In article , Rob
wrote:
Jim Lesurf wrote:
Hi,

I've just put up a new webpage that provides some measurements on the
properties of a variety of loudspeaker cables. The page is at

http://www.audiomisc.co.uk/HFN/Cables3/TakeTheLead.html

It is an expanded version of the article published in 'Hi Fi News' a
few months ago.

Slainte,

Jim


FWIW it means very little to me. You seem to assume a correlation
between frequency, resistance and sound.

Not sure what you mean, I'm afraid.


Perhaps a paragraph or two on what you might expect any measured result
in the context of your measurments to mean?

The measurements and results serve two purposes.

1) The size of the peaks and dips in impedance will vary with the choice of
cable and end-load (speaker). Using 'open' and 'short' means loads with
impedances as high and low as you can get compared with the cable
impedance. So you can expect the results to give you a guide to which
cables give the highest or lowest peaks/dips for real-world loads. Hence
the results give a sign of which cables would be more risky with amplifiers
that are not unconditionally stable, or whose behaviour can be upset by RF
resonances, etc. In particular, sharp dips down to very low impedance can
be bad news for a poor amplifier. Hence useful as a warning.

2) You can use the measured impedances as a function of frequency to
determine the electrical properties of the cables. Choice of 'open' and
'short' here makes calculating the cable properties simpler, although in
principle any two choices of loading with significantly different values
would do. In the absence of a the amp having an RF problem these values are
most useful for telling you the cable series resistance and inductance as a
function of frequency in the audio band. (Yes, both values can vary with
frequency, although probably not by much in the audio band.) Combined with
the loudspeaker impedance, these series values change the frequency
response in the audible range. So the values determined from the RF data
tell you something about what changes to expect in the *audio* frequency
response. In particular, you want low series inductance and resistance to
minimise alterations in frequency response in most cases. The snag is that
*very* low inductance, in our universe, means *high* shunt capacitance
which can change the response from amps that have an output series
inductor. (Which I would recommend they *do* have.)

I've certainly known about all the above for decades. It was taken as
standard knowledge by people I've worked with. Although I guess some
audio-only designers may not know how the cable properties can be measured
using a VNA in this manner, but it isn't unusual in RF/microwave
engineering.

There are a couple of follow-on articles, that do look at this further, and
include simple techniques - like the use of a series inductor and 'zobel'
on the amp to help protect it against (1). That is a method I've always
used as it works neatly. But there are commercial amplifier designs that
*don't* do this, so are exposed to RF loading by the cable and speaker. And
the use of a series inductor may mean you'd have to be wary of ultra-low
inductance cables for the perverse reason that they have ultra-high shunt
capacitance.

Slainte,

Jim

--
Please use the address on the audiomisc page 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

Jim Lesurf wrote:
In article , Rob
wrote:
Jim Lesurf wrote:
Hi,

I've just put up a new webpage that provides some measurements on the
properties of a variety of loudspeaker cables. The page is at

http://www.audiomisc.co.uk/HFN/Cables3/TakeTheLead.html

It is an expanded version of the article published in 'Hi Fi News' a
few months ago.

Slainte,

Jim


FWIW it means very little to me. You seem to assume a correlation
between frequency, resistance and sound.

Not sure what you mean, I'm afraid.


There's a relationship between three things: frequency and resistance
(the things you plot) and sound. If one of the things change, another
one will change ('correlation'). On further reading you suggest a
relationship between frequency, resistance and risk.


Perhaps a paragraph or two on what you might expect any measured result
in the context of your measurments to mean?

The measurements and results serve two purposes.

1) The size of the peaks and dips in impedance will vary with the choice of
cable and end-load (speaker). Using 'open' and 'short' means loads with
impedances as high and low as you can get compared with the cable
impedance. So you can expect the results to give you a guide to which
cables give the highest or lowest peaks/dips for real-world loads. Hence
the results give a sign of which cables would be more risky with amplifiers
that are not unconditionally stable, or whose behaviour can be upset by RF
resonances, etc. In particular, sharp dips down to very low impedance can
be bad news for a poor amplifier. Hence useful as a warning.


Ah, OK, good. But is it *really* risky for any amplifier that doesn't
carry a cable recommendation tag? By risk I assume possibility of
component failure.

