TCI Cobra interconnects against Chord Chameleon
 

On 2008-07-15, Don Pearce wrote:
John Phillips wrote:
On 2008-07-15, Don Pearce wrote:
Don Pearce wrote:
...
Further to all this, here's the impedance of a standard Monster speaker
cable. R and G effectively vanish from the picture by the time you reach
4kHz. Above that the cable is defined by L and C

http://81.174.169.10/odds/monster.gif

This is clearly a purely inductive cable as far as the amplifier is
concerned, unless of course the load resistance heads north of 100 ohms
at high frequency.

But I don't know what practical relevance this has. Surely a cable's
impedance has little to do with the real world performance of an
amplifier - cable - 'speaker interface except insofar as the impedance
is a measure of the square root of L / C (with R and G thrown in, in
the complex sense).

I have simulated (in GNUCAP & SPICE) such interfaces using equivalents
for:
- a single-section lumped RLCG cable model;
- a multi-section lumped RLCG cable model; and
- a transmission line cable model.

For the same amp and 'speaker, the results for a given cable, however
modelled, did not differ in the audio band, as far as I currently recall,
to any practical engineering significance.

The real-world effects seemed, I think, to be mainly due to the cable's
lumped R and L parameters interacting with the 'speaker's impedance curve.
An ESL-57 'speaker model (with thanks to Jim Lesurf's web site) was
an interesting illustration of some extreme differences in frequency
response that can occur between different cables.


No, cables don't have lumped parameters - they have distributed
parameters - that's what makes them cables. ...

I don't dispute that. But in the real world of audio I think it is
not relevant, as I demonstrated to myself, at least, by checking some
simulations using the different models.

... But the point is this;
wherever the lumped equivalent parameters matter, you will get a better
answer from the distributed model. Speakers are particularly interesting
in that there are many cables available, some of which (from Goertz)
have inductance and capacitane which together come down to around 8 ohms
as a distributed impedance. These cables, despite having enormous
capacitance, are essentially ruler-flat in frequency. There is no
drop-off as might be expected if you consider just the capacitance as a
load to the amplifier. ...

I understand that. But, still, I think you don't need a transmission
line model to show it to an accuracy that is more than sufficient for
engineering purposes.

Do you have particular example where you think the lumped and transmission
line models will differ in a cable-speaker application to a degree that is
practically relevant?

... You can't appreciate how this works unless you
treat it as a cable, and not a couple of lumped components.

I have to disagree. I have simulated Goertz-like cables (with 10-section
lumped models, but only down to 25 ohms nominal). I can easily see how
it works from the results.

And actually, an ESL-57's extreme impedance curve at high audio
frequencies can challenge even low-Z cables with respect to being
ruler-flat in frequency response. Nevertheless it is clear that low-Z
cables are better: I believe because of the low L, and not because of
the high C.

(And the ESL-57 is only problematic at about 18 kHz as I recall it -
so I probably wouldn't hear it at my age.)

--
John Phillips

TCI Cobra interconnects against Chord Chameleon
 

"Don Pearce" wrote in message
et...


As for attenuation per unit length, does it ever matter in a domestic
setting? If there is a little more, just nudge the volume control.

I'd have thought it would for speaker cables, as we are talking about real
power here. A loss of 1dB equates to a waste of 20% of your expensively
produced audio power (and warm up the cable quite nicely to boot!)

David.

TCI Cobra interconnects against Chord Chameleon
 

John Phillips wrote:
On 2008-07-15, Don Pearce wrote:
John Phillips wrote:
On 2008-07-15, Don Pearce wrote:
Don Pearce wrote:
...
Further to all this, here's the impedance of a standard Monster speaker
cable. R and G effectively vanish from the picture by the time you reach
4kHz. Above that the cable is defined by L and C

http://81.174.169.10/odds/monster.gif

This is clearly a purely inductive cable as far as the amplifier is
concerned, unless of course the load resistance heads north of 100 ohms
at high frequency.
But I don't know what practical relevance this has. Surely a cable's
impedance has little to do with the real world performance of an
amplifier - cable - 'speaker interface except insofar as the impedance
is a measure of the square root of L / C (with R and G thrown in, in
the complex sense).

I have simulated (in GNUCAP & SPICE) such interfaces using equivalents
for:
- a single-section lumped RLCG cable model;
- a multi-section lumped RLCG cable model; and
- a transmission line cable model.

For the same amp and 'speaker, the results for a given cable, however
modelled, did not differ in the audio band, as far as I currently recall,
to any practical engineering significance.

