testing, how high the current do you need? Is 1Amp sufficient? Also, can you explain laterization issues for audio cables?
Hmmm...a little explaining...

Skin effect is taught as a simple frequency dependent effect, and is presented entirely as the calculation of the depth a TEM wave penetrates the conductor. This simplistic textbook explanation does not consider the current within the conductor, nor the internal inductance, the 15 nH per foot per conductor number.

In actuality, skinning of the current within a conductor is the reaction of the conductor to the rate of change of the magnetic field created by the current. At DC, this magnetic field increases from the center of the wire as a 1/r relation..

So, for audio, one is not simply interested in the frequency of the signal, but, the rate of change of the current..yes, proportional to the frequency, but more importantly, dependent on the impedance of the loop. Measurement of the skin effect as it pertains to wires has to be at low impedance, a standard of either 4 or 8 ohms would suffice. One amp is probably adequate to look for changes.

A question would be...is this a necessary feature for a new piece of equipment, or perhaps, a software module for a flexible platform...if demonstrated to be a significant effect worthy of inclusion.

Lateralization....

Humans distinguish direction of a source by amplitude and phase...or, more appropriately, left-right timing delays. Here is a graph, simple calculation of L-R timing delays presented to a pair of ears, located 6 inches apart, ten feet from the plane of the source..(don't know where the graph will end up...hopefully right here...didn't..oh well)


Looking at this graph, one notes that close to center stage, the timing cues we use to locate an object run in the low tens of microseconds. In fact, if one were to dither the signal in the 1 to 5 uSec range (as a full range speaker would do as a result of low frequency excursion), one finds that humans are more sensitive to localization cues L-R...down to about 1.5 uSec. This, from the Nordmark paper.

These results infer very wide bandwidth capabilities in humans, which is of course, not the case...it does, however point to the possibility that for rigid and correct soundstage within a stereo system, one has to consider the reproduction system's ability to provide temporally correct audio up into the hundreds of kilohertz. At this time, I've seen nothing to denote what we are sensitive to with respect to the lateralization cues...Nordmark hypothesized zero crossings, but I'm not confident in that. That premise would imply that all localization content will be lost if low frequency sound waves of sufficient amplitude are present, as zero crossings would not happen for much of the hf content as a result of the summation of signals within the ear canal...I'd think it more so rate of change of pressure...

Needless to say, if 1.5 uSec cues are actually involved, skin effect could become relevant..

I think I'll hold off on the cap voltage thing for now...what is being discussed is certainly enough for a while, don't you think?

Cheers, John
 

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gene

gene

Audioholics Master Chief
Administrator
the reproduction system's ability to provide temporally correct audio up into the hundreds of kilohertz.
Whao Jon, I mean John ;) What audio system do you know that can do this? No digital media can do this (nor should it!) let alone any loudspeaker. Cabinet diffraction effects and room acoustics severly limit a speakers frequency response much beyond 20kHz, especially off axis which is where we listen. In addition, extending an audio system bandwidth out this far will compromise signal to noise ratio and possibly system stability. Certainly in this regard, the cable is far from being the limiting factor or cause of concern.
 
J

jneutron

Senior Audioholic
gene said:
Whao Jon, I mean John ;) What audio system do you know that can do this? No digital media can do this (nor should it!) let alone any loudspeaker. Cabinet diffraction effects and room acoustics severly limit a speakers frequency response much beyond 20kHz, especially off axis which is where we listen. In addition, extending an audio system bandwidth out this far will compromise signal to noise ratio and possibly system stability. Certainly in this regard, the cable is far from being the limiting factor or cause of concern.
Now now...be nice.... ;) I'm doing my best to explain this as simply as possible, y'all donna want me to pull da stops, now does ya??? :eek:

Do not confuse the ability to reproduce a 500 Khz sine wave with the ability to accurately reproduce two independent signals with 2 uSec temporal accuracy.