2) You can use the measured impedances as a function of frequency to
determine the electrical properties of the cables. Choice of 'open' and
'short' here makes calculating the cable properties simpler, although in
principle any two choices of loading with significantly different values
would do. In the absence of a the amp having an RF problem these values are
most useful for telling you the cable series resistance and inductance as a
function of frequency in the audio band. (Yes, both values can vary with
frequency, although probably not by much in the audio band.) Combined with
the loudspeaker impedance, these series values change the frequency
response in the audible range. So the values determined from the RF data
tell you something about what changes to expect in the *audio* frequency
response. In particular, you want low series inductance and resistance to
minimise alterations in frequency response in most cases. The snag is that
*very* low inductance, in our universe, means *high* shunt capacitance
which can change the response from amps that have an output series
inductor. (Which I would recommend they *do* have.)


It'd be nice, although I expect quite difficult, if you could explain
how these effects could influence sound.

I've certainly known about all the above for decades. It was taken as
standard knowledge by people I've worked with. Although I guess some
audio-only designers may not know how the cable properties can be measured
using a VNA in this manner, but it isn't unusual in RF/microwave
engineering.

There are a couple of follow-on articles, that do look at this further, and
include simple techniques - like the use of a series inductor and 'zobel'
on the amp to help protect it against (1). That is a method I've always
used as it works neatly. But there are commercial amplifier designs that
*don't* do this, so are exposed to RF loading by the cable and speaker.

Sounds daft. Do you know which amplifiers?

And
the use of a series inductor may mean you'd have to be wary of ultra-low
inductance cables for the perverse reason that they have ultra-high shunt
capacitance.


Excellent! It's clear that the technically literate here know what
you're driving at, and if Maplin's own is good enough for you etc :-)

Rob

In article , Rob
wrote:
Jim Lesurf wrote:

FWIW it means very little to me. You seem to assume a correlation
between frequency, resistance and sound.

Not sure what you mean, I'm afraid.


There's a relationship between three things: frequency and resistance
(the things you plot) and sound.

All the plots show relationships between frequency and apparent load
'resistance' (actually magnitude of impedance). But that isn't directly
related to 'sound' as such.


If one of the things change, another one will change ('correlation'). On
further reading you suggest a relationship between frequency, resistance
and risk.

As above. Sharp/deep dips in the 'resistance' as you change frequency tend
to give more 'risk' that the amplifier will be affected in a significant
manner. But this isn't a simple relationship with 'risk' as that depends on
'risk of what' and choice of amp, etc. Decent amplifier designs will be
essentially unaffected by all this. But some amps might be unhappy.


Perhaps a paragraph or two on what you might expect any measured
result in the context of your measurments to mean?

The measurements and results serve two purposes.

1) The size of the peaks and dips in impedance will vary with the
choice of cable and end-load (speaker). Using 'open' and 'short' means
loads with impedances as high and low as you can get compared with the
cable impedance. So you can expect the results to give you a guide to
which cables give the highest or lowest peaks/dips for real-world
loads. Hence the results give a sign of which cables would be more
risky with amplifiers that are not unconditionally stable, or whose
behaviour can be upset by RF resonances, etc. In particular, sharp
dips down to very low impedance can be bad news for a poor amplifier.
Hence useful as a warning.


Ah, OK, good. But is it *really* risky for any amplifier that doesn't
carry a cable recommendation tag? By risk I assume possibility of
component failure.

It is certainly possible for an amplifier to exhibit uncontrolled RF
oscillations, and for those to then damage the amplifier. Possibly also the
speaker. But I can't tell you any value for the 'risk' of this happening as
it would depend on things we don't know. More likely is that the audio
behaviour may be affected without the amp failing.

Again, well designed amplifiers aren't at any 'risk'. If the designer knew
what he was doing they will be stable into any load.

[snip]

It'd be nice, although I expect quite difficult, if you could explain
how these effects could influence sound.

Again, depends on the circumstances. High cable series impedance will alter
the frequency response in ways that depend on your choice of speaker.

High cable shunt capacitance may affect response if the amp has a high
output impedance (very low 'damping factor').

But the details will depend on the specific case. The alterations may be
too small to be bothered with, or not...


There are a couple of follow-on articles, that do look at this
further, and include simple techniques - like the use of a series
inductor and 'zobel' on the amp to help protect it against (1). That
is a method I've always used as it works neatly. But there are
commercial amplifier designs that *don't* do this, so are exposed to
RF loading by the cable and speaker.

Sounds daft. Do you know which amplifiers?

I can't comment on any current or recent commercial designs as I've not
measured them, and reviews generally ignore this area. So no data. I think
it likely that most (indeed almost all) are fine as this should be a known
problem, and engineers determined how to fix it decades ago. Maybe they are
all fine. But... no data.