The real-world effects seemed, I think, to be mainly due to the cable's
lumped R and L parameters interacting with the 'speaker's impedance curve.
An ESL-57 'speaker model (with thanks to Jim Lesurf's web site) was
an interesting illustration of some extreme differences in frequency
response that can occur between different cables.

No, cables don't have lumped parameters - they have distributed
parameters - that's what makes them cables. ...

I don't dispute that. But in the real world of audio I think it is
not relevant, as I demonstrated to myself, at least, by checking some
simulations using the different models.


Absolutely in real world audio it isn't relevant, but given that either
is equally easy to apply, why not use the one that works at all frequencies?

... But the point is this;
wherever the lumped equivalent parameters matter, you will get a better
answer from the distributed model. Speakers are particularly interesting
in that there are many cables available, some of which (from Goertz)
have inductance and capacitane which together come down to around 8 ohms
as a distributed impedance. These cables, despite having enormous
capacitance, are essentially ruler-flat in frequency. There is no
drop-off as might be expected if you consider just the capacitance as a
load to the amplifier. ...

I understand that. But, still, I think you don't need a transmission
line model to show it to an accuracy that is more than sufficient for
engineering purposes.

Do you have particular example where you think the lumped and transmission
line models will differ in a cable-speaker application to a degree that is
practically relevant?


Not handy. But it is clear that the lumped version of the model is a
lowpass filter, which a cable simply isn't. The area we are dealing with
here is that part of the filter where the flat slope is just starting to
turn down marginally before it gets to the true corner. Now for all
practical purposes, that slope is a good approximation of what happens
in a true cable model when it is mismatched. The problem comes when you
are working in matched conditions - like the Goertz cable, and for the
real cable, like the distributed model there is no turndown. The lumped
approximation fails. You are left with the question of working out the
degree of failure in other conditions.

... You can't appreciate how this works unless you
treat it as a cable, and not a couple of lumped components.

I have to disagree. I have simulated Goertz-like cables (with 10-section
lumped models, but only down to 25 ohms nominal). I can easily see how
it works from the results.

And actually, an ESL-57's extreme impedance curve at high audio
frequencies can challenge even low-Z cables with respect to being
ruler-flat in frequency response. Nevertheless it is clear that low-Z
cables are better: I believe because of the low L, and not because of
the high C.


No, both have equal weight in the equation. If I have two pieces of
cable, one of 10 microhenries and 100 pF per metre, and another of 20
microhenries and 200 pF per metre, they will perform identically.

(And the ESL-57 is only problematic at about 18 kHz as I recall it -
so I probably wouldn't hear it at my age.)


That is the good thing about all of this. The differences, tiny as they
are, are at frequencies at which they simply don't matter anyway.

d

TCI Cobra interconnects against Chord Chameleon
 

David Looser wrote:
"Don Pearce" wrote in message
et...


As for attenuation per unit length, does it ever matter in a domestic
setting? If there is a little more, just nudge the volume control.

I'd have thought it would for speaker cables, as we are talking about real
power here. A loss of 1dB equates to a waste of 20% of your expensively
produced audio power (and warm up the cable quite nicely to boot!)

David.



1dB? You wouldn't even be nudging the control for that - too small to
notice. And power these days is just dirty-cheap; it's why we are all
using those nice low-efficiency speakers.

d

TCI Cobra interconnects against Chord Chameleon
 

On 2008-07-15, Don Pearce wrote:
John Phillips wrote:
Do you have particular example where you think the lumped and transmission
line models will differ in a cable-speaker application to a degree that is
practically relevant?

Not handy. But it is clear that the lumped version of the model is a
lowpass filter, which a cable simply isn't. The area we are dealing with
here is that part of the filter where the flat slope is just starting to
turn down marginally before it gets to the true corner. Now for all
practical purposes, that slope is a good approximation of what happens
in a true cable model when it is mismatched. The problem comes when you
are working in matched conditions - like the Goertz cable, and for the
real cable, like the distributed model there is no turndown. The lumped
approximation fails. You are left with the question of working out the
degree of failure in other conditions.

I am concerned about your use of "matched conditions" WRT the Goertz
cable. Matched conditions don't exist in an amp-cable-speaker system.
Even if you have an "8-ohm" speaker, and an 8-ohm Goertz cable.

