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Shielding approaches for 4pin XLR headphone cable
Shielding approaches for 4pin XLR headphone cable
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Old 23rd March 2019, 08:32 PM   #11
Galu is offline Galu  Scotland
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Quote:
Originally Posted by itsikhefez View Post
When using for conductors in the headphone, we will have 2 channels, so not utilizing the star quad advantage.
I understand that, so why are we agonising over the correct way to use star quad cable in your application?

The short length of a headphone cable makes it pretty immune to RFI pick up anyway, so any decent 4 core screened cable should suffice.
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Old 23rd March 2019, 08:41 PM   #12
itsikhefez is offline itsikhefez  United States
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Shielding approaches for 4pin XLR headphone cable
Yes, I appreciate your input here.
In terms of the star quad, even though we aren’t using it as intended, I assumed that it would be preferable (even if only in theory) to use a twisted pair per channel.
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Old 23rd March 2019, 08:46 PM   #13
scottjoplin is offline scottjoplin  Wales
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Do you have a problem with RFI? I tried extending my headphone lead and had problems, using two coaxial cables cured it
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Old 23rd March 2019, 09:37 PM   #14
itsikhefez is offline itsikhefez  United States
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Shielding approaches for 4pin XLR headphone cable
Quote:
Originally Posted by scottjoplin View Post
Do you have a problem with RFI? I tried extending my headphone lead and had problems, using two coaxial cables cured it
No issues with RFI yet.
So similar to option 3 in the original post? Which cable did you use?
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Old 23rd March 2019, 10:15 PM   #15
scottjoplin is offline scottjoplin  Wales
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Yes. It was some old Shark interconnect coax
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Old 25th March 2019, 11:05 AM   #16
DF96 is offline DF96  England
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Quote:
Originally Posted by itsikhefez
In terms of the star quad, even though we aren’t using it as intended, I assumed that it would be preferable (even if only in theory) to use a twisted pair per channel.
Yes, twisted pair per channel is best. Star quad does not have a pair of twisted pairs; it has a twisted quad, so however you wire it you may get interchannel crosstalk. It is the wrong cable for the job.
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Old 25th March 2019, 04:32 PM   #17
Bonsai is offline Bonsai  Europe
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If what you are doing is driving a pair of headphones - typically 32 Ohms these days - I really don't think you need to fuss about this. As long as the cables are in close proximity and the total area bounded by the signal and return is small (which it will be) you will be radiating insignificant EM energy and neither will you be picking anything up. Keep in mind your source impedance will be low, the headphone impedance is low, so cross talk is a non-issue in this application.
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Old 25th March 2019, 07:27 PM   #18
scottjoplin is offline scottjoplin  Wales
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Re crosstalk, from here Star quad cable - Wikipedia

Star-quad cable can be used for two circuits, such as four-wire telephony and other telecommunications applications, but it will not provide magnetic immunity in this application. In this configuration each pair uses two non-adjacent conductors. Because the conductors are always the same distance from each other, crosstalk is reduced relative to cables with two separate twisted pairs. Each conductor of one pair sees an equal capacitance to both wires in the other pair. This cancels the capacitive crosstalk between the two pairs. The geometry also cancels the magnetic interference between the two pairs.
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Old 26th March 2019, 10:33 AM   #19
DF96 is offline DF96  England
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Quote:
Originally Posted by Bonsai
Keep in mind your source impedance will be low, the headphone impedance is low, so cross talk is a non-issue in this application.
True for capacitive crosstalk. Irrelevant for magnetic crosstalk.

To get low magnetic crosstalk you have to use the conductors in the right way. Use them wrongly and you get significant crosstalk - worse than a pair of twisted pairs.

Quote:
Originally Posted by DF96
it has a twisted quad, so however you wire it you may get interchannel crosstalk. It is the wrong cable for the job.
I think I got that wrong.
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Old 26th March 2019, 05:16 PM   #20
itsikhefez is offline itsikhefez  United States
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Shielding approaches for 4pin XLR headphone cable
Quote:
Originally Posted by DF96 View Post
Yes, twisted pair per channel is best. Star quad does not have a pair of twisted pairs; it has a twisted quad, ...
Yes, I had the wrong assumption that these were 2 pairs and not 4 conductors twisted together

Quote:
Originally Posted by scottjoplin View Post
Re crosstalk, from here Star quad cable - Wikipedia

Star-quad cable can be used for two circuits, such as four-wire telephony and other telecommunications applications, but it will not provide magnetic immunity in this application. In this configuration each pair uses two non-adjacent conductors. Because the conductors are always the same distance from each other, crosstalk is reduced relative to cables with two separate twisted pairs. Each conductor of one pair sees an equal capacitance to both wires in the other pair. This cancels the capacitive crosstalk between the two pairs. The geometry also cancels the magnetic interference between the two pairs.
This clarifies things. This means that if using star quad for 2 channels, we should actually use 2 blues and 2 whites (for Canare cable, for example), since those are non-adjacent to each other. This, as opposed to my wrong statement earlier to use blue/white for each channel.

Before this post I went on an extremely frustrating search to find cable that has 2 individual twisted pairs that would be suitable for headphone use.
I ordered a few samples of:
West Penn Wire D25430
Canare MR202-2AT
Belden 827232

I will have to decide between one of these and the starquad since I dont want to build multiple cables
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