(Stewart Pinkerton) wrote in message


It may be that you object to using transmission line theory, because
it is quite unnessary to do so.

It's also utterly pointless, because you can never get anywhere near a
matched system.

Using a transmission line model does not necessitate having a matched
system. One can uses a voltage source and any impedance for a
termination.


Likewise, either model method will give virtually the same answers.
Nowadays, it is quicker and easier (less typing) to enter a
transmission line model, than to type in a componet (L,C) model. Use
whatever way floats your boat.

That's likely true, but again, why bother to do *any* kind of speaker
cable modelling?




This thread started with someone asking about the inductance of
various cable geometrys. Many people have the belief that speaker
cable inductance is always seen by the amplifier. If they saw a
component model of an 8 Ohm speaker cable, they might find out this is
not always true. For example, look at the following 8 Ohm speaker
cable model:

------0.267 uH--------0.267 uH-------0.267 uH------------
| | | | |
Gen 0.0042uf 0.0042uF 0.0042uF 8 Ohms
| | | | |
----------------------------------------------------------

The cable wire's inductance is 0.800 uH, but the generator sees a pure
resistance. No inductive reactance,(no inductance) and no roll off, at
high frequencies.

So, a simple cable model could dispell a common misconception.



No conventional speaker cable has a characteristic impedance even
close to 300 ohms, even the most extreme high-inductance commercial
cable (my Naim NACA5, as it happens) only has an impedance of around
120 ohms. One *could* of course use 300 ohm antenna feeder as speaker
cable, but it wouldn't work very well........................

You are right, the characteristic impedance is 120 Ohms.

Bob Stanton

(Stewart Pinkerton) wrote in message


It may be that you object to using transmission line theory, because
it is quite unnessary to do so.

It's also utterly pointless, because you can never get anywhere near a
matched system.

Using a transmission line model does not necessitate having a matched
system. One can uses a voltage source and any impedance for a
termination.


Likewise, either model method will give virtually the same answers.
Nowadays, it is quicker and easier (less typing) to enter a
transmission line model, than to type in a componet (L,C) model. Use
whatever way floats your boat.

That's likely true, but again, why bother to do *any* kind of speaker
cable modelling?




This thread started with someone asking about the inductance of
various cable geometrys. Many people have the belief that speaker
cable inductance is always seen by the amplifier. If they saw a
component model of an 8 Ohm speaker cable, they might find out this is
not always true. For example, look at the following 8 Ohm speaker
cable model:

------0.267 uH--------0.267 uH-------0.267 uH------------
| | | | |
Gen 0.0042uf 0.0042uF 0.0042uF 8 Ohms
| | | | |
----------------------------------------------------------

The cable wire's inductance is 0.800 uH, but the generator sees a pure
resistance. No inductive reactance,(no inductance) and no roll off, at
high frequencies.

So, a simple cable model could dispell a common misconception.



No conventional speaker cable has a characteristic impedance even
close to 300 ohms, even the most extreme high-inductance commercial
cable (my Naim NACA5, as it happens) only has an impedance of around
120 ohms. One *could* of course use 300 ohm antenna feeder as speaker
cable, but it wouldn't work very well........................

You are right, the characteristic impedance is 120 Ohms.

Bob Stanton

On Sat, 10 Jan 2004 17:32:48 GMT,
wrote:

Stewart Pinkerton wrote:

That's likely true, but again, why bother to do *any* kind of speaker
cable modelling?

OK, since I started this whole horrible thread, I figure I can toss out
an answer to this one.

Pure knowledge. Modelling cables can prove what we know--that beyond
a very easily obtainable point, cables are irrelevant. Furthermore,
we can find out where that point is, and for lack of a better phrase,
how irrelevant the differnt factors are.

For instance, 12 gauge vs. 14 gauge wire isn't particularly important
in speaker cables, but it's a lot closer to being a valid factor than
say, capacitance or even worse, characteristic impedance.

So modelling helps those of us who DON'T know this stuff to learn it.
It also provides worthwhile information for those who are running long
(maybe in-wall?) speaker cables; and for that matter, also for those
who are designing their own amps.

Fair enough, can't argue with anyone wishing to improve their
knowledge. I was simply trying to point out that we don't need to
apply quantum mechanics to the design of patio furniture.

Of course, that doesn't address which model to use, and the answer is
pretty obvious in any field: Use the model which most simply and closely
matches your conditions. For audio of any sort, that does NOT mean a
transmission line model!

Anyways, my two bits worth on why I asked about cables in the very
first place.

So, it's all your fault then? :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 10 Jan 2004 17:32:48 GMT,
wrote:

Stewart Pinkerton wrote:

That's likely true, but again, why bother to do *any* kind of speaker
cable modelling?

OK, since I started this whole horrible thread, I figure I can toss out
an answer to this one.

Pure knowledge. Modelling cables can prove what we know--that beyond
a very easily obtainable point, cables are irrelevant. Furthermore,
we can find out where that point is, and for lack of a better phrase,
how irrelevant the differnt factors are.

For instance, 12 gauge vs. 14 gauge wire isn't particularly important
in speaker cables, but it's a lot closer to being a valid factor than
say, capacitance or even worse, characteristic impedance.

So modelling helps those of us who DON'T know this stuff to learn it.
It also provides worthwhile information for those who are running long
(maybe in-wall?) speaker cables; and for that matter, also for those
who are designing their own amps.

Fair enough, can't argue with anyone wishing to improve their
knowledge. I was simply trying to point out that we don't need to
apply quantum mechanics to the design of patio furniture.

Of course, that doesn't address which model to use, and the answer is
pretty obvious in any field: Use the model which most simply and closely
matches your conditions. For audio of any sort, that does NOT mean a
transmission line model!

Anyways, my two bits worth on why I asked about cables in the very
first place.

So, it's all your fault then? :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 10 Jan 2004 17:32:48 GMT,
wrote:

Stewart Pinkerton wrote:

That's likely true, but again, why bother to do *any* kind of speaker
cable modelling?

