[Gareth Magennis]

Hi,

something I've never really been sure about:

Say you have a control room and a live room connected with a single
multicore, down which you will have your mic feeds and will also be sending
headphone feeds back.
I've always assumed it would be far better to have the headphone amps in the
live room, as sending "power" down the multicore may induce crosstalk into
the mic feeds, where sending just the signal may not.

Is this actually the case? The voltage in a powered headphone feed is
presumably comparable-ish with line levels, but obviously carries current.
Does that current make crosstalk more likely?


Cheers,


Gareth.

[Scott Dorsey]

Gareth Magennis wrote:

Say you have a control room and a live room connected with a single
multicore, down which you will have your mic feeds and will also be sending
headphone feeds back.
I've always assumed it would be far better to have the headphone amps in the
live room, as sending "power" down the multicore may induce crosstalk into
the mic feeds, where sending just the signal may not.

Is this actually the case? The voltage in a powered headphone feed is
presumably comparable-ish with line levels, but obviously carries current.
Does that current make crosstalk more likely?

The increased current isn't a big deal but....

1. it's not a balanced signal. It's two unbalanced lines wrapped into the
same pair, so anything that isn't common to both channels will be radiating
some magnetic field.

2. Because the headphone impedance is lower than a 600 ohm balanced in, there
will be more signal loss due to resistance in the cable, and the frequency
response of the headphones will be changed since they'll be seeing a higher
impedance source.


And really, #2 is the big one. Run the amps at the end, or run some big
14 awg cable to your headphone distribution box.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Richard Webb[_3_]]

On Wed 2011-Oct-12 19:27, Scott Dorsey writes:
I've always assumed it would be far better to have the headphone amps in the
live room, as sending "power" down the multicore may induce crosstalk into
the mic feeds, where sending just the signal may not.
snip

The increased current isn't a big deal but....

1. it's not a balanced signal. It's two unbalanced lines wrapped
into the same pair, so anything that isn't common to both
channels will be radiating some magnetic field.

Agreed, might, or might not be a concern.

2. Because the headphone impedance is lower than a 600 ohm balanced
in, there will be more signal loss due to resistance in the
cable, and the frequency response of the headphones will be
changed since they'll be seeing a higher impedance source.


wEll stated.

And really, #2 is the big one. Run the amps at the end, or run some
big 14 awg cable to your headphone distribution box.
I like running the amps at the end near the headphones, use
two balanced pairs in the multicore to run my line level
signal to the amps from the control room. This has always
been my preferred approach.

Regards,
Richard
--
| Remove .my.foot for email
| via Waldo's Place USA Fidonet-Internet Gateway Site
| Standard disclaimer: The views of this user are strictly his own.

[Gareth Magennis]

"Scott Dorsey" wrote in message
...
Gareth Magennis wrote:

Say you have a control room and a live room connected with a single
multicore, down which you will have your mic feeds and will also be
sending
headphone feeds back.
I've always assumed it would be far better to have the headphone amps in
the
live room, as sending "power" down the multicore may induce crosstalk into
the mic feeds, where sending just the signal may not.

Is this actually the case? The voltage in a powered headphone feed is
presumably comparable-ish with line levels, but obviously carries
current.
Does that current make crosstalk more likely?

The increased current isn't a big deal but....

1. it's not a balanced signal. It's two unbalanced lines wrapped into the
same pair, so anything that isn't common to both channels will be
radiating
some magnetic field.

2. Because the headphone impedance is lower than a 600 ohm balanced in,
there
will be more signal loss due to resistance in the cable, and the
frequency
response of the headphones will be changed since they'll be seeing a
higher
impedance source.


And really, #2 is the big one. Run the amps at the end, or run some big
14 awg cable to your headphone distribution box.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


Thanks Scott, no. 1 is the technical bit of info I felt I was missing
somehow.
(Funny how I never considered that myself, its so obvious now)

No. 2 is something I'd read about here but forgotten!

Must try harder.


Cheers,

Gareth.

[Arny Krueger[_4_]]

"Scott Dorsey" wrote in message
...
Gareth Magennis wrote:

Say you have a control room and a live room connected with a single
multicore, down which you will have your mic feeds and will also be
sending
headphone feeds back.
I've always assumed it would be far better to have the headphone amps in
the
live room, as sending "power" down the multicore may induce crosstalk into
the mic feeds, where sending just the signal may not.

Is this actually the case? The voltage in a powered headphone feed is
presumably comparable-ish with line levels, but obviously carries
current.
Does that current make crosstalk more likely?

The increased current isn't a big deal but....

1. it's not a balanced signal. It's two unbalanced lines wrapped into the
same pair, so anything that isn't common to both channels will be
radiating
some magnetic field.

Someone needs to review circuits 101 on that one! By definition the sum of
the current in the outbound signal lines equals the return current in the
return line (shield), so the sum of the currents is zero. Since the three
wires are in close proximity, they truly sum magnetically.

