TCI Cobra interconnects against Chord Chameleon
 

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?

--
John Phillips

TCI Cobra interconnects against Chord Chameleon
 

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?


Yes - what I am saying is that to work out the effect of the cable on
the response, you don't consider L or C in isolation - they only have
meaning as a pair, using the calculation above.

d

TCI Cobra interconnects against Chord Chameleon
 

John Phillips wrote:

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.

That would be to be anticipated.

Graham

TCI Cobra interconnects against Chord Chameleon
 

In article , Don
Pearce
wrote:
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?


Yes - what I am saying is that to work out the effect of the cable on
the response, you don't consider L or C in isolation - they only have
meaning as a pair, using the calculation above.

Afraid I have to politely disagree with you. Although you aren't very clear
about what you mean by "as a pair" :-)

You are making two implict assumptions which do not normally hold for
domestic LS cabling.

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.

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.

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.

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.

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:
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?


Yes - what I am saying is that to work out the effect of the cable on
the response, you don't consider L or C in isolation - they only have
meaning as a pair, using the calculation above.

Afraid I have to politely disagree with you. Although you aren't very clear
about what you mean by "as a pair" :-)

You are making two implict assumptions which do not normally hold for
domestic LS cabling.

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

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.

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.

d

TCI Cobra interconnects against Chord Chameleon
 

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


Yes - what I am saying is that to work out the effect of the cable on
the response, you don't consider L or C in isolation - they only have
meaning as a pair, using the calculation above.

Afraid I have to politely disagree with you. Although you aren't very
clear
about what you mean by "as a pair" :-)

You are making two implict assumptions which do not normally hold for
domestic LS cabling.

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

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.

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.

d

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.

d

TCI Cobra interconnects against Chord Chameleon
 

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.

--
John Phillips

TCI Cobra interconnects against Chord Chameleon
 

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

d

TCI Cobra interconnects against Chord Chameleon
 

Don Pearce wrote:

No, cables don't have lumped parameters - they have distributed
parameters - that's what makes them cables. 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. You can't appreciate how this works unless you
treat it as a cable, and not a couple of lumped components.


Are you saying that Goertz speaker cables act as transmission lines
with a characteristic impedance of 8 ohms? If so, you should also state
the low corner frequency below which the characteristic impedance rises,
and the attenuation per unit length.

--
Eiron.

TCI Cobra interconnects against Chord Chameleon
 

Eiron wrote:
Don Pearce wrote:

No, cables don't have lumped parameters - they have distributed
parameters - that's what makes them cables. 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. You can't appreciate how this
works unless you treat it as a cable, and not a couple of lumped
components.


Are you saying that Goertz speaker cables act as transmission lines
with a characteristic impedance of 8 ohms? If so, you should also state
the low corner frequency below which the characteristic impedance rises,
and the attenuation per unit length.


The point about that corner is that it is a phenomenon of the low end,
where it makes essentially no difference. Were it something that
happened as you went up in frequency it would matter much more. 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. Anyway, to
achieve the low characteristic impedance you need a fair amount of
copper, so I'm guessing they aren't too bad.

d