However I do tend to get an uneasy feeling when reviews ignore issues like
this for decades. It can mean eyes are not on the ball and problems
familiar to past generations of engineers may end up in new designs because
no-one is alert. I confess I do wonder when I see some of the more 'quirky'
designs sold at high prices that have all kinds of of characteristics.

I can only say that I've personally seen such effects in amps many years
ago. e.g. in the Naim amps of some decades ago. It is a common problem with
experimental designs which the designer then has to iron out.

The problem here is that it can make good sense to choose loudspeaker
cables with very low series resistance and inductance, but that this means
high capacitance with minimal damping losses, and unless the amplifier is
happy with this there may be drawbacks.

In our universe, the product of series inductance and shunt capacitance for
cables is limited by the speed of light. Lowering one tends to shove up the
other. To avoid this, invent warp drive, or use a wormhole in space for the
cable. ...or just keep down the length of cable needed. :-)

Slainte,

Jim

--
Please use the address on the audiomisc page 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

Jim Lesurf wrote:
In article , Rob
wrote:
Jim Lesurf wrote:

FWIW it means very little to me. You seem to assume a correlation
between frequency, resistance and sound.
Not sure what you mean, I'm afraid.


There's a relationship between three things: frequency and resistance
(the things you plot) and sound.

All the plots show relationships between frequency and apparent load
'resistance' (actually magnitude of impedance). But that isn't directly
related to 'sound' as such.


Ah fine, that was just my assumption relating to the point of the
article. I see now the point of your discussion is 'risk'. Or have I got
this wrong? There was no specific point - just a series of tests to see
what happens?

If one of the things change, another one will change ('correlation'). On
further reading you suggest a relationship between frequency, resistance
and risk.

As above. Sharp/deep dips in the 'resistance' as you change frequency tend
to give more 'risk' that the amplifier will be affected in a significant
manner. But this isn't a simple relationship with 'risk' as that depends on
'risk of what' and choice of amp, etc. Decent amplifier designs will be
essentially unaffected by all this. But some amps might be unhappy.

Perhaps a paragraph or two on what you might expect any measured
result in the context of your measurments to mean?
The measurements and results serve two purposes.

1) The size of the peaks and dips in impedance will vary with the
choice of cable and end-load (speaker). Using 'open' and 'short' means
loads with impedances as high and low as you can get compared with the
cable impedance. So you can expect the results to give you a guide to
which cables give the highest or lowest peaks/dips for real-world
loads. Hence the results give a sign of which cables would be more
risky with amplifiers that are not unconditionally stable, or whose
behaviour can be upset by RF resonances, etc. In particular, sharp
dips down to very low impedance can be bad news for a poor amplifier.
Hence useful as a warning.


Ah, OK, good. But is it *really* risky for any amplifier that doesn't
carry a cable recommendation tag? By risk I assume possibility of
component failure.

It is certainly possible for an amplifier to exhibit uncontrolled RF
oscillations, and for those to then damage the amplifier. Possibly also the
speaker. But I can't tell you any value for the 'risk' of this happening as
it would depend on things we don't know. More likely is that the audio
behaviour may be affected without the amp failing.


I'm sorry - lost here. You explained above that the relationships you
are examining are not related to sound 'as such'. Does 'as such' mean
'except when it is'? ;-)

I know you don't know everything about every amplifier, but could you
explain what the average punter should look for in an amplifier to avoid
these issues? The sorts of questions I can ask a manufacturer for example?

Again, well designed amplifiers aren't at any 'risk'. If the designer knew
what he was doing they will be stable into any load.

[snip]

It'd be nice, although I expect quite difficult, if you could explain
how these effects could influence sound.

Again, depends on the circumstances. High cable series impedance will alter
the frequency response in ways that depend on your choice of speaker.

High cable shunt capacitance may affect response if the amp has a high
output impedance (very low 'damping factor').

But the details will depend on the specific case. The alterations may be
too small to be bothered with, or not...


I know of course this is going completely left field, but could you give
real world examples (*an* amplifier*, *some* cable) when sound might be
affected? I suspect your interest is entirely theoretical, but and if I
may say you do appear reluctant to be drawn . . .

A *useful* theory is one that explains why something is happening. I
follow your theory development to a point, but I don't understand what
use your findings are (exception noted below, remove possibility of
problems) if they're not 'latched' on to real world scenarios.

There are a couple of follow-on articles, that do look at this
further, and include simple techniques - like the use of a series
inductor and 'zobel' on the amp to help protect it against (1). That
is a method I've always used as it works neatly. But there are
commercial amplifier designs that *don't* do this, so are exposed to
RF loading by the cable and speaker.

Sounds daft. Do you know which amplifiers?