In fact the voltage supplied to headphones can be the same as that in a
regular line level pair.

There's no practical difference, and it doesn't matter where the headphone
amp is, except for the resistance of the length of the line, which is again
likely to be nominal.

[Scott Dorsey]

Arny Krueger wrote:

1. it's not a balanced signal. It's two unbalanced lines wrapped into the
same pair, so anything that isn't common to both channels will be
radiating
some magnetic field.

Someone needs to review circuits 101 on that one! By definition the sum of
the current in the outbound signal lines equals the return current in the
return line (shield), so the sum of the currents is zero. Since the three
wires are in close proximity, they truly sum magnetically.

They aren't in close enough proximity, that's the problem.

The shield is the return for both of the signal lines. If the current
were perfectly distributed around the shield, there would be no electrostatic
radiation. But as long as they aren't all sharing the same physical
space, there is a loop and there will be magnetic radiation. The whole
point of the twisted pair arrangement is to minimize loop area and to
make it equal in all directions so in theory it cancels out.

in fact the voltage supplied to headphones can be the same as that in a
regular line level pair.

Yes.

There's no practical difference, and it doesn't matter where the headphone
amp is, except for the resistance of the length of the line, which is again
likely to be nominal.

It's just like any other unbalanced line. However, you'll find with a hundred
feet of multicore and a 50 ohm headphone (or a bunch of 600 ohm phones in
parallel from a headphone box) that the resistance is not minimal.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Richard Webb[_3_]]

On Sun 2011-Oct-16 09:56, Scott Dorsey writes:

Arny Krueger wrote:
1. it's not a balanced signal. It's two unbalanced lines wrapped into the
same pair, so anything that isn't common to both channels will be
radiating
some magnetic field.

Someone needs to review circuits 101 on that one! By definition the sum of
the current in the outbound signal lines equals the return current in the
return line (shield), so the sum of the currents is zero. Since the three
wires are in close proximity, they truly sum magnetically.

They aren't in close enough proximity, that's the problem.

YEp.

The shield is the return for both of the signal lines. If the
current were perfectly distributed around the shield, there would be
no electrostatic radiation. But as long as they aren't all sharing
the same physical space, there is a loop and there will be magnetic
radiation. The whole point of the twisted pair arrangement is to
minimize loop area and to make it equal in all directions so in
theory it cancels out.

YEp, but that's theory. DAy to day operation can differ a
bit though g.

snip
There's no practical difference, and it doesn't matter where the headphone
amp is, except for the resistance of the length of the line, which is again
likely to be nominal.

It's just like any other unbalanced line. However, you'll find with
a hundred feet of multicore and a 50 ohm headphone (or a bunch of
600 ohm phones in parallel from a headphone box) that the resistance
is not minimal.

Which is why I'd run my line level signals down the
multicore and the headphone amp at the far end. Just
minimizes any potential problems. After all, one session I
might only have one set of cans connected, then later on
half a dozen, etc. etc. Feeding my line level signals down
the snake and putting the variable part of the equation at
the far end improves reliability imho, and when the clock is running the customer doesn't like to have to take time out
for troubleshooting.



Regards,
Richard
--
| Remove .my.foot for email
| via Waldo's Place USA Fidonet-Internet Gateway Site
| Standard disclaimer: The views of this user are strictly his own.

[Arny Krueger[_4_]]

"Scott Dorsey" wrote in message
...
Arny Krueger wrote:

1. it's not a balanced signal. It's two unbalanced lines wrapped into
the
same pair, so anything that isn't common to both channels will be
radiating some magnetic field.

Someone needs to review circuits 101 on that one! By definition the sum
of
the current in the outbound signal lines equals the return current in the
return line (shield), so the sum of the currents is zero. Since the three
wires are in close proximity, they truly sum magnetically.

They aren't in close enough proximity, that's the problem.

They are a twisted pair of small guage wire inside a common shield. That's
about as intimate as it gets for separate conductors.

The shield is the return for both of the signal lines. If the current
were perfectly distributed around the shield, there would be no
electrostatic
radiation.

In fact every simple shielded twisted pair cable in the real world has some
electrostatic radiation and some electromagnetic radiation. Saying that a
cable is not balanced enough because there is some leakage is stretching a
point well beyond its logical breaking point. In the Tempest specs, a
simple shielded twisted pair may be inadequately shielded and the use of
conduit or duct as cable shielding may be indicated.

But as long as they aren't all sharing the same physical
space, there is a loop and there will be magnetic radiation.

So Scott, how is this significantly different from any other balanced line?
Is it not true that every balanced line composed of twisted pair has some
fiinite physical space between the conductors?

The whole
point of the twisted pair arrangement is to minimize loop area and to
make it equal in all directions so in theory it cancels out.

That's the whole point of a twisted pair, but a twisted pair lacks the
minimzed loop of a conductor or conductors within a shield, which is what we
are talking about here.

There's no practical difference, and it doesn't matter where the headphone
amp is, except for the resistance of the length of the line, which is
again
likely to be nominal.

