On Tue, 13 Nov 2007 10:53:08 GMT, Bob Latham
wrote:

A couple of decades ago, I got my hands on some quite substantial screened
cable that had been ripped out of a repeater station. The cable had two
separate insulated conductors inside a single overall screen. I used the
two conductors as signal and ground and connected both at both ends. The
screen, I only connected at one end as I thought this would mean no
current could flow in the screen, it would just be a screen.

Okay, I'll state the obvious. This arrangement was very directional. Yes,
I could tell which way around it was walking into the room with no prior
knowledge and so could everyone else there at the time.

I know there is a non magical explanation but I've not heard one yet that
I can get my head around.


What was the audible difference?

In article , Bob Latham
wrote:
In article , Don Pearce
wrote:
On Tue, 13 Nov 2007 10:53:08 GMT, Bob Latham
wrote:

Okay, I'll state the obvious. This arrangement was very directional.
Yes, I could tell which way around it was walking into the room with
no prior knowledge and so could everyone else there at the time.

Do you mean you could hear mains hum when it was the wrong way round,
or the musical sound was in some way changed?

There was no hum, it was well screened and properly connected and no
earth loop problem.

The problem here is twofold.

Firstly, that it is unlikely that there was literally "no hum". Almost
certain in a mains-based system that there would be a non-zero amount at
50H and/or harmonics.

Secondly, that low levels of steady LF like 50Hz isn't necessarily heard as
an audible note. It can have the effect of being like a slight 'pressure'
or 'feeling' which can then affect your perception in a way you identify in
another way. Part of the reason is the way our hearing adapts to low level
continuous stimulii. Our systems tend to focus on sudden changes and tend
to acclimatise to steady levels if they are modest/small.

So I'd be surprised if changing which end the screen was grounded made no
difference at all to the hum level. What might well be true is that in both
cases it was too low to be noticed.

The cable direction didn't seem to have any noticeable effect on tonal
balance though it may have made subtle changes I didn't notice. What it
did do was change the sound stage image. In one direction there was no
depth to the sound stage, in the other it was very good. I know I'll not
be believed but this was far from subtle this was seriously obvious.

I have more than once had a similar impression which I've learned to
identify as a sign that there is some low level continuous LF. In some
cases this is hum from the audio system. But in other cases it is something
like rumble or something like a motor in a heating system elsewhere in the
house.

The
impression I got at the time was that the female singer moved about 3
feet backwards or forwards depending on the direction of the cable.

I've never heard anything so obvious before or since, I don't think it
was magic but I would like to understand what was happening. I almost
wish I'd kept the cables now but at the time I didn't wish to be accused
of copper theft from the skip and so put the cables back after the
weekend.

In cases like the one described, changing which end of the cable is used to
ground the screen can alter the hum level. I have no idea if this was the
reason for what you describe, but it seems at least plausible to me as a
possible reason.

In some extreme cases any common ground resistance could also affect the
crosstalk, and thus the image. But I'd regard that as less likely as the
required level of common-mode resistance is probably too high to crop up in
a decent domestic system.

Slainte,

Jim

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Bob Latham wrote:
In article ,
Don Pearce wrote:
On Tue, 13 Nov 2007 10:12:28 +0000, Nick Gorham
wrote:

The other time they may be "endian" is a phono to phono where the
screen is only connected to the plug at one end on the cable.

Even then I'm not convinced. The reason you would use such a lead is
when you already have a ground connection at each end and you want to
avoid creating a ground loop. That being the case, the grounds at both
ends of the cable are equally valid, and there is no reason to connect
the cable one way rather than the other.

Is there another explanation that casts light?

I've have related this tale before but I would still like to understand
the mechanism.

A couple of decades ago, I got my hands on some quite substantial screened
cable that had been ripped out of a repeater station. The cable had two
separate insulated conductors inside a single overall screen. I used the
two conductors as signal and ground and connected both at both ends. The
screen, I only connected at one end as I thought this would mean no
current could flow in the screen, it would just be a screen.

