TCI Cobra interconnects against Chord Chameleon
 

"Arny Krueger" wrote in message
...

No harm was done by the wire, so nothing needs to be done to fix it.
In that case why were you arguing in a previous thread that balanced lines
were superior to unbalanced ones in normal home ( 2m) interconnects.

Keith

TCI Cobra interconnects against Chord Chameleon
 

In article , Don
Pearce
wrote:

OK - wave velocity is simply a factor of geometry - specifically how
much of the electric field is within the dielectric and how much in air.
Generally the closer the two conductors are to each other, the more the
field is concentrated within the insulator - and of course the lower
the impedance. But the one is not because of the other. It is quite
easy to make a ten ohm cable with no insulator - velocity equal to free
space light.

Perhaps you could make a 5 metre length of your "10 Ohm cable with no
insulator - velocity equal to free space light" and send it to me. I can
then test it and compare its properties as a LS cable with the other types
I have measured and analysed. :-)

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

TCI Cobra interconnects against Chord Chameleon
 

Jim Lesurf wrote:
In article , Don
Pearce
wrote:


An explanation, it is simple. we are trying to model something
inappropriately. In a limited range of cases it can - pretty much by
chance - give results fairy close to the correct ones. But a cable isn't
a lowpass filter, and never will be. The distributed model is the only
one which will always provide the right answer.

Motes versus beams, I fear. :-)

Distributed models also only provide the "right answer" if you ensure all
the cable parameters have the correct frequency dependence *and* you model
an appropriate situation.


As it is so trivial to use, I use it rather than trying to work out how
appropriate a lumped equivalent is going to be, how many sections I need
to chop it up into etc etc etc.

in my experience, when doing this you also need to worry about the
computational accuracy and how your model is being computationally
implimented. Otherwise a 'more accurate' model in principle ends up giving
results less like reality. :-)


That is always the way with models - even when you model by using the
real thing.

The above is a particular problem when using a package like Spice, MathCad,
etc, where you may not know how the package is using the values you have
specified to work out an answer.

As to models being complicated, I think two parameters, Zchar and length

Erm... Three, as you'd also need the propagation constant.[1] And of course
both Zc and will have two values each since they are complex (unless you
are deciding to ignore some parameters...)


A cable's Zchar isn't complex. And yes you are right, you do need a
propagation constant.

are quite a lot easier to use than perhaps thirty inductors and sixty
one capacitors.

..but not much different in terms of "being complicated" to using three RLC
values for the cable. :-)


Ah but that never works. You have to use them over and over again to
achieve an arbitrary degree of accuracy.

BTW I'm also puzzled by why you need 2n+1 caps for n inductors for your
model. Why not n+1 and just use half values at the ends? Or are you just
getting the number up to make the point you want to make? :-)


I was thinking of cascading pi sections, but of course what you do in
practice is combine adjacent caps into one.

Slainte,

Jim

[1] Unless, of course, you are insisting upon the rather unrealistic
approach of assuming people always compare/choose LS cables on the basis of
moving the amp towards and away from the speakers to be able to compare
cables of appropriately different lengths in order to force them all to
have the same nominal propagation delay when matched (which in general,
they aren't, of course.) That said, I'd agree that moving the amp to just
beside the speaker and using cables of mininal length makes sense...

If you can do it. :-)


what I actually assume is that people choose speaker cable wisely on the
basis of being it fairly meaty, safe in the knowledge that it is going
to be good enough. My speaker cables are only about six feet long so
they can be pretty much anything.

d

TCI Cobra interconnects against Chord Chameleon
 

"keithr" wrote in message

"Arny Krueger" wrote in message
...

No harm was done by the wire, so nothing needs to be
done to fix it.

In that case why were you arguing in a previous thread
that balanced lines were superior to unbalanced ones in
normal home ( 2m) interconnects.

That discussion was about interface circuitry, not cable. One of the goals
of using balanced I/O is to remove the characteristics of the interconnect
as far as is reasonably possible.

BTW I recently had a situation where the line receiver circuitry in a piece
of equipment failed, and the interface became unbalanced. Signal passed
regardless because one side was still passing signal well. But there was no
cancellation of noise. Dynamic range was basically so poor as to be
unusable. When replaced with a correctly-operating line receiver, all was
well. The cable length that caused excess noise when unbalanced was 3 feet.
The cable length that was quiet when balanced operation was restored ranged
from 3 feet to 150 feet.

TCI Cobra interconnects against Chord Chameleon
 

Out of interest I decided to do a comparison of the simple lumped CRLG
model and the analytical transmission line model for 5 metres of various LS
cables into an 8 Ohm load. The results are shown at

http://jcgl.orpheusweb.co.uk/temp/DiffGain.gif

Top graphs shows the gains (losses) for a set of different cable
measurements. These results use the transmission line method. i.e. use
reflection and transmission coefficients for the amp-cable and cable-load
junctions derived from the cable, source, and load impedances. Then use the
propagation constant to include the cable loss and propagation delay.