It's just like any other unbalanced line.

No it isn't, because the load is floating. Consider a balanced intput on a
"balanced" transformer mic preamp which I will provide a reputable,
industry-standard reference shematic for: Jensen Transfomers.

Let's look at the schematic of the Jensen Transformer application note
http://www.jensen-transformers.com/as/as017.pdf titled: "JT-3k6-C in
simple one stage IC mic preamp"

In it we do not see a transformer with *any* center-tapped windings at all.
Instead we see a floating primary. It is electronically the same as a
speaker or a headphone load. Yet Jensen calls it "balanced". Are they
lying? Of course not!

However, you'll find with a hundred
feet of multicore and a 50 ohm headphone (or a bunch of 600 ohm phones in
parallel from a headphone box) that the resistance is not minimal.

Lets take a look at standard wire gauge tables - 200 feet of 24 guage wire
has about 5 ohms resistance. Since that is 10 times or more the load
impedances you mention, from an engineering perspective it is indeed minimal
and can be safely ignored.

Usually the resistance of the sheld of a piece of shielded wire such as is
used in multicores is far less than that of the signal wires, so the real
world number is more like 3 ohms. That would be about half of what, in an
engineering sense is usually considered to be minimal.

[Arny Krueger[_4_]]

"Richard Webb" wrote in
message ...

Which is why I'd run my line level signals down the
multicore and the headphone amp at the far end. Just
minimizes any potential problems. After all, one session I
might only have one set of cans connected, then later on
half a dozen, etc. etc. Feeding my line level signals down
the snake and putting the variable part of the equation at
the far end improves reliability imho, and when the clock is running the
customer doesn't like to have to take time out

Of course I generally do the same thing - put the headphone amp in the
vicinity of the headphones. For one thing, its a simple way to put the level
control near the user.

But the question at hand is whether or not it would be problematical. It
would not necessarily cause any audible problems.

[Scott Dorsey]

Arny Krueger wrote:

In fact every simple shielded twisted pair cable in the real world has some
electrostatic radiation and some electromagnetic radiation. Saying that a
cable is not balanced enough because there is some leakage is stretching a
point well beyond its logical breaking point. In the Tempest specs, a
simple shielded twisted pair may be inadequately shielded and the use of
conduit or duct as cable shielding may be indicated.

Yes. But it's not a twisted pair any more once you put two different
signals on the two conductors, references to ground. When you do this,
the radiation increases substantially because the cable is longer a
shielded twisted pair.

If the signal were mono, it would be a simple coax.

It's just like any other unbalanced line.

No it isn't, because the load is floating. Consider a balanced intput on a
"balanced" transformer mic preamp which I will provide a reputable,
industry-standard reference shematic for: Jensen Transfomers.

That has nothing to do with anything. That only eliminates ground loops,
it does nothing else.

The load is not floating. Both sideS

let's look at the schematic of the Jensen Transformer application note
http://www.jensen-transformers.com/as/as017.pdf titled: "JT-3k6-C in
simple one stage IC mic preamp"

In it we do not see a transformer with *any* center-tapped windings at all.
Instead we see a floating primary. It is electronically the same as a
speaker or a headphone load. Yet Jensen calls it "balanced". Are they
lying? Of course not!

It's the _cable_ that is balanced. You could, in fact, wire a headphone
connection up using two twisted pairs with the ground on each pair being
used as return, and it would be balanced.

But that is not what people do, they use a single pair for two channels.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Arny Krueger[_4_]]

"Scott Dorsey" wrote in message
...
Arny Krueger wrote:

In fact every simple shielded twisted pair cable in the real world has
some
electrostatic radiation and some electromagnetic radiation. Saying that a
cable is not balanced enough because there is some leakage is stretching
a
point well beyond its logical breaking point. In the Tempest specs, a
simple shielded twisted pair may be inadequately shielded and the use of
conduit or duct as cable shielding may be indicated.

Yes. But it's not a twisted pair any more once you put two different
signals on the two conductors, references to ground. When you do this,
the radiation increases substantially because the cable is longer a
shielded twisted pair.

Completely and uterlly wrong, and I've backed this one up with measurements
in the lab.

If the signal were mono, it would be a simple coax.

It's just like any other unbalanced line.

No it isn't, because the load is floating. Consider a balanced intput on
a
"balanced" transformer mic preamp which I will provide a reputable,
industry-standard reference shematic for: Jensen Transfomers.

That has nothing to do with anything. That only eliminates ground loops,
it does nothing else.

Wrong again. Because there is no other connection to the load, it is truely
floating and the send and return currents must be equal. In fact there are
often some stray capacitances to ground and things may get a little
unbalanced at high frequencies. But again, this is stretching the point.