I am not talking about system bandwidths up there..my reference to hundreds of khz capability is not full power sine wave, but simply the inverse of the timing numbers I am talking about.

What I am saying is that humans can distinguish left to right delays at the ten or so microsecond level...think of it this way...put a source behind an optically opaque screen...now, with your eyes open, have the sound made behind the screen, and point to it..if you can "see" and point to the source to within 5 inches at 10 feet, you have shown the ability to distinguish left to right delays to less than 20 microseconds..if you can get within two inches, you show 8 microsecond ability..one foot is 40 micro...

Soundstaging is the virtual image produced in our brain, much of it due to the system's ability to correctly reproduce those timing relations. Mess up the timing from one channel to the other, and the cues we use for imaging are messed with..It's not a case of putting one's head in a vise, but what each ear hears in time, regardless of head position..we internally correct for small head rotations..

I am not concerned here with the speaker temporal or amplitude response..nor, the matching of each speaker...but rather, how the brain generates an image, and how that image is altered by timing relations..

BTW...Jon wouldn't be having this discussion. :confused: ..as this discussion here, at this site, is all about testing...electrical ones, clearly defined..with criteria......need I say more? :) (of course, that was just a cheap shot even if it may be historically accurate.....in actuality, he is welcome to participate here, as are all. As I have stated elsewhere, two hands are needed to clap)

I have a lot of graphs and equations to support and define what I speak of, but your "darn" site doesn't allow me to post the pics in the body of the text, and I don't think I can get multiple pics on the same post...

Here, however, is a graph showing energy storage in a 10 foot long wire...8 ohm load, 100 Wrms, vs the characteristic impedance of the wire, dielectric coefficient is 2.7..note that the energy, while in microjoules, is actually a significant fraction of the instantaneous energy delivered to an 8 ohm load at 10 Khz...the further away from match between line and load, the more lead (or lag) will be evident.. Is it enough to meet the 1.5 to say, 20 usec temporal shift needed to trash the soundstage image? Don't know yet..the distributed L/C transmission line model , I haven't modelled.

Cheers, John
 

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W

Wayne Kerr Man

Guest
requirement

Now, from the requirement of measurement point of view, can I conclude that 1. we need to build in 1AMP DC bias and 2. we need to support upto say 500KHz. 3. Graphics capability is needed to show impedence changes wrt frequency changes. 4. Some equations needed to built-in for showing effects and impacts. Make sense? What are effects and impacts important for Audio system designer? for users? and system sales persons?
 
J

jneutron

Senior Audioholic
Wayne Kerr Man said:
Now, from the requirement of measurement point of view, can I conclude that 1. we need to build in 1AMP DC bias and 2. we need to support upto say 500KHz. 3. Graphics capability is needed to show impedence changes wrt frequency changes. 4. Some equations needed to built-in for showing effects and impacts. Make sense? What are effects and impacts important for Audio system designer? for users? and system sales persons?
1. DC bias....I do not know to what end the dc bias current would do anything. If the assumption of superposition linearity is used, then a DC bias current to introduce additional internal wire storage will not be of any use.

If one wishes to test superposition by watching the internal inductance collapse from a steady state to zero, then the 1 amp dc is useful...

Measuring skin based inductive drop will be impedance dependent, via current slew..so I would say the need to test inductance using a drive capable of sufficient resolution into a 4 ohm load.

2. 500 Khz seems reasonable enough..a meg would be a little better, as 500Khz vs 1.5 uSec is rather close...for my load, I'll be working it out as far as I can, 60 Mhz being the limit of the synthesizer I have in my office.

I'm finding that the frequency dependent L is of sufficient size to warrant measurement, as it will affect timing at the 1.5 uSec level. Measurement of L to that degree will be a good step towards correlating (or of course, lack of correlation) the virtual image constructed within our brain with the geometry of the cable..