I can't comment on any current or recent commercial designs as I've not
measured them, and reviews generally ignore this area. So no data. I think
it likely that most (indeed almost all) are fine as this should be a known
problem, and engineers determined how to fix it decades ago. Maybe they are
all fine. But... no data.

However I do tend to get an uneasy feeling when reviews ignore issues like
this for decades. It can mean eyes are not on the ball and problems
familiar to past generations of engineers may end up in new designs because
no-one is alert. I confess I do wonder when I see some of the more 'quirky'
designs sold at high prices that have all kinds of of characteristics.

I can only say that I've personally seen such effects in amps many years
ago. e.g. in the Naim amps of some decades ago. It is a common problem with
experimental designs which the designer then has to iron out.

The problem here is that it can make good sense to choose loudspeaker
cables with very low series resistance and inductance, but that this means
high capacitance with minimal damping losses, and unless the amplifier is
happy with this there may be drawbacks.


Yes, I think *that's* a good point - remove the possibility of trouble
ahead, however remote that possibility.

In our universe, the product of series inductance and shunt capacitance for
cables is limited by the speed of light. Lowering one tends to shove up the
other. To avoid this, invent warp drive, or use a wormhole in space for the
cable. ...or just keep down the length of cable needed. :-)


Noted :-)

Rob

Jim Lesurf wrote:

Rob wrote:
Jim Lesurf wrote:

FWIW it means very little to me. You seem to assume a correlation
between frequency, resistance and sound.

Not sure what you mean, I'm afraid.

That much is apparent. Doubt you know much about the concept at all, nor the
bases of stability.

Graham


--
due to the hugely increased level of spam please make the obvious adjustment to
my email address

"Eeyore" wrote in message
...


Not sure what you mean, I'm afraid.

That much is apparent. Doubt you know much about the concept at all, nor
the
bases of stability.


I wonder why it is that some people on this NG post simply to be offensive
to others? Of *course* Jim knows the basis of stability, at least as well
as you do, probably a lot better.

David.

On 8 Aug, 20:13, "David Looser" wrote:
"Eeyore" wrote in message

...



Not sure what you mean, I'm afraid.

That much is apparent. Doubt you know much about the concept at all, nor
the
bases of stability.

I wonder why it is that some people on this NG post simply to be offensive
to others? Of **course* Jim knows the basis of stability, at least as well
as you do, probably a lot better.

David.

Indeed, you'd hope that he does, given that he teaches degree-level
courses in the subject. Now, let's remind ourselves what the lovely
Graham actually does........

David Looser wrote:

"Eeyore" wrote

Not sure what you mean, I'm afraid.

That much is apparent. Doubt you know much about the concept at all, nor
the bases of stability.

I wonder why it is that some people on this NG post simply to be offensive
to others? Of *course* Jim knows the basis of stability, at least as well
as you do, probably a lot better.

Not if he thinks the answer belongs in the CABLE ! That's pure humbug.

JHC !

Graham

--
due to the hugely increased level of spam please make the obvious adjustment
to my email address

On Sat, 08 Aug 2009 19:58:06 +0100, Eeyore
wrote:



Jim Lesurf wrote:

Rob wrote:
Jim Lesurf wrote:

FWIW it means very little to me. You seem to assume a correlation
between frequency, resistance and sound.

Not sure what you mean, I'm afraid.

That much is apparent. Doubt you know much about the concept at all, nor the
bases of stability.


Can you explain then? It has me puzzled too. And given Jim's
background I am going to tell you he knows precisely what stability
means, and how to measure and predict it.

Stability circles are the second thing you learn about on the Smith
Chart.

d

In article 4a800142.407830593@localhost, Don Pearce
wrote:
On Sat, 08 Aug 2009 19:58:06 +0100, Eeyore
wrote:



Jim Lesurf wrote:

Rob wrote:
Jim Lesurf wrote:

FWIW it means very little to me. You seem to assume a correlation
between frequency, resistance and sound.

Not sure what you mean, I'm afraid.

That much is apparent. Doubt you know much about the concept at all,
nor the bases of stability.


Can you explain then? It has me puzzled too. And given Jim's background
I am going to tell you he knows precisely what stability means, and how
to measure and predict it.

I guess I have had to deal with this in more ways than many engineers. From
designing audio power amps that were unconditionally stable to 90-300 GHz
oscillators where the precise details of the instability were critical to
the performance. :-)

I now wonder if some audio engineers simply aren't familiar with the
methods that are normal in RF/microwave.

Slainte,

Jim

--
Please use the address on the audiomisc page 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