The load is not floating. Both sideS

Your statement is incomplete at this point and therefore unintelligible.

let's look at the schematic of the Jensen Transformer application note
http://www.jensen-transformers.com/as/as017.pdf titled: "JT-3k6-C in
simple one stage IC mic preamp"

In it we do not see a transformer with *any* center-tapped windings at
all.
Instead we see a floating primary. It is electronically the same as a
speaker or a headphone load. Yet Jensen calls it "balanced". Are they
lying? Of course not!

It's the _cable_ that is balanced. You could, in fact, wire a headphone
connection up using two twisted pairs with the ground on each pair being
used as return, and it would be balanced.

You've just conceeded my point, apparently unknowingly.

But that is not what people do, they use a single pair for two channels.

And because the load is floating, and the current-carrying conductors are so
initmately arranged, the external magnetic field is minimal, just like it is
for a transfomer-coupled line level input stage.

At this point I'm not going to reply any further unless something that
changes the discussion is said, because the discussion is going in circles.

[Scott Dorsey]

Arny Krueger wrote:
"Scott Dorsey" wrote in message

Yes. But it's not a twisted pair any more once you put two different
signals on the two conductors, references to ground. When you do this,
the radiation increases substantially because the cable is longer a
shielded twisted pair.

Completely and uterlly wrong, and I've backed this one up with measurements
in the lab.

Strange, Motchenbacher seems to disagree with you.

Take the degenerate case of the mono signal.

Wrong again. Because there is no other connection to the load, it is truely
floating and the send and return currents must be equal. In fact there are
often some stray capacitances to ground and things may get a little
unbalanced at high frequencies. But again, this is stretching the point.

The load is floating, but a floating load connected to a coax has only
the electrostatic noise reduction from the coax, and whatever magnetic
noise reduction results from the proximity of the center conductor to the
shield. This is substantially less than a balanced twisted pair.

And because the load is floating, and the current-carrying conductors are so
initmately arranged, the external magnetic field is minimal, just like it is
for a transfomer-coupled line level input stage.

If this were the case, why wouldn't we just use balanced connections for
microphones? The microphone is floating, right? But when you actually
try it with a ten foot cable, what you get is hum and buzz.

at this point I'm not going to reply any further unless something that
changes the discussion is said, because the discussion is going in circles.

I recommend you check Henry Ott's book on the subject, also Motchenbacher.
Morrison's "Grounding And Shielding Techniques In Instrumentation" is also
a really nice reference with some sample measurements on balanced and
unbalanced lines.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Richard Webb wrote:

I've known people to argue for it at the design stage,
usually as Scott posits, using one pair for both channels.
I've always done it as I stated, for the reasons I stated.
IT obviously puts volume control closer to users, and
eliminates potential problems, whether there have been any
or not, I don't think I've worked anywhere that it was done
other than as Scott and I suggest, but might have been.

The way I like to do it is to have the power amp in the rack in the control
room, feeding some 18/3 or larger cable to a headphone distribution box.
The distribution box has resistive attenuators that allow three or four
different sets of phones with independent volume controls.

In the old days it was common to use the same amp for the studio monitors
and also the headphones, but these days there's no reason to do that sort
of thing.

WAs always just considered by me to be a matter of that thar good engineering practice to use the balanced lines as they
were intended instead of taking a perceived shortcut, though it's been suggested a couple of times in my presence. I
just never thought I was gaining anything, and the potential for headaches made me avoid it. Usually if I'm thinking of
feeding headphones down a multicore I've got two pairs to
work with, so it's just as easy to do it the other way g.

I've always seen people just use one pair and the TRS jack. And it's usually
fine.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[MarkK]

And because the load is floating, and the current-carrying conductors are
so
initmately arranged, the external magnetic field is minimal, just like it
is
for a transfomer-coupled line level input stage.

At this point I'm not going to reply any further unless something that
changes the discussion is said, because the discussion is going in
circles.


Hey Arnie,

I agree with you. As long as the load is floating the current down the 1
or 2 center conductors is equaled by the return current in the shield so
there will be minimal magnetic radiation from the cable. In fact I think
it is true that conductors coaxial orientation is better at magnetic
cancellation compared to twisting.

If the cable shield is connected to ground at the source, then there will
also be no electrostatic radiation.

So in practice, driving headphone either mono or stereo with L and R on the
two inner conductors down the multicore should not cause any crosstalk
problems AS LONG AS THE LOAD REMAINS ISOLATED FROM GROUND i.e. if the phone
jacks are isolated.

If however the phone jacks are all mounted in a metal chassis and tied to
ground at the load end, then there will be ground loops and all kinds of
problems.

Mark

[Richard Webb[_3_]]

On Sun 2011-Oct-16 17:05, Arny Krueger writes:

"Richard Webb"
wrote in message ...

Which is why I'd run my line level signals down the
multicore and the headphone amp at the far end. Just
minimizes any potential problems. After all, one session I
might only have one set of cans connected, then later on
half a dozen, etc. etc. Feeding my line level signals down
the snake and putting the variable part of the equation at
the far end improves reliability imho, and when the clock is running the
customer doesn't like to have to take time out

Of course I generally do the same thing - put the headphone amp in
the vicinity of the headphones. For one thing, its a simple way to
put the level control near the user.

