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Is twin core better for a 5m Headphone extension cable?



 
 
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  #11  
Old March 31st 15, 09:40 AM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
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Posts: 4,192
Default Is twin core better for a 5m Headphone extension cable?

In article , Johny B Good
wrote:
However, using a common return wire will introduce such crosstalk issues
on wire thin enough to provide a minimally acceptable flexibility.
Indeed with the spiral wound copper tape over nylon thread conductor
construction as used in telephone handset cords[1], the problem would
become quite significant if a common return wire was used (much higher
resistance per metre compared to a traditional stranded conductor using
the same weight of copper per mile - half an ohm per metre or so
compared to 0.1 ohm or less) in a 3 to 5 metre headphone cord (coiled or
straight).


FWIW some years ago I experimented with delierately adding a crossfeed
resistor for stereo to introduce crosstalk. My impression was that it
actually could give a slightly better sound. Both for speaker systems and
headphones. Although in practice crosstalk of less than 20dB about tended
to be un-noticable. I guess this depends on the listener, speakers, etc,
though. So YMMV.

Crosstalk got a bad name in the early HiFi days because when you examined
it, the crosstalk tended to be largely distortion, not simply leaked
signal. So you tend to want a low crosstalk in something like an amplifier
or cartridge because of the risk it will be distortion. If its clean, 20dB
is likely to be fine in my experience.

For 30 Ohm phones that translates to about 3 Ohms of common mode lead
resistance. But how much extra might be due to other forms of coupling, I
don't know. Depends on the cable geometry.

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

  #12  
Old March 31st 15, 01:26 PM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
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Posts: 2,158
Default Is twin core better for a 5m Headphone extension cable?

On Tue, 31 Mar 2015 09:40:58 +0100, Jim Lesurf
wrote:

FWIW some years ago I experimented with delierately adding a crossfeed
resistor for stereo to introduce crosstalk. My impression was that it
actually could give a slightly better sound. Both for speaker systems and
headphones. Although in practice crosstalk of less than 20dB about tended
to be un-noticable. I guess this depends on the listener, speakers, etc,
though. So YMMV.


I recall a magazine article (WW probably though I'm not sure), about a
system for introducing crosstalk in headphones, but with a slight
delay, which was supposed to make the sound more spacious, rather than
seeming to come from inside your own head.

I built one, but wasn't convinced I could hear any difference. I
wasn't completely surprised by this as it only used passive
components, so the delay probably wouldn't have amounted to much more
than a bit of phase shift. It seems the sort of thing which in
principle should work if done properly, i.e. with actual delay rather
than a few passive components.

Crosstalk got a bad name in the early HiFi days because when you examined
it, the crosstalk tended to be largely distortion, not simply leaked
signal. So you tend to want a low crosstalk in something like an amplifier
or cartridge because of the risk it will be distortion. If its clean, 20dB
is likely to be fine in my experience.


That tallies with my experience with cheap gramophone pickups. It
would sometimes be possible to transform poor quality stereo into
quite pleasant sounding mono by shorting the left and right outputs
together. Perhaps your resistive crossfeed arrangement was simply
reducing the amount of distortion?

Rod.
  #13  
Old March 31st 15, 01:50 PM posted to uk.tech.digital-tv
Ian Jackson[_2_]
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Posts: 2,968
Default Is twin core better for a 5m Headphone extension cable?

In message , Jim Lesurf
writes
In article , Johny B Good
wrote:
However, using a common return wire will introduce such crosstalk issues
on wire thin enough to provide a minimally acceptable flexibility.
Indeed with the spiral wound copper tape over nylon thread conductor
construction as used in telephone handset cords[1], the problem would
become quite significant if a common return wire was used (much higher
resistance per metre compared to a traditional stranded conductor using
the same weight of copper per mile - half an ohm per metre or so
compared to 0.1 ohm or less) in a 3 to 5 metre headphone cord (coiled or
straight).


FWIW some years ago I experimented with delierately adding a crossfeed
resistor for stereo to introduce crosstalk. My impression was that it
actually could give a slightly better sound. Both for speaker systems and
headphones. Although in practice crosstalk of less than 20dB about tended
to be un-noticable. I guess this depends on the listener, speakers, etc,
though. So YMMV.

Crosstalk got a bad name in the early HiFi days because when you examined
it, the crosstalk tended to be largely distortion, not simply leaked
signal. So you tend to want a low crosstalk in something like an amplifier
or cartridge because of the risk it will be distortion. If its clean, 20dB
is likely to be fine in my experience.