The bottom graphs show what you get if these results are subtracted from
the results that simply use the C'R'L'G' values multiplied by the cable
length to get the four lumped CRLG values. Note the vertical scale on these
plots!

For simplicity I assumes the amp o/p impedance was zero.

In general, the difference between the two approaches seems to be well
below 0.01dB over the audio band. In practice it seems doubtful we'd either
have measured values accurate enough to worry about 0.01 dB, or that the
cable values remain stable to that level of precision. I also doubt anyone
would be able to hear such a difference and say, "hey! your result is out
by 0.0001 dB!" ;-

The results were done quickly, but confirm similar checks I've done in the
past, and support my view that there is generally no real need to use the
full transmission line method for computation in such practical cases. The
cable is far too short at audio frequencies to have to employ the
transmission line approach. Simply a matter of which approach you prefer to
get much the same results. However, for other reasons I explain elsewhere,
the lumped CLRG approach is an easier predictor for people to use at audio
frequency. :-)

FWIW I also tend to avoid using series of lumped elements in a line, as
that tends in my experience to simply give rise to computation limitations
causing misleading results. If you wish to use the transmission line
approach it seems better to me to use the simple analytic solution.

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

TCI Cobra interconnects against Chord Chameleon
 

In article , Don
Pearce
wrote:
Jim Lesurf wrote:



As to models being complicated, I think two parameters, Zchar and
length

Erm... Three, as you'd also need the propagation constant.[1] And of
course both Zc and will have two values each since they are complex
(unless you are deciding to ignore some parameters...)


A cable's Zchar isn't complex.


Ermm... actually, in general, it is. Have a look at the general expressions
in something like Ramo and Whinnery for a transmission line that has
losses. As soon as you include R' and G' then Zchar become complex *unless*
you can arrange to satisfy the Heavyside criterion.

Having a 'real' Zchar is a simplification undergrad texts use a lot of the
time - obtained by ignoring the effects of R' and G'.


And yes you are right, you do need a propagation constant.

are quite a lot easier to use than perhaps thirty inductors and sixty
one capacitors.

..but not much different in terms of "being complicated" to using
three RLC values for the cable. :-)


Ah but that never works. You have to use them over and over again to
achieve an arbitrary degree of accuracy.

Not so. Have a look at the results I just posted. The accuracy can easily
be far better than the accuracy with which you measured or controlled the
cable values in the first place. :-)

BTW I'm also puzzled by why you need 2n+1 caps for n inductors for
your model. Why not n+1 and just use half values at the ends? Or are
you just getting the number up to make the point you want to make? :-)


I was thinking of cascading pi sections, but of course what you do in
practice is combine adjacent caps into one.

OK. Should say I once spent a lot of time doing that - particularly for
lines with nonlinear properties. But when doing so I found that some of the
tools people use for computation can easily give misleading results.
Beware. :-)

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

TCI Cobra interconnects against Chord Chameleon
 

Jim Lesurf wrote:
In article , Don
Pearce
wrote:

OK - wave velocity is simply a factor of geometry - specifically how
much of the electric field is within the dielectric and how much in air.
Generally the closer the two conductors are to each other, the more the
field is concentrated within the insulator - and of course the lower
the impedance. But the one is not because of the other. It is quite
easy to make a ten ohm cable with no insulator - velocity equal to free
space light.

Perhaps you could make a 5 metre length of your "10 Ohm cable with no
insulator - velocity equal to free space light" and send it to me. I can
then test it and compare its properties as a LS cable with the other types
I have measured and analysed. :-)

Slainte,

Jim


Ooh - no way to make that and get it to you, but not too much trouble to
make it yourself. Get a couple of metal strips 5 metres by 35mm. Place
them one above the other as near air-spaced as possible about 1mm apart.
A matchstick every foot or so should do it. Not too fussed about the
width as I imagine it doesn't matter about it being exactly 10 ohms.

Not too flexible, I'm afraid ;-)

d

TCI Cobra interconnects against Chord Chameleon
 

Jim Lesurf wrote:
Out of interest I decided to do a comparison of the simple lumped CRLG
model and the analytical transmission line model for 5 metres of various LS
cables into an 8 Ohm load. The results are shown at

http://jcgl.orpheusweb.co.uk/temp/DiffGain.gif

Top graphs shows the gains (losses) for a set of different cable
measurements. These results use the transmission line method. i.e. use
reflection and transmission coefficients for the amp-cable and cable-load
junctions derived from the cable, source, and load impedances. Then use the
propagation constant to include the cable loss and propagation delay.

The bottom graphs show what you get if these results are subtracted from
the results that simply use the C'R'L'G' values multiplied by the cable
length to get the four lumped CRLG values. Note the vertical scale on these
plots!

For simplicity I assumes the amp o/p impedance was zero.