Ideally, of course, the capacitance should be dealt with in a similar fashion...albeit, measurement of capacitance vs the dc voltage within the cable...so a large signal dc voltage capability of say, 40 volts dc, with a frequency scan of capacitance. Some of the more exotic cables will run in the 200 to 1000 pf per foot range...consistent with the equation LC=1031*Dielectric coefficient.

At some point, a discussion of amplifier damping factor vs quadrant of operation will have to take place...Does Wayne Kerr have any interest in the measurement of damping factor in that fashion?

Cheers, John
 
W

Wayne Kerr Man

Guest
audio tester

Yes, DC bias is intended for checking when certain measurements run out of range. Regarding the frequency range, we can have different model from 500K upto 10Meg.
About Amplifier damping, yes, we can try it. Any special technique needed?
 
J

jneutron

Senior Audioholic
Wayne Kerr Man said:
Yes, DC bias is intended for checking when certain measurements run out of range. Regarding the frequency range, we can have different model from 500K upto 10Meg.
About Amplifier damping, yes, we can try it. Any special technique needed?
For skin, the ac test current has to drive into 4 or 8 ohm load impedance. Otherwise, current slew will be consistent with line impedance maximum..

10 Mhz will be overkill for audio....1 Mhz is a factor of 2 to 5 over lateralization numbers, so I'd say stick to that max...test setup errors will be bad enough at 500Khz, and hugely more so with low impedance..

Do you have anyone there who is an expert in amplifier output configurations and damping measurements?

I recommend testing the ability of an amplifier to maintain damping and phase shift at high frequencies, while pushing a low frequency into a reactive load..this forces the output stage heavily into a reactive load line, forcing the amplifier to swallow power in quadrants 2 and 4...forcing huge die heating transients and causing the thermal tracking circuits to lag..

First order of business will be a power load capable of pure resistive current draw at half a Mhz..

If you do not have anyone who is current in these measurement techniques, you will have to wait...if so, have him or her contact me for more details...

If this proceeds, I recommend another thread specifically for damping factor discussion.

Cheers, John
 
U

Unregistered

Guest
jneutron said:
Now now...be nice.... ;)
Do not confuse the ability to reproduce a 500 Khz sine wave with the ability to accurately reproduce two independent signals with 2 uSec temporal accuracy.

I am not talking about system bandwidths up there..my reference to hundreds of khz capability is not full power sine wave, but simply the inverse of the timing numbers I am talking about.
RBCD format, though bandlimited to 22khz, apparently has extremely high timing accuracy, in the general range you cite as being a target. This is a product of bandwidth and dynamic range, not just the bandwidth of the system. See this powerpoint presentation from David Griesinger(acoustics physisct, Lexicon)(I could not find the preprint for details of the tests summarized in the pp presentation).:

http://world.std.com/~griesngr/intermod.ppt

Additionally, you will find it is possible to manipulate a 44.1/16 audio file at this level of resolution(shift/move waveforms) in an audio editor application such as CoolEdit, etc.

-Chris
 
WmAx

WmAx

Audioholic Samurai
UNREGISTERED reply was from me. I forgot to sign in before submitting.

The PP presentation is from a 2002 Munich AES conference according to the header it is listed under on Griesinger's page, but their is a date confllict in the PP presentation.

BTW, you can contact Griesinger at this address for further details:

dg@lexicon.com

SOrry if my reply seems a little out of context -- I'm only concerend with the bandwidth vs. timing accuracy issue discussed here.

-Chris
 
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J

jneutron

Senior Audioholic
WmAx said:
UNREGISTERED reply was from me. I forgot to sign in before submitting.

The PP presentation is from a 2002 Munich AES conference according to the header it is listed under on Griesinger's page, but their is a date confllict in the PP presentation.

BTW, you can contact Griesinger at this address for further details:

dg@lexicon.com

SOrry if my reply seems a little out of context -- I'm only concerend with the bandwidth vs. timing accuracy issue discussed here.

-Chris

Nah, it's certainly within context...