OK, since I started this whole horrible thread, I figure I can toss out
an answer to this one.

Pure knowledge. Modelling cables can prove what we know--that beyond
a very easily obtainable point, cables are irrelevant. Furthermore,
we can find out where that point is, and for lack of a better phrase,
how irrelevant the differnt factors are.

For instance, 12 gauge vs. 14 gauge wire isn't particularly important
in speaker cables, but it's a lot closer to being a valid factor than
say, capacitance or even worse, characteristic impedance.

So modelling helps those of us who DON'T know this stuff to learn it.
It also provides worthwhile information for those who are running long
(maybe in-wall?) speaker cables; and for that matter, also for those
who are designing their own amps.

Fair enough, can't argue with anyone wishing to improve their
knowledge. I was simply trying to point out that we don't need to
apply quantum mechanics to the design of patio furniture.

Of course, that doesn't address which model to use, and the answer is
pretty obvious in any field: Use the model which most simply and closely
matches your conditions. For audio of any sort, that does NOT mean a
transmission line model!

Anyways, my two bits worth on why I asked about cables in the very
first place.

So, it's all your fault then? :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 10 Jan 2004 17:32:48 GMT,
wrote:

Stewart Pinkerton wrote:

That's likely true, but again, why bother to do *any* kind of speaker
cable modelling?

OK, since I started this whole horrible thread, I figure I can toss out
an answer to this one.

Pure knowledge. Modelling cables can prove what we know--that beyond
a very easily obtainable point, cables are irrelevant. Furthermore,
we can find out where that point is, and for lack of a better phrase,
how irrelevant the differnt factors are.

For instance, 12 gauge vs. 14 gauge wire isn't particularly important
in speaker cables, but it's a lot closer to being a valid factor than
say, capacitance or even worse, characteristic impedance.

So modelling helps those of us who DON'T know this stuff to learn it.
It also provides worthwhile information for those who are running long
(maybe in-wall?) speaker cables; and for that matter, also for those
who are designing their own amps.

Fair enough, can't argue with anyone wishing to improve their
knowledge. I was simply trying to point out that we don't need to
apply quantum mechanics to the design of patio furniture.

Of course, that doesn't address which model to use, and the answer is
pretty obvious in any field: Use the model which most simply and closely
matches your conditions. For audio of any sort, that does NOT mean a
transmission line model!

Anyways, my two bits worth on why I asked about cables in the very
first place.

So, it's all your fault then? :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

(Bob-Stanton) wrote in message



Schemetic didn't print out right on previous message.




not always true. For example, look at the following 8 Ohm speaker
cable model:

----0.267 uH-----0.267 uH-------0.267 uH------------
| | | | |
Gen 0.0042uf 0.0042uF 0.0042uF 8 Ohms
| | | | |
----------------------------------------------------

The cable wire's inductance is 0.800 uH, but the generator sees a pure
resistance. No inductive reactance,(no inductance) and no roll off, at
high frequencies.

(Bob-Stanton) wrote in message



Schemetic didn't print out right on previous message.




not always true. For example, look at the following 8 Ohm speaker
cable model:

----0.267 uH-----0.267 uH-------0.267 uH------------
| | | | |
Gen 0.0042uf 0.0042uF 0.0042uF 8 Ohms
| | | | |
----------------------------------------------------

The cable wire's inductance is 0.800 uH, but the generator sees a pure
resistance. No inductive reactance,(no inductance) and no roll off, at
high frequencies.

(Bob-Stanton) wrote in message



Schemetic didn't print out right on previous message.




not always true. For example, look at the following 8 Ohm speaker
cable model:

----0.267 uH-----0.267 uH-------0.267 uH------------
| | | | |
Gen 0.0042uf 0.0042uF 0.0042uF 8 Ohms
| | | | |
----------------------------------------------------

The cable wire's inductance is 0.800 uH, but the generator sees a pure
resistance. No inductive reactance,(no inductance) and no roll off, at
high frequencies.

(Bob-Stanton) wrote in message



Schemetic didn't print out right on previous message.




not always true. For example, look at the following 8 Ohm speaker
cable model:

----0.267 uH-----0.267 uH-------0.267 uH------------
| | | | |
Gen 0.0042uf 0.0042uF 0.0042uF 8 Ohms
| | | | |
----------------------------------------------------

The cable wire's inductance is 0.800 uH, but the generator sees a pure
resistance. No inductive reactance,(no inductance) and no roll off, at
high frequencies.

Stewart Pinkerton wrote:

Fair enough, can't argue with anyone wishing to improve their
knowledge. I was simply trying to point out that we don't need to
apply quantum mechanics to the design of patio furniture.

No arguments there. I certainly never suggested that a transmission
line model was relevant.

So, it's all your fault then? :-)

Absolutely! Although I must confess, I usually have to work harder than
this to stir up ****. :-)

Colin

Stewart Pinkerton wrote:

Fair enough, can't argue with anyone wishing to improve their
knowledge. I was simply trying to point out that we don't need to
apply quantum mechanics to the design of patio furniture.

No arguments there. I certainly never suggested that a transmission
line model was relevant.

So, it's all your fault then? :-)

Absolutely! Although I must confess, I usually have to work harder than
this to stir up ****. :-)

Colin

Stewart Pinkerton wrote:

Fair enough, can't argue with anyone wishing to improve their
knowledge. I was simply trying to point out that we don't need to
apply quantum mechanics to the design of patio furniture.

No arguments there. I certainly never suggested that a transmission
line model was relevant.

So, it's all your fault then? :-)

Absolutely! Although I must confess, I usually have to work harder than
this to stir up ****. :-)

Colin

Stewart Pinkerton wrote:

Fair enough, can't argue with anyone wishing to improve their
knowledge. I was simply trying to point out that we don't need to
apply quantum mechanics to the design of patio furniture.