But the question at hand is whether or not it would be
problematical. It would not necessarily cause any audible
problems.

I've known people to argue for it at the design stage,
usually as Scott posits, using one pair for both channels.
I've always done it as I stated, for the reasons I stated.
IT obviously puts volume control closer to users, and
eliminates potential problems, whether there have been any
or not, I don't think I've worked anywhere that it was done
other than as Scott and I suggest, but might have been.
WAs always just considered by me to be a matter of that thar good engineering practice to use the balanced lines as they
were intended instead of taking a perceived shortcut, though it's been suggested a couple of times in my presence. I
just never thought I was gaining anything, and the potential for headaches made me avoid it. Usually if I'm thinking of
feeding headphones down a multicore I've got two pairs to
work with, so it's just as easy to do it the other way g.


Regards,
Richard
--
| Remove .my.foot for email
| via Waldo's Place USA Fidonet-Internet Gateway Site
| Standard disclaimer: The views of this user are strictly his own.

[Richard Webb[_3_]]

On Sun 2011-Oct-16 21:33, Scott Dorsey writes:
The way I like to do it is to have the power amp in the rack in the
control room, feeding some 18/3 or larger cable to a headphone
distribution box. The distribution box has resistive attenuators
that allow three or four different sets of phones with independent
volume controls.

DOne that, regular power amp driving the mult box with
volume controls, friend of mine and I custom built one for
just that purpose. NEver did the same amp for the studio
monitors, always had a separate power amp for that one.

WAs always just considered by me to be a matter of that thar good engineering
practice to use the balanced lines as they
were intended instead of taking a perceived shortcut, though it's been
suggested a couple of times in my presence. I
just never thought I was gaining anything, and the potential for headaches made
me avoid it. Usually if I'm thinking of
feeding headphones down a multicore I've got two pairs to
work with, so it's just as easy to do it the other way g.

I've always seen people just use one pair and the TRS jack. And
it's usually fine.
YEah I know, as I said I've heard it advocated, but usually
I like to just use two lines, balanced lines, send the
regular line level sigs down those two lines to the
headphone amp, just as easy imho. Guess my statement on
that wasn't clear.

Regards,
Richard
--
| Remove .my.foot for email
| via Waldo's Place USA Fidonet-Internet Gateway Site
| Standard disclaimer: The views of this user are strictly his own.

[Arny Krueger[_4_]]

"Richard Webb" wrote in
message ...
On Sun 2011-Oct-16 17:05, Arny Krueger writes:

"Richard Webb"
wrote in message ...

Which is why I'd run my line level signals down the
multicore and the headphone amp at the far end. Just
minimizes any potential problems. After all, one session I
might only have one set of cans connected, then later on
half a dozen, etc. etc. Feeding my line level signals down
the snake and putting the variable part of the equation at
the far end improves reliability imho, and when the clock is running the
customer doesn't like to have to take time out

Of course I generally do the same thing - put the headphone amp in
the vicinity of the headphones. For one thing, its a simple way to
put the level control near the user.

But the question at hand is whether or not it would be
problematical. It would not necessarily cause any audible
problems.

I've known people to argue for it at the design stage,
usually as Scott posits, using one pair for both channels.
I've always done it as I stated, for the reasons I stated.
IT obviously puts volume control closer to users, and
eliminates potential problems, whether there have been any
or not, I don't think I've worked anywhere that it was done
other than as Scott and I suggest, but might have been.

My comments are intended to be theoretical, other than that I've done some
measurements that bear on the claims I made.

Today I drive 4 headphones at the stage end, but they are attached to Aviom
boxes that not only have their own headphone amps, but also have 16 channel
digital mixers which are driven over CAT5 from direct outs on the relevant
channels of the 02R96.

I'm millions of miles from the meat end of this question!

WAs always just considered by me to be a matter of that thar good
engineering practice to use the balanced lines as they
were intended instead of taking a perceived shortcut, though it's been
suggested a couple of times in my presence.

If you have to do analog, and I still do a ton of that too, balanced is
clearly the way to go. Almost all balanced lines today are implemented with
electronic, not transformer drive and electronic, not transformer receivers.
As Scott says, when transformers are used, only the line is balanced. The
transformer windings at both ends are not center tapped, and the winding is
just floating in space other than stray capacitance. I still have some
legacy gear with transformers, but little if any of it is actually in use.
Most of my mics have active circuitry, so we're talking electronic, not
transformer drive. Few mics with transformers have anything but a single
floating winding.

I just never thought I was gaining anything, and the potential for
headaches made me avoid it. Usually if I'm thinking of
feeding headphones down a multicore I've got two pairs to work with, so
it's just as easy to do it the other way g.

Agreed.