I had that discussion a while ago with Dan Banquer, over in aa props..A coupla guys there, Ted Smith among them, explained to me in some technical detail, how the format was capable of the timing we were talking about..vs my recommendation to Dan that he use vinyl as a source.

It does seem weird, I'll admit, to consider 1.5 uSec timing issues with a 22Khz limited bandwidth..

As far as I can see, the timing issues I speak of are impedance dependent...as in, it is much more difficult to even measure high current slews at low impedance...that's why I'm making a very accurate load resistor setup..

Welcome to the party, Chris..

Cheers, John

PS....OH MY GOODNESS!!! will wonders never cease!!!!!

I am now an "enthusiast"...HOLY COW...stop the presses.... :eek:
 
W

wankerr

Audiophyte
How can someone measure an amplifier's damping factor?
 
D

Dan Banquer

Full Audioholic
Damping Factor

Damping factor is just a fancy name for output impedance.
d.b.
 
U

Unregistered

Guest
wankerr said:
How can someone measure an amplifier's damping factor?
(I apologize in advance for the simplistic prelude.)

Damping factor is the ability of the amplifier to control the voltage of the load.

For a pure resistance, that is never an issue..that has a pure, V=I*R relationship..

For a pure inductance or capacitance, there is the old ELI the ICE man...for inductive, E leads I....capacitance, I leads E..

Most speakers are not pure R, which means the amplifier not only has to provide the voltage and current to drive the speaker, but it has to contend with the energy that is stored in the speaker...that energy will try to make the amplifier output deviate from ideal...it is how the amplifier deals with that deviation that is measured as damping factor..

As Dan said, it is output impedance...meaning, the equivalent resistor connected in series with the ideal voltage source the amplifier represents..

A simple measure...put 1 ampere DC into the output terminal of the amp, while it is on...then measure the voltage across the amp output..one volt there means the output impedance is one ohm...one millivolt means one milliohm impedance..Damping factor is the ratio between the speaker load, and the amp impedance...for 1 milliohm, the damping factor with an 8 ohm load would be 8000.

Now...that was a DC test, not a normal audio signal...in reality, the amplifier has to control the load through the audio band...20 to 20K...

My question is this: if the amp is driving 100 wrms at 35 hz into the speaker, the speaker may be inductive, causing the instantaneous output voltage to not be in phase with the current. At that time, the energy being dissipated in the output transistors is larger...amp wants one polarity, speaker is at the other..voltage across the pass elements is more that would be normally..way off the load line..

How well can an amplifier control the load, when it is pushing a reactive load really hard? How does the high frequency damping factor change when the low frequencies are pushing? Given that there are transient thermal time constants pertaining to silicon die mount and powering, how does one measure amp response under heavy dissipation?

And, the real question? Under high power reactive loading, how well does the amplifier control signal timing relationships, at the 1.5 uSec level? Does a bass line cause temporal shifting of lateralization clues?(big note here...that is something the audio guys call "blurring") Can it? Would that even be measured using FFT technology? (short answer there is no, but this is not yet an FFT limitation discussion..)

Sorry for the long ex...graphs and pictures woulda been easier, but my scanner is at home..

Cheers, John
 
J

jneutron

Senior Audioholic
bummer

That last post one was me...I forgot to log in...

John
 
gene

gene

Audioholics Master Chief
Administrator
John;

Does a bass line cause temporal shifting of lateralization clues?
What frequencies are you talking about? Low frequency bass (where the most amplifier power is required) below 80Hz is omnidirectional and the ear cannot perceive directionality or lateral clues? I suggest reading some of the white papers authored by Dr. Floyd Toole and Thomas Holman (formerly of THX). These guys are dead on about bass and I don't really follow you here.

Also, beyond a certain minimal measurable damping factor, it becomes more of an exercise in academics rather than a real world concern.

Check out the article lord helmet Pierce authored on this topic.
Damping Factor in Amplifiers
 
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