Okay, I'll state the obvious. This arrangement was very directional. Yes,
I could tell which way around it was walking into the room with no prior
knowledge and so could everyone else there at the time.

I know there is a non magical explanation but I've not heard one yet that
I can get my head around.


I can't explain I'm afraid - but a NAD tec advised retain the ground at
the source, and open at the other end. He did offer an explanation, and
IIRC it had the phrase 'earth loop', but that was about all I took in.
And it worked. In fact QED market cables with this characteristic.

"Don Pearce" wrote in message
...

This would normally be considered a microphone cable. I have to say
though that when I had to rewire a TV control room in Qatar, with the
slight requirement that I wasn't allowed to put it off the air, or
lose sound for longer than five seconds, I did all the line level
wiring in balanced screened twin. But that was in a very noisy
electrical environment. I can't see it doing much domestically.


Line-level audio in a TV control room would be balanced as a matter of
course, so you wouldn't have had any option *but* to use balanced twin
screened cable.

David.

"Rob" wrote in message
...

I can't explain I'm afraid - but a NAD tec advised retain the ground at
the source, and open at the other end. He did offer an explanation, and
IIRC it had the phrase 'earth loop', but that was about all I took in. And
it worked. In fact QED market cables with this characteristic.

In medicine the "placebo effect" is well known. Give someone a "cure" which
is, of itself, worthless, but convince them that it will cure them, and it
works!, far better than chance. ISTM that there is a similar effect in HiFi.
Tell someone that you have a gadget that will dramatically improve the sound
of their system, make them buy-in to the idea (preferably by relieving them
of a lot of money for it) and they really will hear a difference even though
the gadget itself is of no real value. This is why double-blind trials are
just as important in assessing the sonic qualities of HiFi components as it
is in testing new drugs.

David.

On Tue, 13 Nov 2007 17:10:46 -0000, "David Looser"
wrote:

"Don Pearce" wrote in message
...

This would normally be considered a microphone cable. I have to say
though that when I had to rewire a TV control room in Qatar, with the
slight requirement that I wasn't allowed to put it off the air, or
lose sound for longer than five seconds, I did all the line level
wiring in balanced screened twin. But that was in a very noisy
electrical environment. I can't see it doing much domestically.


Line-level audio in a TV control room would be balanced as a matter of
course, so you wouldn't have had any option *but* to use balanced twin
screened cable.

David.


You'd have thought. All the equipment was balanced, but all the cable
was coax. It was causing unbelievable problems. Some cowboy obviously
had a van load of the stuff when he wired the place up.

d

--
Pearce Consulting
http://www.pearce.uk.com

"Don Pearce" wrote in message
...
On Tue, 13 Nov 2007 17:10:46 -0000, "David Looser"
wrote:

"Don Pearce" wrote in message
...

This would normally be considered a microphone cable. I have to say
though that when I had to rewire a TV control room in Qatar, with the
slight requirement that I wasn't allowed to put it off the air, or
lose sound for longer than five seconds, I did all the line level
wiring in balanced screened twin. But that was in a very noisy
electrical environment. I can't see it doing much domestically.


Line-level audio in a TV control room would be balanced as a matter of
course, so you wouldn't have had any option *but* to use balanced twin
screened cable.

David.


You'd have thought. All the equipment was balanced, but all the cable
was coax. It was causing unbelievable problems. Some cowboy obviously
had a van load of the stuff when he wired the place up.

Cowboy is the word!, no wonder you need to re-wire the place :-)

David.

David Looser wrote:
"Rob" wrote in message
...
I can't explain I'm afraid - but a NAD tec advised retain the ground at
the source, and open at the other end. He did offer an explanation, and
IIRC it had the phrase 'earth loop', but that was about all I took in. And
it worked. In fact QED market cables with this characteristic.

In medicine the "placebo effect" is well known. Give someone a "cure" which
is, of itself, worthless, but convince them that it will cure them, and it
works!, far better than chance. ISTM that there is a similar effect in HiFi.
Tell someone that you have a gadget that will dramatically improve the sound
of their system, make them buy-in to the idea (preferably by relieving them
of a lot of money for it) and they really will hear a difference even though
the gadget itself is of no real value. This is why double-blind trials are
just as important in assessing the sonic qualities of HiFi components as it
is in testing new drugs.