No arguments there. I certainly never suggested that a transmission
line model was relevant.

So, it's all your fault then? :-)

Absolutely! Although I must confess, I usually have to work harder than
this to stir up ****. :-)

Colin

Schemetic didn't print out right on previous message.
It looks OK on "Perview message".

One last try:



----0.267 uH-----0.267 uH-------0.267 uH------------
| | | |
0.0042uf 0.0042uF 0.0042uF 8
| | | |
----------------------------------------------------

Schemetic didn't print out right on previous message.
It looks OK on "Perview message".

One last try:



----0.267 uH-----0.267 uH-------0.267 uH------------
| | | |
0.0042uf 0.0042uF 0.0042uF 8
| | | |
----------------------------------------------------

Schemetic didn't print out right on previous message.
It looks OK on "Perview message".

One last try:



----0.267 uH-----0.267 uH-------0.267 uH------------
| | | |
0.0042uf 0.0042uF 0.0042uF 8
| | | |
----------------------------------------------------

Schemetic didn't print out right on previous message.
It looks OK on "Perview message".

One last try:



----0.267 uH-----0.267 uH-------0.267 uH------------
| | | |
0.0042uf 0.0042uF 0.0042uF 8
| | | |
----------------------------------------------------

(Svante) wrote in message


OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.


I can send you a circuit analysis program that will do transmission
lines, if you want. It's an old DOS program, but it's works well.



the simplest basic
requirement of a transmission line model, that the signal takes a
certain amount of time to pass through.

Probably you would know this by experience. Just as you know the hand
is enough to kill the mosquito. Of course, in case there is a doubt,
grab the magnum and see if the mosquito dies.

I know a signal takes a certain length of time to pass through the
transmission line, not because of my experience with circuits, but
because of the velocity of light.


I don't mind that sound arrives 100 ns late to my ears. This tells me
that RF models of cables ARE overkill (but applicable) and the great
margin tell me that simpler models probably would do OK. And even if a
really poor model would yield a delay of 1 ms, I would not mind.



How do you test to see if your computer model behaves like a real
cable? The quickest way and easiest way is the see if it has correct
delay. If a cable model doesn't predict the delay correctly, the
chances are it will not predict the impedance, or the frequeny
response correctly either.


In my opinion, characteristic impedance and delay are unimportant in
the audio case.

Characteristic impedance, and cable length (delay), are all that are
needed for the prediction of rolloff at any frequencies, audio or RF.
The one caveat being that the R and G (conductances of the cable )
must be much lower than XL and XC of the cable.

What I wonder is if the transmission line model
predicts frequency response changes in the audio band (like a simple
RLC model does), given a frequency-varying load.

The transmission line model is accurate at audio frequenies. All
(real) loads vary with frequency. Circuit analysis programs are
designed to handle this.

If you take a
typical, or better, a slightly ill-behaved load to get "worst case",
how much effect will the cable have on the frequency response, within
the audio band.

About 0.01 dB at 20KHz. Much less at lower frequenices.


I bet you end up with less than 0.1 dB.

You win the bet.

IMO the
frequency-varying load in combination with the series resistance and
possibly inductance accounts for most of this level variation.



Correct. Maybe 90 % of the level varitation is due to series
resistance.


Anyway, how does the transmission line model you use work, actually?
Isn't it actually a large number of RLC elements connected in series
("one for each cm of the cable")?

The model uses no RLC elements.

The circuit analysis program looks that the cables's forward and
reverse transmission (gain and phase). It also looks at the
characteristic impedance, and the specified loss of the cable. From
this, it fiqures out the four scattering parameters of the cable
(easy). It converts these scattering pararmeters into Y parameters,
and then enters the Y-parameters into the circuit matrix as
conductances.

It is actually simpler for the computer to figure out the Y-parameters
of a transmission line, than it is to for it figure out the
Y-parameters of a resistor! You see, the resistor has series (lead)
inductance and parallel (body) capacitance. The computer must reduce
the complex resistor circuit down to two nodes before it enters the
resistor's conductance into the circuit matrix. It takes about as long
for computer to calculate a resistor's conductance, as it takes to
calculate a transmission line's conductance.

Many people think that a transmission line model is overly complicated
(overkill). The computer thinks of the transmission line as simpler
than a single resistor. Ironic isn't it?

Bob Stanton

(Svante) wrote in message


OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.


I can send you a circuit analysis program that will do transmission
lines, if you want. It's an old DOS program, but it's works well.



the simplest basic
requirement of a transmission line model, that the signal takes a
certain amount of time to pass through.

Probably you would know this by experience. Just as you know the hand
is enough to kill the mosquito. Of course, in case there is a doubt,
grab the magnum and see if the mosquito dies.

I know a signal takes a certain length of time to pass through the
transmission line, not because of my experience with circuits, but
because of the velocity of light.


I don't mind that sound arrives 100 ns late to my ears. This tells me
that RF models of cables ARE overkill (but applicable) and the great
margin tell me that simpler models probably would do OK. And even if a
really poor model would yield a delay of 1 ms, I would not mind.



How do you test to see if your computer model behaves like a real
cable? The quickest way and easiest way is the see if it has correct
delay. If a cable model doesn't predict the delay correctly, the
chances are it will not predict the impedance, or the frequeny
response correctly either.


In my opinion, characteristic impedance and delay are unimportant in
the audio case.

Characteristic impedance, and cable length (delay), are all that are
needed for the prediction of rolloff at any frequencies, audio or RF.
The one caveat being that the R and G (conductances of the cable )
must be much lower than XL and XC of the cable.

What I wonder is if the transmission line model
predicts frequency response changes in the audio band (like a simple
RLC model does), given a frequency-varying load.

The transmission line model is accurate at audio frequenies. All
(real) loads vary with frequency. Circuit analysis programs are
designed to handle this.

If you take a
typical, or better, a slightly ill-behaved load to get "worst case",
how much effect will the cable have on the frequency response, within
the audio band.