For 30 Ohm phones that translates to about 3 Ohms of common mode lead
resistance. But how much extra might be due to other forms of coupling, I
don't know. Depends on the cable geometry.

Maybe we need to consider the difference between 'stereophonic' and
'binaural' audio.

In the former (with speakers), both ears hear both speakers. Even in an
anechoic situation, it is unlikely that the sound reaching one ear will
be anything like 20db down on the other. If so, 20db of cable crosstalk
is likely to go unnoticed.

In the latter (with headphones), the left ear only hears what is fed to
the left speaker, and the right ear only hears what is fed to the right
speaker. I presume the effect is to enhance the image separation. Here,
20dB of cable crosstalk may indeed be noticeable, and its effect may be
to make the headphone audio sound more like speaker stereo - and
therefore possibly more 'natural'.

[I believe that when the intention is to deliberately produce binaural
audio, the microphones are also usually arranged differently in order to
keep the two channels more separate than with stereo.]


--
Ian
  #14  
Old March 31st 15, 02:14 PM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
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Posts: 4,192
Default Is twin core better for a 5m Headphone extension cable?

In article , Roderick Stewart
wrote:
On Tue, 31 Mar 2015 09:40:58 +0100, Jim Lesurf
wrote:


FWIW some years ago I experimented with delierately adding a crossfeed
resistor for stereo to introduce crosstalk. [snip]


I recall a magazine article (WW probably though I'm not sure), about a
system for introducing crosstalk in headphones, but with a slight delay,
which was supposed to make the sound more spacious, rather than seeming
to come from inside your own head.


Yes, there have been a few suggested such methods. But...

I built one, but wasn't convinced I could hear any difference.


Like yourself I wasn't sure they did much until the actual level of
crosstalk reached something more like 6dB.

FWIW I was only trying using a resistive crossover. (I actually put this
into the output of a Quad 34.) And mainly for use with a pair of ESL
speaker. Which have a much higher 'direct to ambient' ratio than
box-and-cone speakers because of their directional patterns. The effect
seemed to me to be twofold. It seemed to help the low bass, and slightly
reduced the tendency for many commercial CDs to have too wide a seperation.
e.g. The absurdly wide pianos whose keyboard reached from one speaker to
the other. Or orchestral recording with a 'hole in the middle'. However the
effect were slight.


That tallies with my experience with cheap gramophone pickups. It would
sometimes be possible to transform poor quality stereo into quite
pleasant sounding mono by shorting the left and right outputs together.


Yes. FWIW its quite common for stereo cartridges to give higher distortion
for vertical (difference). You can see this in some of the magazine
measurement that bother to do V and H tests. Alas not all do. And by
summing you also tend to drop the LF noise background which can affect what
you percieve.

Perhaps your resistive crossfeed arrangement was simply reducing the
amount of distortion?


Probably not in most cases as the amps and speakers are low distortion, and
I was mainly listening to CDs at the time. And a 20dB crossfeed won't do a
lot to reduce pure difference. I still get 'spaced out' effects behind my
head from some Jimi Hendrix recordings. 8-]

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

  #15  
Old March 31st 15, 02:17 PM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
external usenet poster
 
Posts: 4,192
Default Is twin core better for a 5m Headphone extension cable?

In article , Ian Jackson
wrote:

In the latter (with headphones), the left ear only hears what is fed to
the left speaker, and the right ear only hears what is fed to the right
speaker.


This isn't quite true. Keith Howard has in recent years been doing
measurements showing how much audio travels from one earpiece to the other
via the harness that holds them against the head. It may be quite a
significant contribution to the sound of some headphones. But depends also
on your head.

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

  #16  
Old March 31st 15, 02:35 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
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Posts: 853
Default Is twin core better for a 5m Headphone extension cable?

On Tue, 31 Mar 2015 09:40:58 +0100, Jim Lesurf
wrote:

In article , Johny B Good
wrote:
However, using a common return wire will introduce such crosstalk issues
on wire thin enough to provide a minimally acceptable flexibility.
Indeed with the spiral wound copper tape over nylon thread conductor
construction as used in telephone handset cords[1], the problem would
become quite significant if a common return wire was used (much higher
resistance per metre compared to a traditional stranded conductor using
the same weight of copper per mile - half an ohm per metre or so
compared to 0.1 ohm or less) in a 3 to 5 metre headphone cord (coiled or
straight).