1. The amplifier output impedance is not 8 ohms - maybe 10 mOhms for
a good example.

2. I agree that a cable can have an 8-ohm impedance (most are, in
practice much higher, though).

3. The loudspeaker is (almost) never flat 8 ohms. For example, try
this netlist which simulates the ESL-57 in your simulator:

..subckt SPEAKER 1 9
* Quad ESL57 model
L1 1 31 20e-6
R1 31 9 80
L2 31 9 80e-3
L3 31 32 50e-3
R2 32 9 80
C1 31 9 4e-6
R3 31 33 15
R4 33 34 15
C2 34 9 2.5e-6
C3 33 34 5.6e-6
L4 31 35 0.3e-3
R5 35 36 15
C4 36 9 35e-6
..ends

And I can provide netlists for a more conventional loudspeaker (my
"8-ohm" Proac D15s) which show similar wide variations in impedance
with frequency.

... If I have two pieces of
cable, one of 10 microhenries and 100 pF per metre, and another of 20
microhenries and 200 pF per metre, they will perform identically.

I think not in a mismatched system. They certainly perform differently in
the quick frequency response simulation I just did of a 10 mOhm impedance
amplifier driving 5 metres of the two different cables (10-section
lumped model or a single section - same result), each terminated with the
netlist above. When I get home I will check to see if I made an error
(but I can't spare the time just now).

--
John Phillips

TCI Cobra interconnects against Chord Chameleon
 

In article , David Looser
wrote:
"Don Pearce" wrote in message
et...


As for attenuation per unit length, does it ever matter in a domestic
setting? If there is a little more, just nudge the volume control.

I'd have thought it would for speaker cables, as we are talking about
real power here. A loss of 1dB equates to a waste of 20% of your
expensively produced audio power (and warm up the cable quite nicely to
boot!)

OTOH by inserting a series resistance you *reduced* the total power output
by the amplifier. So high resistance cables may save the planet. ...I now
look forwards to some cable merchant flogging cable using this argument.
8-]

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
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TCI Cobra interconnects against Chord Chameleon
 

In article , Don
Pearce
wrote:

As ever with cables, what determines the response is the square root of
the ratio of the inductance to the capacitance. It matter nothing what
each is individually.

The closer you can get that figure to 8, the flatter the speaker
response will be.

Alas, this isn't true unless the speaker is also an 8 Ohm load. I don't
know of any speakers that fit this requirement. Certainly my experience is
that most show wild departures from it. Also, virtually all cables in the
real world seem far from having a uniform impedance across the audio band.

The reality is more like that the source and destination impedances tend to
be lower than the cable impedance, the cable is short in wavelength terms,
etc. The result is that - for domestic LS cables - the cable series R and L
can alter the response, but the shunt C has almost no effect unless them
amplifier has some RF problem.

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
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TCI Cobra interconnects against Chord Chameleon
 

In article , John Phillips
wrote:
On 2008-07-14, Don Pearce wrote:
John Phillips wrote:
... (At least as far as GNUCAP calculates - the real world is often
different.)

As ever with cables, what determines the response is the square root
of the ratio of the inductance to the capacitance. It matter nothing
what each is individually.

Err... My amp-cable-speaker frequency response simulations rather
suggest the load (loudspeaker) impedance curve has influence on the
frequency response - not just the cable's L and C. Or have I
misunderstood you?

The interaction between the cable R and L and the load will probably have
the main effects on level and response. Although this assumes the amp has a
reasonably low o/p impedance which perhaps may not be correct for some
(mainly valve) designs.)

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
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TCI Cobra interconnects against Chord Chameleon
 

In article Mr6dnYcrJMOI_OHVnZ2dneKdnZydnZ2d@plusnet, Don Pearce
wrote:
Jim Lesurf wrote:
In article , Don

1) That the cable impedance (and EM wave velocity) is set by the L'
and C' prime values. Thus ignoring R' and G'. If you actually examine
the situations for LS cables at *audio* frequencies the actual values
for Zc and V are generally very different to those you get simply by
using L' and C'. Sometimes orders of magnitude different. And strongly
frequency dependent.

You are right about the effect consider R' and G', but they are
unimportant for the following reason - they only become factors that
affect the cable impedance at low frequencies, at which they make no
difference.

The snag being that "low frequencies" here generally covers the bulk of the
audio band when one looks at the kinds of cables people use.

See, for example

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

Think of the above as a 'sneak preview' of some of the results that HFN
should be publishing soon. :-) It shows the impedance and EM wave
velocity values for a random selection of cables. ( did actually model
rather more cables than this, but decided to just use some. Otherwise the
graph had so many lines they became impossible to disentangle by eye!)