About 0.01 dB at 20KHz. Much less at lower frequenices.


I bet you end up with less than 0.1 dB.

You win the bet.

IMO the
frequency-varying load in combination with the series resistance and
possibly inductance accounts for most of this level variation.



Correct. Maybe 90 % of the level varitation is due to series
resistance.


Anyway, how does the transmission line model you use work, actually?
Isn't it actually a large number of RLC elements connected in series
("one for each cm of the cable")?

The model uses no RLC elements.

The circuit analysis program looks that the cables's forward and
reverse transmission (gain and phase). It also looks at the
characteristic impedance, and the specified loss of the cable. From
this, it fiqures out the four scattering parameters of the cable
(easy). It converts these scattering pararmeters into Y parameters,
and then enters the Y-parameters into the circuit matrix as
conductances.

It is actually simpler for the computer to figure out the Y-parameters
of a transmission line, than it is to for it figure out the
Y-parameters of a resistor! You see, the resistor has series (lead)
inductance and parallel (body) capacitance. The computer must reduce
the complex resistor circuit down to two nodes before it enters the
resistor's conductance into the circuit matrix. It takes about as long
for computer to calculate a resistor's conductance, as it takes to
calculate a transmission line's conductance.

Many people think that a transmission line model is overly complicated
(overkill). The computer thinks of the transmission line as simpler
than a single resistor. Ironic isn't it?

Bob Stanton

(Svante) wrote in message


OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.


I can send you a circuit analysis program that will do transmission
lines, if you want. It's an old DOS program, but it's works well.



the simplest basic
requirement of a transmission line model, that the signal takes a
certain amount of time to pass through.

Probably you would know this by experience. Just as you know the hand
is enough to kill the mosquito. Of course, in case there is a doubt,
grab the magnum and see if the mosquito dies.

I know a signal takes a certain length of time to pass through the
transmission line, not because of my experience with circuits, but
because of the velocity of light.


I don't mind that sound arrives 100 ns late to my ears. This tells me
that RF models of cables ARE overkill (but applicable) and the great
margin tell me that simpler models probably would do OK. And even if a
really poor model would yield a delay of 1 ms, I would not mind.



How do you test to see if your computer model behaves like a real
cable? The quickest way and easiest way is the see if it has correct
delay. If a cable model doesn't predict the delay correctly, the
chances are it will not predict the impedance, or the frequeny
response correctly either.


In my opinion, characteristic impedance and delay are unimportant in
the audio case.

Characteristic impedance, and cable length (delay), are all that are
needed for the prediction of rolloff at any frequencies, audio or RF.
The one caveat being that the R and G (conductances of the cable )
must be much lower than XL and XC of the cable.

What I wonder is if the transmission line model
predicts frequency response changes in the audio band (like a simple
RLC model does), given a frequency-varying load.

The transmission line model is accurate at audio frequenies. All
(real) loads vary with frequency. Circuit analysis programs are
designed to handle this.

If you take a
typical, or better, a slightly ill-behaved load to get "worst case",
how much effect will the cable have on the frequency response, within
the audio band.

About 0.01 dB at 20KHz. Much less at lower frequenices.


I bet you end up with less than 0.1 dB.

You win the bet.

IMO the
frequency-varying load in combination with the series resistance and
possibly inductance accounts for most of this level variation.



Correct. Maybe 90 % of the level varitation is due to series
resistance.


Anyway, how does the transmission line model you use work, actually?
Isn't it actually a large number of RLC elements connected in series
("one for each cm of the cable")?

The model uses no RLC elements.

The circuit analysis program looks that the cables's forward and
reverse transmission (gain and phase). It also looks at the
characteristic impedance, and the specified loss of the cable. From
this, it fiqures out the four scattering parameters of the cable
(easy). It converts these scattering pararmeters into Y parameters,
and then enters the Y-parameters into the circuit matrix as
conductances.

It is actually simpler for the computer to figure out the Y-parameters
of a transmission line, than it is to for it figure out the
Y-parameters of a resistor! You see, the resistor has series (lead)
inductance and parallel (body) capacitance. The computer must reduce
the complex resistor circuit down to two nodes before it enters the
resistor's conductance into the circuit matrix. It takes about as long
for computer to calculate a resistor's conductance, as it takes to
calculate a transmission line's conductance.

Many people think that a transmission line model is overly complicated
(overkill). The computer thinks of the transmission line as simpler
than a single resistor. Ironic isn't it?

Bob Stanton

(Svante) wrote in message


OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.


I can send you a circuit analysis program that will do transmission
lines, if you want. It's an old DOS program, but it's works well.



the simplest basic
requirement of a transmission line model, that the signal takes a
certain amount of time to pass through.

Probably you would know this by experience. Just as you know the hand
is enough to kill the mosquito. Of course, in case there is a doubt,
grab the magnum and see if the mosquito dies.

I know a signal takes a certain length of time to pass through the
transmission line, not because of my experience with circuits, but
because of the velocity of light.


I don't mind that sound arrives 100 ns late to my ears. This tells me
that RF models of cables ARE overkill (but applicable) and the great
margin tell me that simpler models probably would do OK. And even if a
really poor model would yield a delay of 1 ms, I would not mind.



How do you test to see if your computer model behaves like a real
cable? The quickest way and easiest way is the see if it has correct
delay. If a cable model doesn't predict the delay correctly, the
chances are it will not predict the impedance, or the frequeny
response correctly either.


In my opinion, characteristic impedance and delay are unimportant in
the audio case.

Characteristic impedance, and cable length (delay), are all that are
needed for the prediction of rolloff at any frequencies, audio or RF.
The one caveat being that the R and G (conductances of the cable )
must be much lower than XL and XC of the cable.

What I wonder is if the transmission line model
predicts frequency response changes in the audio band (like a simple
RLC model does), given a frequency-varying load.

The transmission line model is accurate at audio frequenies. All
(real) loads vary with frequency. Circuit analysis programs are
designed to handle this.