[Arny Krueger[_4_]]

"Scott Dorsey" wrote in message
...
Arny Krueger wrote:
"Scott Dorsey" wrote in message

Yes. But it's not a twisted pair any more once you put two different
signals on the two conductors, references to ground. When you do this,
the radiation increases substantially because the cable is longer a
shielded twisted pair.

Completely and uterlly wrong, and I've backed this one up with
measurements
in the lab.

Strange, Motchenbacher seems to disagree with you.

According to you, Scott. You are just saying that you think you're right and
dropping someone else's good name.

Take the degenerate case of the mono signal.

Doesn't matter. Again, you are providing no supporting evidence, just
reitertating that you think that you are right.

Wrong again. Because there is no other connection to the load, it is
truely
floating and the send and return currents must be equal. In fact there are
often some stray capacitances to ground and things may get a little
unbalanced at high frequencies. But again, this is stretching the point.

The load is floating, but a floating load connected to a coax has only
the electrostatic noise reduction from the coax, and whatever magnetic
noise reduction results from the proximity of the center conductor to the
shield. This is substantially less than a balanced twisted pair.

The floating load driven by coax responds to only to the differential
voltage between the conductor and the shield, just like a balanced line
receiver.

Therefore the statement that "a floating load connected to a coax has only
the electrostatic noise reduction from the coax" is false.

And because the load is floating, and the current-carrying conductors are
so
initmately arranged, the external magnetic field is minimal, just like it
is
for a transfomer-coupled line level input stage.

If this were the case, why wouldn't we just use balanced connections for
microphones?

Because common mode rejection at the receiving end can be a big help, even
when the transmission line is unbalanced.

When I was testing consumer gear for my old www.pcavtech.com web site, I
found that circuit 18 at http://www.rane.com/note110.html (Rane's classic
"Sound System Interconnection" paper) to provide better noise performance. I
was exploiting the common mode rejection of the circuitry at the receiving
end - simulating a floating load.

The microphone is floating, right? But when you actually
try it with a ten foot cable, what you get is hum and buzz.

at this point I'm not going to reply any further unless something that
changes the discussion is said, because the discussion is going in
circles.

I recommend you check Henry Ott's book on the subject, also Motchenbacher.
Morrison's "Grounding And Shielding Techniques In Instrumentation" is also
a really nice reference with some sample measurements on balanced and
unbalanced lines.

Been there, done that. I've also done considerable lab work in the area.

Scott, in a similar spirit as the one you show above, I recommend that you
review a good first year electrical circuits course.

[Arny Krueger[_4_]]

"MarkK" wrote in message
...

And because the load is floating, and the current-carrying conductors are
so
initmately arranged, the external magnetic field is minimal, just like it
is
for a transfomer-coupled line level input stage.

At this point I'm not going to reply any further unless something that
changes the discussion is said, because the discussion is going in
circles.


Hey Arnie,

I agree with you. As long as the load is floating the current down the 1
or 2 center conductors is equaled by the return current in the shield so
there will be minimal magnetic radiation from the cable. In fact I think
it is true that conductors coaxial orientation is better at magnetic
cancellation compared to twisting.

If the cable shield is connected to ground at the source, then there will
also be no electrostatic radiation.

So in practice, driving headphone either mono or stereo with L and R on
the
two inner conductors down the multicore should not cause any crosstalk
problems AS LONG AS THE LOAD REMAINS ISOLATED FROM GROUND i.e. if the
phone
jacks are isolated.

If however the phone jacks are all mounted in a metal chassis and tied to
ground at the load end, then there will be ground loops and all kinds of
problems.


Yes, there are times when a little plastic in the right places can be a big
help!

[Mike Rivers]

Just one more asshole with one more opinion, but I've never
hesitated to run headphones or line level signals (in either
direction) down a snake along with mic lines. Never had a
problem.

The theory is correct, but in practice the effect, unless
you're driving 50 sets of headphones in parallel with a 100
watt amplifier (I never tried that) will be negligible.
Without a test, how will you be able to tell the difference
between crosstalk in the snake, leakage from the earphone to
the mic, and leakage between instruments in the room?


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Scott Dorsey]

Arny, I'm glad you live in a world where all cables are perfectly symmetric
and never get curled or deformed, where the drain wires are layed out
perfectly and you can rely on the perfect symmetry of the cable structure for
nulling out noise.

Because... the rest of us don't live in this perfect world.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Arny Krueger[_4_]]

"Scott Dorsey" wrote in message
...
Arny, I'm glad you live in a world where all cables are perfectly
symmetric
and never get curled or deformed, where the drain wires are layed out
perfectly and you can rely on the perfect symmetry of the cable structure
for
nulling out noise.


Excluded middle argument. We all know that nothing is perfect, but the
better technology provides more than enough of the expected benefits, even
when a little bent out of shape.

[Richard Webb[_3_]]

On Mon 2011-Oct-17 08:53, Mike Rivers writes:
Just one more asshole with one more opinion, but I've never
hesitated to run headphones or line level signals (in either
direction) down a snake along with mic lines. Never had a
problem.

