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Shielding approaches for 4pin XLR headphone cable
Shielding approaches for 4pin XLR headphone cable
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Old 26th March 2019, 07:44 PM   #21
Bonsai is online now Bonsai  Europe
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Quote:
Originally Posted by DF96 View Post
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.


I think I got that wrong.
How much cross talk you are going to pick-up in a 1 or 2 metre headphone cable. Is it audible? Does it matter?
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Old 27th March 2019, 10:43 AM   #22
DF96 is offline DF96  England
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If you wired it wrongly then at higher audio frequencies you might get enough crosstalk to be noticeable. Anyway, as always, numbers are our friend.

Let us first estimate the inductance of a 2m cable. A closely spaced pair will typically have an RF characteristic impedance in the range 50-100 ohms. That means an inductance of around 0.3uH/m, so 0.6uH in all. At 20kHz this will have an impedance of 0.075R. Comparing this with a ruling impedance of, say, 30 ohms it is at the level of -52dB. The two sets of wires will not be 100% coupled, but nevertheless we can predict crosstalk around the -60dB level. OK, probably not an issue. However, correctly wiring the star quad cable will drop this further.
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Old 30th March 2019, 01:52 AM   #23
Rick PA Stadel is offline Rick PA Stadel  United States
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O.K., but its only the load that is ~32 ohms, right? I would think most any headphone output's impedance would be quite a bit lower, reducing received EMI at least.

The only interference problem I've ever had with headphones was an occasional output that needed an RF choke -- on a busy street, a passing emergency vehicle radio would sneak in once in a while.

IMHO you may be over-thinking this, but best of luck anyway,
Rick
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Old 30th March 2019, 11:35 AM   #24
DF96 is offline DF96  England
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Low output impedance helps magnetic crosstalk; it only inhibits capacitive crosstalk.
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Old 31st March 2019, 01:09 PM   #25
Bonsai is online now Bonsai  Europe
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Quote:
Originally Posted by DF96 View Post
If you wired it wrongly then at higher audio frequencies you might get enough crosstalk to be noticeable. Anyway, as always, numbers are our friend.

Let us first estimate the inductance of a 2m cable. A closely spaced pair will typically have an RF characteristic impedance in the range 50-100 ohms. That means an inductance of around 0.3uH/m, so 0.6uH in all. At 20kHz this will have an impedance of 0.075R. Comparing this with a ruling impedance of, say, 30 ohms it is at the level of -52dB. The two sets of wires will not be 100% coupled, but nevertheless we can predict crosstalk around the -60dB level. OK, probably not an issue. However, correctly wiring the star quad cable will drop this further.

I got a similar number so ya see - not a problem!
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Old 31st March 2019, 01:19 PM   #26
DF96 is offline DF96  England
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Some people worry about resistor distortion at the -120dB level! Not me, I hasten to add.
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