The lines with the red squares show an example of the "8 Ohm" woven cables.
You can see the actual impedance is well above 8 Ohms over much of the
frequency range.

The above was from some historic published data. A later article will
publish some new measurements I have done which give similar sorts of
values and results.

G' probably doesn't matter much for most cases. But L' may well, whilst
with unmatched use most cables can be well modelled using R' and L' and
ignoring C' as well as G'. This is the result I get from comparing models
with measured results. It stems from the general rule that the source and
load impedance is usually well below the cable characteristic impedance,
and the cable is short in wavelength terms. This is for audio frequencies,
of course. I got some other results from modelling and measuring at
ultrasonic/RF frequencies. But the first article focusses on the audio
range, and leaves high frequencies to a later article. :-)


Once you are up into the region where cable parameters can
cause unflatness, they are second order effects, and the hf model which
only considers L and C is just fine.

2) You assume matched operation. But with domestic LS use this is
generally far from being so. When you examine more practical
situations the behaviour is very different to a matched case - which
would be almost impossible to arrange at audio due to the strong
frequency dependence of the impedance of the cables.


No, I'm not assuming matched operation, although there are cables which
come close for loudspeakers.

It seems to be a rare situation as in general both the cable impedance and
the LS impedance are frequency dependent, using with quite distinct
patterns of variation. And when the operation isn't matched then it tends
to turn out as I have described, based both on models and measurements.


What I'm saying is that a model which only looks at L or C in isolation
will always give wrong answers.

Rather depends on what you mean by "wrong". No model will give "right"
answers in all cases if you require absolute precision. But the reality
seems to be that in the audio band for LS cables in domestic situations you
get accurate results if you use R' and L' and ignore C' in general.


People talk about cables being capacitive on the basis of a high
pF/metre figure. This is nonsense; for a cable to be capacitive it must
have a characteristic impedance lower than the load impedance -
something which almost never happens with speaker cables, which in 99%
of cases will be inductive.

Indeed. Hence the points I have been making.

Been doing a lot of both modelling and measurements on this recently.
All being well, the detailed results will be appearing in HFN soon in
a series of articles. But the basic situation is that with LS cables
the primary effects are due to L' and R'. C' may have some effect on
amp stability.


Is this true at 20kHz? I can't remember my analysis results in detail,
but I seem to think it wasn't so.

Have a look at the gif whose URL I gave above for some examples. The "8
Ohm" cable comes close around 20kHz, but most other cables that most people
will be using come no-where near.

I was quite surprised by some of the other results I got from
measurements. Food for thought. So I have been re-thinking some of my
ideas about LS cables. But my base position is still that - when using
a decent amplifier - that low R' and L' are sensible, and that C'
doesn't matter much. And that working in terms of using L' and C' as
a 'pair' probably doesn't tell you much about the audio behaviour.


Not so sure I'm with you there.

Perhaps when you see the fuller results in the articles you will be
pursuaded. :-)

Not sure if the first article will be in the issue of HFN due in a week or
so. But with luck it will be published them. There are two other articles
that follow on from that at present, and in the pipeline. I found doing
them threw up some results I hadn't always expected, but I am not sure it
ended up changing my mind.

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
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Audio Misc http://www.audiomisc.co.uk/index.html

TCI Cobra interconnects against Chord Chameleon
 

In article , Don
Pearce


Further to all this, here's the impedance of a standard Monster speaker
cable. R and G effectively vanish from the picture by the time you reach
4kHz. Above that the cable is defined by L and C

http://81.174.169.10/odds/monster.gif

I'll have a look. I can't recall if I included that cable in the graphic I
just put up as the selection was random - i.e. I deliberately didn't choose
examples I 'liked', so dunno at present which ones I ended up using! One
exception was that I chose to include the "8 Ohm" cable as being of special
interest in this context.

Main point was the sheer range of values, and the diversity of variations
in Z and V with audio frequency. Your chance of finding a cable-load
matched arrangement for domestic LS systems seems quite slim.

This is clearly a purely inductive cable as far as the amplifier is
concerned, unless of course the load resistance heads north of 100 ohms
at high frequency.

Yes. That is consistent with my main point. That in general the LS cables
people use end up with relatively high characteristic impedances, and so L'
tends to be more important than C'. Often essentially dominates the effects
produced. There are exceptions, but I'd say they were quite rare.

The opposite occurs with interconnects. There the load is generally high
impedance compared with the cable, and so C' becomes more significant
than L'.

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
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