FWIW some years ago I experimented with delierately adding a crossfeed
resistor for stereo to introduce crosstalk. My impression was that it
actually could give a slightly better sound. Both for speaker systems and
headphones. Although in practice crosstalk of less than about 20dB tended
to be un-noticable. I guess this depends on the listener, speakers, etc,
though. So YMMV.


The effect of crosstalk due to volt drop in a common return wire will
be anti-phase and only apply to headphone cables. Speaker cables are
never run alongside of each other in practice and never use a common
return.

Although commodity earphones as used with 'walkman' styled digital
portable players just might use twin cored co-ax where the outer
shield is used as a common return and each wire of the pair used as a
signal wire to feed the speaker transducers (the extra joint required
can be hiidden inside one of the earpieces, this would be a rather
unusually 'expensive' way to reduce material costs.

Even cheap commodity earbud headphones will use seperate thin and
flexible co-axial cables (twin co-ax) which split off at a lump of
plastic either slidable or moulded onto the twin co-ax so the issue of
common ground return impedance becoming a factor in cross-talk leakage
simply doesn't arise.

Crosstalk got a bad name in the early HiFi days because when you examined
it, the crosstalk tended to be largely distortion, not simply leaked
signal. So you tend to want a low crosstalk in something like an amplifier
or cartridge because of the risk it will be distortion. If its clean, 20dB
is likely to be fine in my experience.

For 30 Ohm phones that translates to about 3 Ohms of common mode lead
resistance. But how much extra might be due to other forms of coupling, I
don't know. Depends on the cable geometry.


Assuming a balanced circuit, the best (theoretically perfect) way to
lay two pairs together to totally eliminate crosstalk is to lay the
four conductors up in a star quad layout (each pair uses the
diagonally opposite wire as seen in cross section).

Unbalancing the circuit will compromise immunity to external
interference fields (in this case electric fields only - the seperate
ground return wires will cancel magnetic coupling when the loads don't
have an independent ground connection of their own). However, this
question of susceptability to electric fleld interference in either
direction is not an issue with sub 30 metre cables.

What is left is the fact that the single ended amplifier outputs rely
on a common ground return which unbalances the 'star quad transmission
line' introducing some level of crosstalk between the pairs. The
inductive coupling nulls out between the pairs due to the physical
layout and remains unaffected by this unbalance. This leaves us just
the issue of capacitive coupling.

Capactively induced crosstalk increases with frequency (naturally
favouring the higher frequencies - harmonics natural to the music or
distortion products alike). Googling to get some sense of typical
inter-wire capacitance values leads me to assume a worst case value of
256pF per metre.

Using this 'worst case' figure for a 100 metre headphone cable
produces a Z value of 310.85 ohms, around ten times the impedance of a
32 ohm transducer which approximates to 20dB crosstalk at 20KHz.

Assuming we stick with the cheap 32 ohm transducers, a very long
headphone lead of 10 metres will suffer crosstalk at 20KHz somewhere
close to 40db. At a more realistic 5 metres this will be circa 45dB
and if we consider HiFi quality 8 ohm transducers the attenuation
figure will increase by another 12dB to around the 57dB mark.

The manufacturers of HiFi quality headphones will be well aware of
the crosstalk issues in the durable and flexible cables needed to make
the use of their product as comfortable and practical as possible so
will avoid unnecessary screening both around and between the two
circuit pairs to maintain flexibility and lightness. A simple star
quad conductor layout will serve this purpose more than adequately,
even for the more outlandish headphone cable cord lengths of 10 to 15
metres.

If you can get hold of some actual headphone cable data on conductor
capacitance per metre values, you can do your own calculations (but
don't forget the screening effect of the ground return wires that
partially screen each signal wire from each other - I deliberately
neglected this in my 'worst case scenario' :-).
--
J B Good
  #17  
Old March 31st 15, 02:55 PM posted to uk.tech.digital-tv
Ian Jackson[_2_]
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Posts: 2,968
Default Is twin core better for a 5m Headphone extension cable?

In message , Jim Lesurf
writes
In article , Ian Jackson
wrote:

In the latter (with headphones), the left ear only hears what is fed to
the left speaker, and the right ear only hears what is fed to the right
speaker.


This isn't quite true. Keith Howard has in recent years been doing
measurements showing how much audio travels from one earpiece to the other
via the harness that holds them against the head. It may be quite a
significant contribution to the sound of some headphones. But depends also
on your head.