If you take a
typical, or better, a slightly ill-behaved load to get "worst case",
how much effect will the cable have on the frequency response, within
the audio band.

About 0.01 dB at 20KHz. Much less at lower frequenices.


I bet you end up with less than 0.1 dB.

You win the bet.

IMO the
frequency-varying load in combination with the series resistance and
possibly inductance accounts for most of this level variation.



Correct. Maybe 90 % of the level varitation is due to series
resistance.


Anyway, how does the transmission line model you use work, actually?
Isn't it actually a large number of RLC elements connected in series
("one for each cm of the cable")?

The model uses no RLC elements.

The circuit analysis program looks that the cables's forward and
reverse transmission (gain and phase). It also looks at the
characteristic impedance, and the specified loss of the cable. From
this, it fiqures out the four scattering parameters of the cable
(easy). It converts these scattering pararmeters into Y parameters,
and then enters the Y-parameters into the circuit matrix as
conductances.

It is actually simpler for the computer to figure out the Y-parameters
of a transmission line, than it is to for it figure out the
Y-parameters of a resistor! You see, the resistor has series (lead)
inductance and parallel (body) capacitance. The computer must reduce
the complex resistor circuit down to two nodes before it enters the
resistor's conductance into the circuit matrix. It takes about as long
for computer to calculate a resistor's conductance, as it takes to
calculate a transmission line's conductance.

Many people think that a transmission line model is overly complicated
(overkill). The computer thinks of the transmission line as simpler
than a single resistor. Ironic isn't it?

Bob Stanton

wrote in message


So modelling helps those of us who DON'T know this stuff to learn it.
It also provides worthwhile information for those who are running long
(maybe in-wall?) speaker cables; and for that matter, also for those
who are designing their own amps.

Of course, that doesn't address which model to use, and the answer is
pretty obvious in any field: Use the model which most simply and closely
matches your conditions. For audio of any sort, that does NOT mean a
transmission line model!


Show me your model please.

Bob Stanton

wrote in message


So modelling helps those of us who DON'T know this stuff to learn it.
It also provides worthwhile information for those who are running long
(maybe in-wall?) speaker cables; and for that matter, also for those
who are designing their own amps.

Of course, that doesn't address which model to use, and the answer is
pretty obvious in any field: Use the model which most simply and closely
matches your conditions. For audio of any sort, that does NOT mean a
transmission line model!


Show me your model please.

Bob Stanton

wrote in message


So modelling helps those of us who DON'T know this stuff to learn it.
It also provides worthwhile information for those who are running long
(maybe in-wall?) speaker cables; and for that matter, also for those
who are designing their own amps.

Of course, that doesn't address which model to use, and the answer is
pretty obvious in any field: Use the model which most simply and closely
matches your conditions. For audio of any sort, that does NOT mean a
transmission line model!


Show me your model please.

Bob Stanton

wrote in message


So modelling helps those of us who DON'T know this stuff to learn it.
It also provides worthwhile information for those who are running long
(maybe in-wall?) speaker cables; and for that matter, also for those
who are designing their own amps.

Of course, that doesn't address which model to use, and the answer is
pretty obvious in any field: Use the model which most simply and closely
matches your conditions. For audio of any sort, that does NOT mean a
transmission line model!


Show me your model please.

Bob Stanton

Bob-Stanton wrote:

wrote in message

Show me your model please.

Feel free to **** off, Bob!

You're the one who has the chip on his shoulder, and the one who
seems determined to prove himself. I have nothing to prove to you.

Colin

Bob-Stanton wrote:

wrote in message

Show me your model please.

Feel free to **** off, Bob!

You're the one who has the chip on his shoulder, and the one who
seems determined to prove himself. I have nothing to prove to you.

Colin

Bob-Stanton wrote:

wrote in message

Show me your model please.

Feel free to **** off, Bob!

You're the one who has the chip on his shoulder, and the one who
seems determined to prove himself. I have nothing to prove to you.

Colin

Bob-Stanton wrote:

wrote in message

Show me your model please.

Feel free to **** off, Bob!

You're the one who has the chip on his shoulder, and the one who
seems determined to prove himself. I have nothing to prove to you.

Colin

wrote in message ...
Bob-Stanton wrote:

wrote in message

Show me your model please.

Feel free to **** off, Bob!

You're the one who has the chip on his shoulder, and the one who
seems determined to prove himself. I have nothing to prove to you.



You have nothing to prove to me. OK, fine.

If you can't prove something, be honest and admit it. Don't hide
behind "I have nothing to prove to you."

Now I will "**** off". :-)

Bob Stanton

wrote in message ...
Bob-Stanton wrote:

wrote in message

Show me your model please.

Feel free to **** off, Bob!

You're the one who has the chip on his shoulder, and the one who
seems determined to prove himself. I have nothing to prove to you.



You have nothing to prove to me. OK, fine.

If you can't prove something, be honest and admit it. Don't hide
behind "I have nothing to prove to you."

Now I will "**** off". :-)

Bob Stanton

wrote in message ...
Bob-Stanton wrote:

wrote in message

Show me your model please.

Feel free to **** off, Bob!

You're the one who has the chip on his shoulder, and the one who
seems determined to prove himself. I have nothing to prove to you.



You have nothing to prove to me. OK, fine.

If you can't prove something, be honest and admit it. Don't hide
behind "I have nothing to prove to you."

Now I will "**** off". :-)

Bob Stanton

wrote in message ...
Bob-Stanton wrote:

wrote in message

Show me your model please.

Feel free to **** off, Bob!

You're the one who has the chip on his shoulder, and the one who
seems determined to prove himself. I have nothing to prove to you.



You have nothing to prove to me. OK, fine.

If you can't prove something, be honest and admit it. Don't hide
behind "I have nothing to prove to you."

Now I will "**** off". :-)

Bob Stanton

(Bob-Stanton) wrote in message
(Svante) wrote in message

OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.