In general, the difference between the two approaches seems to be well
below 0.01dB over the audio band. In practice it seems doubtful we'd either
have measured values accurate enough to worry about 0.01 dB, or that the
cable values remain stable to that level of precision. I also doubt anyone
would be able to hear such a difference and say, "hey! your result is out
by 0.0001 dB!" ;-

The results were done quickly, but confirm similar checks I've done in the
past, and support my view that there is generally no real need to use the
full transmission line method for computation in such practical cases. The
cable is far too short at audio frequencies to have to employ the
transmission line approach. Simply a matter of which approach you prefer to
get much the same results. However, for other reasons I explain elsewhere,
the lumped CLRG approach is an easier predictor for people to use at audio
frequency. :-)

FWIW I also tend to avoid using series of lumped elements in a line, as
that tends in my experience to simply give rise to computation limitations
causing misleading results. If you wish to use the transmission line
approach it seems better to me to use the simple analytic solution.

Slainte,

Jim


Interesting - particularly that the biggest error shows with the cable
that has the flattest response. That is kind of what I expect.

d

TCI Cobra interconnects against Chord Chameleon
 

In article , Don
Pearce
wrote:
Jim Lesurf wrote:
In article , Don
Pearce wrote:


Perhaps you could make a 5 metre length of your "10 Ohm cable with no
insulator - velocity equal to free space light" and send it to me. I
can then test it and compare its properties as a LS cable with the
other types I have measured and analysed. :-)


Ooh - no way to make that and get it to you, but not too much trouble to
make it yourself. Get a couple of metal strips 5 metres by 35mm. Place
them one above the other as near air-spaced as possible about 1mm apart.
A matchstick every foot or so should do it.

Your response rather confirms what I thought. The above construction
is rather impractical. It is also unlikely to provide an impedance
that is fairly close to 10 Ohms across the entire audio band...

How thick do you assume the metal strips will need to be to keep the
impedance perfectly uniform at 10 Ohms? Also, are you confident that a
single matchstick per (non-SI) 'foot' will be enough to get accurate
geometry? I must confess that your constructional skills are greater than
mine if you can make the above work. Particularly in terms of avoiding
fringing field effects by keeping the whole things clear of anything else,
keeping it absolutely plane, etc, etc.

Not too fussed about the width as I imagine it doesn't matter about it
being exactly 10 ohms.

Odd. I thought you were saying it *would* be 10 Ohms... :-)

Not too flexible, I'm afraid ;-)

Nor, it seems, likely to be very precisely in accord with your initial
description of its performance. :-)

I appreciate that such constructions look nice and simple in undergrad
textbooks. Often because the analysis ignores various aspects to provide a
simple analysis that is easy to examine at the end of a course. :-)

But when you come to analyse them in more practical detail, or try to
build them, it tends to be the case that they don't quite perform as you
might expect. :-)

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

TCI Cobra interconnects against Chord Chameleon
 

Jim Lesurf wrote:
In article , Don
Pearce
wrote:
Jim Lesurf wrote:
In article , Don
Pearce wrote:

Perhaps you could make a 5 metre length of your "10 Ohm cable with no
insulator - velocity equal to free space light" and send it to me. I
can then test it and compare its properties as a LS cable with the
other types I have measured and analysed. :-)


Ooh - no way to make that and get it to you, but not too much trouble to
make it yourself. Get a couple of metal strips 5 metres by 35mm. Place
them one above the other as near air-spaced as possible about 1mm apart.
A matchstick every foot or so should do it.

Your response rather confirms what I thought. The above construction
is rather impractical. It is also unlikely to provide an impedance
that is fairly close to 10 Ohms across the entire audio band...


But the impedance really only starts to matter towards the top end of
the band. At lower frequencies the whole thing is just too short
(electrically) to make a difference. That is why you don't see
unflatness at the bottom end even though the impedance is heading skywards.

How thick do you assume the metal strips will need to be to keep the
impedance perfectly uniform at 10 Ohms? Also, are you confident that a
single matchstick per (non-SI) 'foot' will be enough to get accurate
geometry? I must confess that your constructional skills are greater than
mine if you can make the above work. Particularly in terms of avoiding
fringing field effects by keeping the whole things clear of anything else,
keeping it absolutely plane, etc, etc.


I was working on 1mm for the calculations.

Not too fussed about the width as I imagine it doesn't matter about it
being exactly 10 ohms.

Odd. I thought you were saying it *would* be 10 Ohms... :-)


This is all about velocity, remember? My point was that we were in
danger of a "post hoc propter hoc" connection between impedance and
propagation velocity. This was really a gedankenexperiment to show that
they aren't really associated other than by the mechanics of construction.

Not too flexible, I'm afraid ;-)

Nor, it seems, likely to be very precisely in accord with your initial
description of its performance. :-)

I appreciate that such constructions look nice and simple in undergrad
textbooks. Often because the analysis ignores various aspects to provide a
simple analysis that is easy to examine at the end of a course. :-)

But when you come to analyse them in more practical detail, or try to
build them, it tends to be the case that they don't quite perform as you
might expect. :-)


I designed one of the first TEM cells for Multitone, a paging company
for testing the sensitivity of pagers. It was eight feet long and
comprised a stripline about a foot above the groundplane, with tapered
feeds down to N-type connectors. It performed exactly to theory.

d