Maybe. I appreciate that with 'proper' headphones there could be some
mechanical transfer of sound from one side to the other. However, I
would guess that it's usually well below 20dB down. You certainly
wouldn't get it with a pair of 'plug-in-the-lug' earpieces.


--
Ian
  #18  
Old March 31st 15, 08:54 PM posted to uk.tech.digital-tv
Vir Campestris
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Posts: 404
Default Is twin core better for a 5m Headphone extension cable?

On 30/03/2015 21:56, Johny B Good wrote:
There's no need to 'screen' the seperate pairs so any headphone
manufacturer of quality will use the high resistance, ultra-flexible
conductor construction laid up in a star quad configuration to null
out inductive crosstalk with the totally insignificant residual
electric field coupling due to the use of unipolar drivers using a
common return merely being attenuated by the presence of the common
return wires adjacent to and either side of each 'signal' wire.
Furthermore, there's no reason to enclose the conductors with a
screening layer which would only compromise the cable's flexibility
for no percievable benefit.


Mine have shotgun looks-like-twin-screened cable. The two separate a
foot or so before the headphone in a little sleeve, and one goes to each
side.

I'm not prepared to wreck 3m of nice cable just to find out if the round
insulation contains coax or not.

Andy
  #19  
Old April 1st 15, 09:21 AM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
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Posts: 4,192
Default Is twin core better for a 5m Headphone extension cable?

In article , Vir
Campestris wrote:
On 30/03/2015 21:56, Johny B Good wrote:
There's no need to 'screen' the seperate pairs so any headphone
manufacturer of quality will use the high resistance, ultra-flexible
conductor construction laid up in a star quad configuration to null
out inductive crosstalk with the totally insignificant residual
electric field coupling due to the use of unipolar drivers using a
common return merely being attenuated by the presence of the common
return wires adjacent to and either side of each 'signal' wire.
Furthermore, there's no reason to enclose the conductors with a
screening layer which would only compromise the cable's flexibility
for no percievable benefit.


Mine have shotgun looks-like-twin-screened cable. The two separate a
foot or so before the headphone in a little sleeve, and one goes to each
side.


I'm not prepared to wreck 3m of nice cable just to find out if the round
insulation contains coax or not.


Don't worry about it. Even co-ax or quad tend not to work perfectly when
the cables are shoved up against one another, screen thicknesses are small,
etc. So it comes down to how well the cables were made, not just the choice
of cable topology.

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

  #20  
Old April 1st 15, 08:03 PM posted to uk.tech.digital-tv
Johny B Good[_2_]
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Posts: 853
Default Is twin core better for a 5m Headphone extension cable?

On Tue, 31 Mar 2015 20:54:29 +0100, Vir Campestris
wrote:

On 30/03/2015 21:56, Johny B Good wrote:
There's no need to 'screen' the seperate pairs so any headphone
manufacturer of quality will use the high resistance, ultra-flexible
conductor construction laid up in a star quad configuration to null
out inductive crosstalk with the totally insignificant residual
electric field coupling due to the use of unipolar drivers using a
common return merely being attenuated by the presence of the common
return wires adjacent to and either side of each 'signal' wire.
Furthermore, there's no reason to enclose the conductors with a
screening layer which would only compromise the cable's flexibility
for no percievable benefit.


Mine have shotgun looks-like-twin-screened cable. The two separate a
foot or so before the headphone in a little sleeve, and one goes to each
side.

I'm not prepared to wreck 3m of nice cable just to find out if the round
insulation contains coax or not.


I keep seeing references to "shotgun cable" which, until just now, I
had no fekin' idea what it was. I do now (and more fool the stupid
**** who thought the word shotgun would immediately conjure up the
image of a _double_ barrelled type of shotgun).

It seems I now have a handy readymade descriptor for the type of
'twin co-ax' and related types of cable to use when describing such
earpiece cords.

Getting back to your lack of enthusiasm to destroy a 3 metre piece of
nice cable, I wouldn't bother. It's quite obvious that it's simply a
shotgun cable made up from two thin and highly flexible co-axial
cables. There's no common ground return to generate anti-phase
crosstalk and the co-axial cables provide shielding (magnetic and
electric) so no crosstalk of any kind to worry about.

The use of co-axial construction is totally unnecessary even with
ridiculously long closed back headphone cords. An unscreened star quad
cord using highly flexible conductors will serve equally well. The
star quad layout nulls out inductive coupling and the residual
capacitive coupling, even on a 30 metre headphone cord, are nowhere
near enough, even with 32 ohm drivers to be an issue.
--
J B Good
 




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