I can send you a circuit analysis program that will do transmission
lines, if you want. It's an old DOS program, but it's works well.

Thank you for the offer, but I am the (perhaps silly) type of guy that
tries to understand things and make my own computer programs. I know
it is slower, but I feel that I learn from doing this.

I don't mind that sound arrives 100 ns late to my ears. This tells me
that RF models of cables ARE overkill (but applicable) and the great
margin tell me that simpler models probably would do OK. And even if a
really poor model would yield a delay of 1 ms, I would not mind.

How do you test to see if your computer model behaves like a real
cable? The quickest way and easiest way is the see if it has correct
delay. If a cable model doesn't predict the delay correctly, the
chances are it will not predict the impedance, or the frequeny
response correctly either.

Well, another way would be to take an ohm-meter and measure it's
resistance. That would be another aspect, that is VERY relevant. And
at least in my mind that is an easier measurement than the delay
measurement.

In my opinion, characteristic impedance and delay are unimportant in
the audio case.

Characteristic impedance, and cable length (delay), are all that are
needed for the prediction of rolloff at any frequencies, audio or RF.
The one caveat being that the R and G (conductances of the cable )
must be much lower than XL and XC of the cable.

Hmmm... So what is the typical XL/R ratio for audio frequencies? :-)
If that is a prerequisite, IS the transmission line model really valid
for audio frequencies?

What I wonder is if the transmission line model
predicts frequency response changes in the audio band (like a simple
RLC model does), given a frequency-varying load.

The transmission line model is accurate at audio frequenies. All
(real) loads vary with frequency. Circuit analysis programs are
designed to handle this.

Even in the case where the series resistance dominates, and the load
varies with frequency?

Anyway, how does the transmission line model you use work, actually?
Isn't it actually a large number of RLC elements connected in series
("one for each cm of the cable")?

The model uses no RLC elements.

The circuit analysis program looks that the cables's forward and
reverse transmission (gain and phase). It also looks at the
characteristic impedance, and the specified loss of the cable. From
this, it fiqures out the four scattering parameters of the cable
(easy). It converts these scattering pararmeters into Y parameters,
and then enters the Y-parameters into the circuit matrix as
conductances.

....and this you do for one frequency at a time, right? I mean, if you
want to do this for another frequency, you go through this process
again?

It is actually simpler for the computer to figure out the Y-parameters
of a transmission line, than it is to for it figure out the
Y-parameters of a resistor! You see, the resistor has series (lead)
inductance and parallel (body) capacitance. The computer must reduce
the complex resistor circuit down to two nodes before it enters the
resistor's conductance into the circuit matrix. It takes about as long
for computer to calculate a resistor's conductance, as it takes to
calculate a transmission line's conductance.

OK, but then I would argue that we are no longer talking about a
resistor, but a model of a real physical resistor, that contains other
elements as well. OK, I'm picky again.

Many people think that a transmission line model is overly complicated
(overkill). The computer thinks of the transmission line as simpler
than a single resistor. Ironic isn't it?

I'll have to think a bit about this to understand it. I have written
programs that reduced passive circuits down to 4-poles, but it was
some time ago. There were four types, G, Y, H and Z, was it? The H one
is often used to describe transistors, and the Y would be one of those
that you describe, right?

(Bob-Stanton) wrote in message
(Svante) wrote in message

OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.

I can send you a circuit analysis program that will do transmission
lines, if you want. It's an old DOS program, but it's works well.

Thank you for the offer, but I am the (perhaps silly) type of guy that
tries to understand things and make my own computer programs. I know
it is slower, but I feel that I learn from doing this.

I don't mind that sound arrives 100 ns late to my ears. This tells me
that RF models of cables ARE overkill (but applicable) and the great
margin tell me that simpler models probably would do OK. And even if a
really poor model would yield a delay of 1 ms, I would not mind.

How do you test to see if your computer model behaves like a real
cable? The quickest way and easiest way is the see if it has correct
delay. If a cable model doesn't predict the delay correctly, the
chances are it will not predict the impedance, or the frequeny
response correctly either.

Well, another way would be to take an ohm-meter and measure it's
resistance. That would be another aspect, that is VERY relevant. And
at least in my mind that is an easier measurement than the delay
measurement.

In my opinion, characteristic impedance and delay are unimportant in
the audio case.

Characteristic impedance, and cable length (delay), are all that are
needed for the prediction of rolloff at any frequencies, audio or RF.
The one caveat being that the R and G (conductances of the cable )
must be much lower than XL and XC of the cable.

Hmmm... So what is the typical XL/R ratio for audio frequencies? :-)
If that is a prerequisite, IS the transmission line model really valid
for audio frequencies?

What I wonder is if the transmission line model
predicts frequency response changes in the audio band (like a simple
RLC model does), given a frequency-varying load.

The transmission line model is accurate at audio frequenies. All
(real) loads vary with frequency. Circuit analysis programs are
designed to handle this.

Even in the case where the series resistance dominates, and the load
varies with frequency?

Anyway, how does the transmission line model you use work, actually?
Isn't it actually a large number of RLC elements connected in series
("one for each cm of the cable")?

The model uses no RLC elements.

The circuit analysis program looks that the cables's forward and
reverse transmission (gain and phase). It also looks at the
characteristic impedance, and the specified loss of the cable. From
this, it fiqures out the four scattering parameters of the cable
(easy). It converts these scattering pararmeters into Y parameters,
and then enters the Y-parameters into the circuit matrix as
conductances.

....and this you do for one frequency at a time, right? I mean, if you
want to do this for another frequency, you go through this process
again?

It is actually simpler for the computer to figure out the Y-parameters
of a transmission line, than it is to for it figure out the
Y-parameters of a resistor! You see, the resistor has series (lead)
inductance and parallel (body) capacitance. The computer must reduce
the complex resistor circuit down to two nodes before it enters the
resistor's conductance into the circuit matrix. It takes about as long
for computer to calculate a resistor's conductance, as it takes to
calculate a transmission line's conductance.

