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Author Topic: Are all "microphone" cables generally twisted pair?  (Read 6581 times)

Dan Brandesky

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Are all "microphone" cables generally twisted pair?
« on: April 17, 2014, 11:55:26 am »

Hi all, I have an application at work that's not quite live sound, but could potentially use microphone cable. Essentially, it's frequency-shift key communications (FSK). I need a shielded twisted pair cable that won't break the bank, and it occurred to me that microphone cable may work. However, I can't find anything online that tells me whether a typically rubber jacket microphone cable is twisted pair or not. I could also use a plenum cable in this case (the cable isn't going anywhere once it's set up), so if there's an even cheaper alternative in that realm I'd appreciate suggestions. As long as the cable has at least 2 conductors and is shielded, I'm happy!

Thanks,
Dan
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Mac Kerr

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Re: Are all "microphone" cables generally twisted pair?
« Reply #1 on: April 17, 2014, 01:47:36 pm »

Hi all, I have an application at work that's not quite live sound, but could potentially use microphone cable. Essentially, it's frequency-shift key communications (FSK). I need a shielded twisted pair cable that won't break the bank, and it occurred to me that microphone cable may work. However, I can't find anything online that tells me whether a typically rubber jacket microphone cable is twisted pair or not. I could also use a plenum cable in this case (the cable isn't going anywhere once it's set up), so if there's an even cheaper alternative in that realm I'd appreciate suggestions. As long as the cable has at least 2 conductors and is shielded, I'm happy!

Thanks,
Dan

All mic cable is shielded twisted pair, however shielded CAT5 will be cheaper if ruggedness isn't a factor. And FSK would probably be fine with unshielded CAT5.

Mac
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Dan Brandesky

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Re: Are all "microphone" cables generally twisted pair?
« Reply #2 on: April 17, 2014, 04:27:25 pm »

All mic cable is shielded twisted pair, however shielded CAT5 will be cheaper if ruggedness isn't a factor. And FSK would probably be fine with unshielded CAT5.

Mac

Thanks for the confirmation! I tried CAT5 already but since it's not shielded I get too much cross talk between the pairs. The "real" cable people use for this has two individually shielded twisted pairs in one jacket, but it's also about 5x the cost of microphone cable, so even if I have to use twice as much cable, it will still be cheaper.
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Jonathan Kok

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Re: Are all "microphone" cables generally twisted pair?
« Reply #3 on: April 17, 2014, 05:14:49 pm »

Thanks for the confirmation! I tried CAT5 already but since it's not shielded I get too much cross talk between the pairs. The "real" cable people use for this has two individually shielded twisted pairs in one jacket, but it's also about 5x the cost of microphone cable, so even if I have to use twice as much cable, it will still be cheaper.
There's nothing stopping you from getting two pair shielded. Also nothing stopping you from going generic. Talk to a large cable manufacturer; they've probably got something that will do the trick. A quick check of Anixter's site lists 73 2-pair shielded cable (mylar shield; 40 with braided shield), of varying gauge.
« Last Edit: April 17, 2014, 05:27:17 pm by Jonathan Kok »
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Mac Kerr

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Re: Are all "microphone" cables generally twisted pair?
« Reply #4 on: April 17, 2014, 07:04:22 pm »

Thanks for the confirmation! I tried CAT5 already but since it's not shielded I get too much cross talk between the pairs. The "real" cable people use for this has two individually shielded twisted pairs in one jacket, but it's also about 5x the cost of microphone cable, so even if I have to use twice as much cable, it will still be cheaper.

If you got too much crosstalk it may not have been wired correctly. The twist in CAT cable is very good at eliminating induced noise, and not radiating noise, both of which would minimize crosstalk. FSK is also a low bandwidth, very robust, data transmission scheme that can even be sent wirelessly over walkie talkies. Unless your use involves some special circumstances you haven't mentioned it should work fine. CAT5 is OK with the much less tolerant, much higher bandwidth Ethernet signal.

Mac
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Ivan Beaver

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Re: Are all "microphone" cables generally twisted pair?
« Reply #5 on: April 17, 2014, 08:42:20 pm »

There are different rates of twisting.

For example CATT cable has different twist rates for the different pairs.

This helps reduce crosstalk between pairs.

How much rejection depends on what it is plugged into as much as the twist (give or take).

Balanced also makes a HUGE difference.
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Dan Brandesky

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Re: Are all "microphone" cables generally twisted pair?
« Reply #6 on: April 17, 2014, 09:14:51 pm »

If you got too much crosstalk it may not have been wired correctly. The twist in CAT cable is very good at eliminating induced noise, and not radiating noise, both of which would minimize crosstalk. FSK is also a low bandwidth, very robust, data transmission scheme that can even be sent wirelessly over walkie talkies. Unless your use involves some special circumstances you haven't mentioned it should work fine. CAT5 is OK with the much less tolerant, much higher bandwidth Ethernet signal.

Mac

I think the issue in this particular case is that the line level is actually pretty high, because the modems I'm using are meant for field use, where you may have thousands of feet between "drops". The technician with the company told me that the high line level causes crosstalk very easily between pairs in a regular CAT5 cable, especially since I have both the Rx and Tx pairs within the same CAT5 cable. I could probably get higher quality CAT5 cable, but that's really not much different than using microphone cable -- just different solutions for the same problem.

Jon, I'll check out the Anixter site, I haven't heard of that one. Thanks!
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Mac Kerr

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Re: Are all "microphone" cables generally twisted pair?
« Reply #7 on: April 17, 2014, 09:33:56 pm »

I think the issue in this particular case is that the line level is actually pretty high, because the modems I'm using are meant for field use, where you may have thousands of feet between "drops". The technician with the company told me that the high line level causes crosstalk very easily between pairs in a regular CAT5 cable, especially since I have both the Rx and Tx pairs within the same CAT5 cable. I could probably get higher quality CAT5 cable, but that's really not much different than using microphone cable -- just different solutions for the same problem.

Jon, I'll check out the Anixter site, I haven't heard of that one. Thanks!

The high line level increases the level of crosstalk, but also increases the level relative to the crosstalk,  maintaining the SNR. If you can use FSK over a walkie talkie, and I have to fire fireworks displays, signal to noise is not a critical factor. I think there is something else wrong.

Mac
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Kevin Graf

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Re: Are all "microphone" cables generally twisted pair?
« Reply #8 on: April 19, 2014, 09:55:37 am »

Because mic cable is optimized for rough handling, flexibility and low self-noise when dragged across the stage, it's more expensive than other STP cables.
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Chris Clark

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Re: Are all "microphone" cables generally twisted pair?
« Reply #9 on: April 22, 2014, 08:10:02 pm »

We've been sending AFSK time code over typical "microphone" cables for years without a problem, at a distance of over 400 feet. In fact, at one time, there was an incident which broke one of the cables, and an emergency repair of splicing the two halves together, rather poorly, I might add, the repaired cable still carried FSK without fail for another month.

In all honesty, FSK seems to be more "robust" in terms of ability to transmit time in tough environments than LTC.
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Re: Are all "microphone" cables generally twisted pair?
« Reply #9 on: April 22, 2014, 08:10:02 pm »


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