True, just never had occasion to do it when putting the amp
nearer the headphone users wasn't also a good option.
Although not driving 50 sets of phones, I"ve used the 100
watt amp to power my headphone mult box a time or two,
though usually it was a cheapo tuner/amp combo g and
eventually a Crown dc-60.

Essentially both sides of this argument are correct, it can
work, just one of those things I never did because it didn't buy me anything in the convenience or ease of initial setup
department. But then, I think Scott and I both approach
things a bit from the over engineering standpoint, at least
that's my take on Scott after participating regularly in
this ng for over a decade now g.

Another example of my propensity to over engineer ... I've
bought a bunch of this military style mast, fiberglass, 4 ft sections that attach easily, one to the other, no tools
required with the insert rings with attach points for
carabiners and guy lines. A friend of mine was recently
assisting me with a couple of antenna projects around here
and asked why I didn't use some of it instead of the heavy
well casing pipe I was using for one mast as it would be
easier to handle. I explained to him that this stuff was
designed for temporary installations in the field, and
that's what I used it for. YEs, I have more of it than I'd
probably ever need for one field station installation, but
that heavy well casing pipe would be sure to last a long
time, whereas the other stuff ... I'd rather use it as
intended, although it would probably hold up just as well in a long term installation grin.

Trouble is, these discussions almost reach the level of
religious wars sometimes on this group g. Doesn't help
the op much, unless he knows going in that he'll probably
get the conservative answer from folks such as Scott and
myself, and another perfectly valid answer from some other
folks.


Regards,
Richard
--
| Remove .my.foot for email
| via Waldo's Place USA Fidonet-Internet Gateway Site
| Standard disclaimer: The views of this user are strictly his own.

[Gareth Magennis]

"Richard Webb" wrote in
message ...
On Mon 2011-Oct-17 08:53, Mike Rivers writes:
Just one more asshole with one more opinion, but I've never
hesitated to run headphones or line level signals (in either
direction) down a snake along with mic lines. Never had a
problem.

True, just never had occasion to do it when putting the amp
nearer the headphone users wasn't also a good option.
Although not driving 50 sets of phones, I"ve used the 100
watt amp to power my headphone mult box a time or two,
though usually it was a cheapo tuner/amp combo g and
eventually a Crown dc-60.

Essentially both sides of this argument are correct, it can
work, just one of those things I never did because it didn't buy me
anything in the convenience or ease of initial setup
department. But then, I think Scott and I both approach
things a bit from the over engineering standpoint, at least
that's my take on Scott after participating regularly in
this ng for over a decade now g.

Another example of my propensity to over engineer ... I've
bought a bunch of this military style mast, fiberglass, 4 ft sections that
attach easily, one to the other, no tools
required with the insert rings with attach points for
carabiners and guy lines. A friend of mine was recently
assisting me with a couple of antenna projects around here
and asked why I didn't use some of it instead of the heavy
well casing pipe I was using for one mast as it would be
easier to handle. I explained to him that this stuff was
designed for temporary installations in the field, and
that's what I used it for. YEs, I have more of it than I'd
probably ever need for one field station installation, but
that heavy well casing pipe would be sure to last a long
time, whereas the other stuff ... I'd rather use it as
intended, although it would probably hold up just as well in a long term
installation grin.

Trouble is, these discussions almost reach the level of
religious wars sometimes on this group g. Doesn't help
the op much, unless he knows going in that he'll probably
get the conservative answer from folks such as Scott and
myself, and another perfectly valid answer from some other
folks.


Regards,
Richard


I dunno, as the OP, I've learnt a few more titbits of information, which was
the reason for the post.
If I am to advise the client on the best way to commision and use the wiring
I have installed for him, I really ought to know what I am talking about,
not working on a "hunch".

My prior assumption was that best practice is to site the amp in the live
room, and that not doing this is not really going to generate very many
noticable problems unless we start getting into extremes. The thread here
has pretty much confirmed this to be the case, so personally I'm happy as
Larry, whoever he happens to be.


Thanks to all.

Gareth.

[Poster]

I do headphones over multicore on a daily basis, never a problem, despite
the theory.

[Richard Webb[_3_]]

On Tue 2011-Oct-18 05:14, Gareth Magennis writes:
Essentially both sides of this argument are correct, it can
work, just one of those things I never did because it didn't buy me
anything in the convenience or ease of initial setup
department. But then, I think Scott and I both approach
things a bit from the over engineering standpoint, at least
that's my take on Scott after participating regularly in
this ng for over a decade now g.
big snip
Trouble is, these discussions almost reach the level of
religious wars sometimes on this group g. Doesn't help
the op much, unless he knows going in that he'll probably
get the conservative answer from folks such as Scott and
myself, and another perfectly valid answer from some other
folks.

I dunno, as the OP, I've learnt a few more titbits of information,
which was the reason for the post.
If I am to advise the client on the best way to commision and use
the wiring I have installed for him, I really ought to know what I
am talking about, not working on a "hunch".