OK, but then I would argue that we are no longer talking about a
resistor, but a model of a real physical resistor, that contains other
elements as well. OK, I'm picky again.

Many people think that a transmission line model is overly complicated
(overkill). The computer thinks of the transmission line as simpler
than a single resistor. Ironic isn't it?

I'll have to think a bit about this to understand it. I have written
programs that reduced passive circuits down to 4-poles, but it was
some time ago. There were four types, G, Y, H and Z, was it? The H one
is often used to describe transistors, and the Y would be one of those
that you describe, right?

(Bob-Stanton) wrote in message
(Svante) wrote in message

OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.

I can send you a circuit analysis program that will do transmission
lines, if you want. It's an old DOS program, but it's works well.

Thank you for the offer, but I am the (perhaps silly) type of guy that
tries to understand things and make my own computer programs. I know
it is slower, but I feel that I learn from doing this.

I don't mind that sound arrives 100 ns late to my ears. This tells me
that RF models of cables ARE overkill (but applicable) and the great
margin tell me that simpler models probably would do OK. And even if a
really poor model would yield a delay of 1 ms, I would not mind.

How do you test to see if your computer model behaves like a real
cable? The quickest way and easiest way is the see if it has correct
delay. If a cable model doesn't predict the delay correctly, the
chances are it will not predict the impedance, or the frequeny
response correctly either.

Well, another way would be to take an ohm-meter and measure it's
resistance. That would be another aspect, that is VERY relevant. And
at least in my mind that is an easier measurement than the delay
measurement.

In my opinion, characteristic impedance and delay are unimportant in
the audio case.

Characteristic impedance, and cable length (delay), are all that are
needed for the prediction of rolloff at any frequencies, audio or RF.
The one caveat being that the R and G (conductances of the cable )
must be much lower than XL and XC of the cable.

Hmmm... So what is the typical XL/R ratio for audio frequencies? :-)
If that is a prerequisite, IS the transmission line model really valid
for audio frequencies?

What I wonder is if the transmission line model
predicts frequency response changes in the audio band (like a simple
RLC model does), given a frequency-varying load.

The transmission line model is accurate at audio frequenies. All
(real) loads vary with frequency. Circuit analysis programs are
designed to handle this.

Even in the case where the series resistance dominates, and the load
varies with frequency?

Anyway, how does the transmission line model you use work, actually?
Isn't it actually a large number of RLC elements connected in series
("one for each cm of the cable")?

The model uses no RLC elements.

The circuit analysis program looks that the cables's forward and
reverse transmission (gain and phase). It also looks at the
characteristic impedance, and the specified loss of the cable. From
this, it fiqures out the four scattering parameters of the cable
(easy). It converts these scattering pararmeters into Y parameters,
and then enters the Y-parameters into the circuit matrix as
conductances.

....and this you do for one frequency at a time, right? I mean, if you
want to do this for another frequency, you go through this process
again?

It is actually simpler for the computer to figure out the Y-parameters
of a transmission line, than it is to for it figure out the
Y-parameters of a resistor! You see, the resistor has series (lead)
inductance and parallel (body) capacitance. The computer must reduce
the complex resistor circuit down to two nodes before it enters the
resistor's conductance into the circuit matrix. It takes about as long
for computer to calculate a resistor's conductance, as it takes to
calculate a transmission line's conductance.

OK, but then I would argue that we are no longer talking about a
resistor, but a model of a real physical resistor, that contains other
elements as well. OK, I'm picky again.

Many people think that a transmission line model is overly complicated
(overkill). The computer thinks of the transmission line as simpler
than a single resistor. Ironic isn't it?

I'll have to think a bit about this to understand it. I have written
programs that reduced passive circuits down to 4-poles, but it was
some time ago. There were four types, G, Y, H and Z, was it? The H one
is often used to describe transistors, and the Y would be one of those
that you describe, right?

(Bob-Stanton) wrote in message
(Svante) wrote in message

OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.

I can send you a circuit analysis program that will do transmission
lines, if you want. It's an old DOS program, but it's works well.

Thank you for the offer, but I am the (perhaps silly) type of guy that
tries to understand things and make my own computer programs. I know
it is slower, but I feel that I learn from doing this.

I don't mind that sound arrives 100 ns late to my ears. This tells me
that RF models of cables ARE overkill (but applicable) and the great
margin tell me that simpler models probably would do OK. And even if a
really poor model would yield a delay of 1 ms, I would not mind.

How do you test to see if your computer model behaves like a real
cable? The quickest way and easiest way is the see if it has correct
delay. If a cable model doesn't predict the delay correctly, the
chances are it will not predict the impedance, or the frequeny
response correctly either.

Well, another way would be to take an ohm-meter and measure it's
resistance. That would be another aspect, that is VERY relevant. And
at least in my mind that is an easier measurement than the delay
measurement.

In my opinion, characteristic impedance and delay are unimportant in
the audio case.

Characteristic impedance, and cable length (delay), are all that are
needed for the prediction of rolloff at any frequencies, audio or RF.
The one caveat being that the R and G (conductances of the cable )
must be much lower than XL and XC of the cable.

Hmmm... So what is the typical XL/R ratio for audio frequencies? :-)
If that is a prerequisite, IS the transmission line model really valid
for audio frequencies?

What I wonder is if the transmission line model
predicts frequency response changes in the audio band (like a simple
RLC model does), given a frequency-varying load.

The transmission line model is accurate at audio frequenies. All
(real) loads vary with frequency. Circuit analysis programs are
designed to handle this.

Even in the case where the series resistance dominates, and the load
varies with frequency?

Anyway, how does the transmission line model you use work, actually?
Isn't it actually a large number of RLC elements connected in series
("one for each cm of the cable")?

The model uses no RLC elements.