David.


The effect was clear and audible absence of audible hum. I don't think
even you would need a double blind test to establish something quite so
obvious.

"Rob" wrote in message
...
David Looser wrote:
"Rob" wrote in message
...
I can't explain I'm afraid - but a NAD tec advised retain the ground at
the source, and open at the other end. He did offer an explanation, and
IIRC it had the phrase 'earth loop', but that was about all I took in.
And it worked. In fact QED market cables with this characteristic.

In medicine the "placebo effect" is well known. Give someone a "cure"
which is, of itself, worthless, but convince them that it will cure them,
and it works!, far better than chance. ISTM that there is a similar
effect in HiFi. Tell someone that you have a gadget that will
dramatically improve the sound of their system, make them buy-in to the
idea (preferably by relieving them of a lot of money for it) and they
really will hear a difference even though the gadget itself is of no real
value. This is why double-blind trials are just as important in
assessing the sonic qualities of HiFi components as it is in testing new
drugs.

David.


The effect was clear and audible absence of audible hum. I don't think
even you would need a double blind test to establish something quite so
obvious.

I thought you were saying that QED were selling special (and presumably
expensive) cables?

But I would not advise disconnecting the signal ground at one end of the
audio lead to cure ground-loop hum, as the signal return then has to find
it's way back via a poorly defined ground path which can lead to all sorts
of other interference
or crosstalk.

I'd want to look at a system to estasblish why there was a ground-loop in
the first place. Is it due to earth cores in mains cables?, or to other
audio paths?. If the former disconnect the offending earth wires, if the
later bundle the audio cables together so that there is no space between
them for 50Hz magnetic fields to penetrate.

David.

"Signal" wrote in message
...
"David Looser" wrote:

I can't explain I'm afraid - but a NAD tec advised retain the ground at
the source, and open at the other end. He did offer an explanation, and
IIRC it had the phrase 'earth loop', but that was about all I took in.
And
it worked. In fact QED market cables with this characteristic.

In medicine the "placebo effect" is well known. Give someone a "cure"
which
is, of itself, worthless, but convince them that it will cure them, and it
works!, far better than chance. ISTM that there is a similar effect in
HiFi.
Tell someone that you have a gadget that will dramatically improve the
sound
of their system, make them buy-in to the idea (preferably by relieving
them
of a lot of money for it) and they really will hear a difference even
though
the gadget itself is of no real value.

This is pretty offensive. You speak as if most people are totally
gullible ****s.. actually such people are few and far between. The
difference between a placebo and real audio difference is the former
changes **** ALL. Most people have a sense of proportion, and do not
ceaselessly chase differences that are imperceptible. Plus, anyone
with a modicum of hifi/listening experience is able to reasonably
determine the gray area in their perception, if they haven't been
persuaded otherwise by people like yourself.

This is why double-blind trials are
just as important in assessing the sonic qualities of HiFi components as
it
is in testing new drugs.

Well I don't like to draw direct analogies between drug and hifi blind
tests (which are far from equivalent), but yes the underlying
principle is nice in theory. However, pertaining to controversial
areas of hifi, there are practically no DBTs of a grade which could be
called conclusive. I worked on a multi-million double blind clinical
trial at ICI, and by comparison the majority of audio DBTs I've heard
about are laughable. Basically virtually nobody outside of R&D has the
funding or indeed inclination to do these tests to a very high
standard. Until such times, the results of these tests should be taken
with a very large pinch of salt.. and remember, it's possible to be
influenced by propaganda in the opposite direction too!





--
S i g n a l @ l i n e o n e . n e t

If, as you say, gullible ****s are few and far between, how does that
account for the continuance in business of, amongst others, Russ Andrews,
who's entire stock in trade depends on such gullibility?

S.



--
http://audiopages.googlepages.com