INdeed, and "best practice" is usually the conservative
approach, with good reason, which is what you got from MR.
Dorsey and myself. We'll neither one argue that it won't
work, but we'll argue best practice, big difference, and a
lot of folks lose sight of that.

My prior assumption was that best practice is to site the amp in the
live room, and that not doing this is not really going to generate
very many noticable problems unless we start getting into extremes.
The thread here has pretty much confirmed this to be the case, so
personally I'm happy as Larry, whoever he happens to be.

INdeed, which is why "best practice" is usually stated as
such. IF you stay within parameters defined by it usually
the extremes won't reach out and bite you. FOlks will
remember a long running discussion about a year ago in this
group re transformer isolated splits on mic lines vs other
approaches to feed multiple mixers.
Cutting corners may work for one person's application, but
if he stays withn what's considered best practice he's
assured that everything functions as it should. Glad the
discussion was helpful to you.



Regards,
Richard
--
| Remove .my.foot for email
| via Waldo's Place USA Fidonet-Internet Gateway Site
| Standard disclaimer: The views of this user are strictly his own.

[Tobiah[_4_]]

YEp, but that's theory. DAy to day operation can differ a
bit thoughg.

I heard that idea expressed well recently - I hope is wasn't he

In theory, practice and theory are the same. In practice, they are not.

[Trevor]

"Don Pearce" wrote in message
...
On Mon, 24 Oct 2011 11:03:14 -0700, Tobiah
In theory, practice and theory are the same. In practice, they are not.

If practice and theory are not the same, your theory isn't good
enough.

Or your practice!

I used to believe that microwave system design was a black
art, I now know it is pure science.

That simply means you were ill informed, now you know better.

Trevor.

[Don Pearce[_3_]]

On Tue, 25 Oct 2011 07:49:10 +1100, "Trevor" wrote:


"Don Pearce" wrote in message
...
On Mon, 24 Oct 2011 11:03:14 -0700, Tobiah
In theory, practice and theory are the same. In practice, they are not.

If practice and theory are not the same, your theory isn't good
enough.

Or your practice!

I used to believe that microwave system design was a black
art, I now know it is pure science.

That simply means you were ill informed, now you know better.


Exactly.

d

[Meindert Sprang]

"Don Pearce" wrote in message
...
If practice and theory are not the same, your theory isn't good
enough. I used to believe that microwave system design was a black
art, I now know it is pure science.

No it's not. It's pure plumbing ;-)

Meindert

[hank alrich]

Meindert Sprang wrote:

"Don Pearce" wrote in message
...
If practice and theory are not the same, your theory isn't good
enough. I used to believe that microwave system design was a black
art, I now know it is pure science.

No it's not. It's pure plumbing ;-)

Meindert

Now you're talking black science.

--
shut up and play your guitar * http://hankalrich.com/
http://www.youtube.com/walkinaymusic
http://www.sonicbids.com/HankandShaidri

[Scott Dorsey]

Don Pearce wrote:
On Tue, 25 Oct 2011 07:49:10 +1100, "Trevor" wrote:
"Don Pearce" wrote in message
...
On Mon, 24 Oct 2011 11:03:14 -0700, Tobiah
In theory, practice and theory are the same. In practice, they are not.

If practice and theory are not the same, your theory isn't good
enough.

Or your practice!

I used to believe that microwave system design was a black
art, I now know it is pure science.

That simply means you were ill informed, now you know better.

Exactly.

However, knowing that there is a scientific rationale behind it does not
tell you precisely where to hit the waveguide with a hammer to eliminate
the spur.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Don Pearce[_3_]]

On 25 Oct 2011 11:14:55 -0400, (Scott Dorsey) wrote:

Don Pearce wrote:
On Tue, 25 Oct 2011 07:49:10 +1100, "Trevor" wrote:
"Don Pearce" wrote in message
...
On Mon, 24 Oct 2011 11:03:14 -0700, Tobiah
In theory, practice and theory are the same. In practice, they are not.

If practice and theory are not the same, your theory isn't good
enough.

Or your practice!

I used to believe that microwave system design was a black
art, I now know it is pure science.

That simply means you were ill informed, now you know better.

Exactly.

However, knowing that there is a scientific rationale behind it does not
tell you precisely where to hit the waveguide with a hammer to eliminate
the spur.

I recently designed some waveguide filters - very steep sided bandpass
filters at 30GHz. They are now in the field and working and there was
just a single iteration of the design. Sufficient theory and a great
deal of work before starting the design meant that I didn't have to
hit them with a hammer.

d

[Don Pearce[_3_]]

On Tue, 25 Oct 2011 10:48:00 +0200, "Meindert Sprang"
wrote:

"Don Pearce" wrote in message
...
If practice and theory are not the same, your theory isn't good
enough. I used to believe that microwave system design was a black
art, I now know it is pure science.

No it's not. It's pure plumbing ;-)

Do you know what plumbers earn? Ha!

d