The circuit analysis program looks that the cables's forward and
reverse transmission (gain and phase). It also looks at the
characteristic impedance, and the specified loss of the cable. From
this, it fiqures out the four scattering parameters of the cable
(easy). It converts these scattering pararmeters into Y parameters,
and then enters the Y-parameters into the circuit matrix as
conductances.

....and this you do for one frequency at a time, right? I mean, if you
want to do this for another frequency, you go through this process
again?

It is actually simpler for the computer to figure out the Y-parameters
of a transmission line, than it is to for it figure out the
Y-parameters of a resistor! You see, the resistor has series (lead)
inductance and parallel (body) capacitance. The computer must reduce
the complex resistor circuit down to two nodes before it enters the
resistor's conductance into the circuit matrix. It takes about as long
for computer to calculate a resistor's conductance, as it takes to
calculate a transmission line's conductance.

OK, but then I would argue that we are no longer talking about a
resistor, but a model of a real physical resistor, that contains other
elements as well. OK, I'm picky again.

Many people think that a transmission line model is overly complicated
(overkill). The computer thinks of the transmission line as simpler
than a single resistor. Ironic isn't it?

I'll have to think a bit about this to understand it. I have written
programs that reduced passive circuits down to 4-poles, but it was
some time ago. There were four types, G, Y, H and Z, was it? The H one
is often used to describe transistors, and the Y would be one of those
that you describe, right?

Don Pearce wrote in message . ..
On 10 Jan 2004 01:33:35 -0800, (Svante)
wrote:

Nowadays, it is quicker and easier (less typing) to enter a
transmission line model, than to type in a componet (L,C) model. Use
whatever way floats your boat.

OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.

You would have thought that given enough Ls and Cs (ie dividing the
lumped model very finely) you would end up with a perfect equivalent
of the transmission line model, but you don't. You just end up with an
ever steeper lowpass filter. Up to the cutoff point, this filter does
indeed behave remarkably like a true cable, though.

Yes, so the trick would be to use enough Ls and Cs then.

For much audio work a single L and C seem to do just fine, but there
are problems - like what order should you put them in? In theory you
can put the shunt C at either the start or end of the network, but if
you are modelling a very unmatched situation this won't work. For
example, if you are looking at an amplifier to a loudspeaker, the C
must be put at the speaker end - it has no effect on amplitude at the
amplifier end. In a matched scenario - equal impedances both ends, the
capacitance must be split and placed both ends if the model is to
work. So you must be careful in the application of a lumped model
cable, and understand the significance of the impedances at both ends
before you use it.

I'd think that either is OK as you increase the number of Ls and Cs.
This number will determine a highest valid frequency, and below that
frequency it does not matter much if analog starts with an L or a C.
When dealing with acoustic tubes I ususlly do it like this:

------L/2------*-----L/2-------
|
C
|
---------------*---------------

but one could also do:


-------*-----L------*----------
| |
C/2 C/2
| |
-------*------------*----------

Now, given that I have a high number of these sections, each of the
components will be small, and it will not matter much which model that
is used.


The true transmission line model has the advantage that all this is
taken care of, there is no anomalous lowpass filter effect to worry
about and it is really easy to change lengths - you just alter the
length term. It also works at any frequency. It is a sledgehammer to
crack a nut, though, and representing a cable as Ls and Cs (given the
caveats above) is perfectly proper, particularly if you are having to
hand-crank the results, or just doing a back-of-an-envelope
calculation. If you are using Spice, or something similar that
possesses native transmission line models, then why not use them? They
are easier to use, just as accurate for audio, and vastly more
accurate outside the audio band.

I can understand that this COULD be the case, but I don't understand
it (yet). I guess I'll just have to learn it.

Don Pearce wrote in message . ..
On 10 Jan 2004 01:33:35 -0800, (Svante)
wrote:

Nowadays, it is quicker and easier (less typing) to enter a
transmission line model, than to type in a componet (L,C) model. Use
whatever way floats your boat.

OK, in my boat there are no transmission line models, but a lot of R,
L and Cs.

You would have thought that given enough Ls and Cs (ie dividing the
lumped model very finely) you would end up with a perfect equivalent
of the transmission line model, but you don't. You just end up with an
ever steeper lowpass filter. Up to the cutoff point, this filter does
indeed behave remarkably like a true cable, though.

Yes, so the trick would be to use enough Ls and Cs then.

For much audio work a single L and C seem to do just fine, but there
are problems - like what order should you put them in? In theory you
can put the shunt C at either the start or end of the network, but if
you are modelling a very unmatched situation this won't work. For
example, if you are looking at an amplifier to a loudspeaker, the C
must be put at the speaker end - it has no effect on amplitude at the
amplifier end. In a matched scenario - equal impedances both ends, the
capacitance must be split and placed both ends if the model is to
work. So you must be careful in the application of a lumped model
cable, and understand the significance of the impedances at both ends
before you use it.

I'd think that either is OK as you increase the number of Ls and Cs.
This number will determine a highest valid frequency, and below that
frequency it does not matter much if analog starts with an L or a C.
When dealing with acoustic tubes I ususlly do it like this:

------L/2------*-----L/2-------
|
C
|
---------------*---------------

but one could also do:


-------*-----L------*----------
| |
C/2 C/2
| |
-------*------------*----------

Now, given that I have a high number of these sections, each of the
components will be small, and it will not matter much which model that
is used.


The true transmission line model has the advantage that all this is
taken care of, there is no anomalous lowpass filter effect to worry
about and it is really easy to change lengths - you just alter the
length term. It also works at any frequency. It is a sledgehammer to
crack a nut, though, and representing a cable as Ls and Cs (given the
caveats above) is perfectly proper, particularly if you are having to
hand-crank the results, or just doing a back-of-an-envelope
calculation. If you are using Spice, or something similar that
possesses native transmission line models, then why not use them? They
are easier to use, just as accurate for audio, and vastly more
accurate outside the audio band.

I can understand that this COULD be the case, but I don't understand
it (yet). I guess I'll just have to learn it.