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Author Topic: How long can I run XLR's without losing quality?  (Read 50252 times)

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Offline fanofthemule

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How long can I run XLR's without losing quality?
« on: November 22, 2009, 10:20:08 AM »
I want to attach some mics to a projector stand that is mounted to a high ceiling.  The only issue I can see with this is that I'd need a lot of XLR cable to be able to get them back to the recorder.  HOw long can you run XLR cable without losing quality?  Is one cable rated better for long runs?
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Re: How long can I run XLR's without losing quality?
« Reply #1 on: November 22, 2009, 11:45:53 AM »
As long as it's balanced and properly shielded, a couple hundred feet should be no problem at all.
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Offline Giant_Rick

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Re: How long can I run XLR's without losing quality?
« Reply #2 on: November 22, 2009, 05:03:34 PM »
A friend of mine who works in a theater says that, in theory, if the cable is balanced it has no limity.. in the real world, he only run a maximum of about 250 meters.
By the way for the taping purpouse, even if distances are not that big, a balanced cable is preferred.. and balancing a cable iss a cheap and easy thing to do :)

Offline willndmb

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Re: How long can I run XLR's without losing quality?
« Reply #3 on: November 22, 2009, 06:29:52 PM »
since we are on the subject
how does one balance a cable?
thanks
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Offline notlance

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Re: How long can I run XLR's without losing quality?
« Reply #4 on: November 22, 2009, 08:21:41 PM »
Assuming you have 200 Ohm mics, and you are using star-quad cable, (which has higher capaticance than single twisted pair cable) you can run about 200 meters before the LPF -3dB point drops below 20kHz.  So for "normal" mic cable, 250 meters is a good max length estimate.

Offline ghellquist

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Re: How long can I run XLR's without losing quality?
« Reply #5 on: November 23, 2009, 01:29:48 AM »
since we are on the subject
how does one balance a cable?
thanks
Standard phantom powered mics are balanced so nothing worry about there.
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Re: How long can I run XLR's without losing quality?
« Reply #6 on: November 23, 2009, 06:42:43 AM »
As long as it's balanced and properly shielded, a couple hundred feet should be no problem at all.
Does it need to be shielded if it is balanced? I'm still learning about the ins and outs of balanced vs unbalanced but I thought that the benefit of a balanced cable is that if interference enters the cable it is rejected at the differential input - as the input only accepts the difference between the two phases, and in theory the interference would show up as the same on both signals.

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Offline mosquito

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Re: How long can I run XLR's without losing quality?
« Reply #7 on: November 23, 2009, 08:03:44 AM »
These may be useful to you:

http://en.wikipedia.org/wiki/Balanced_audio
http://en.wikipedia.org/wiki/Balanced_line


As I understand it, a balanced line does not have to be shielded.  And you understand the purpose / mechanism of balanced lines that allow a way to reject noise that gets picked up.  The shielding just helps keep that amount of noise that can get in lower.

Practically speaking, most mic cables are shielded.  Generically, in a balanced and shielded cable assembly there are three conductors: a pair of wires to carry the signal and a shield that gets connected to ground on both ends.  An unbalanced and shielded cable assembly commonly uses the same general type of cable design -- two wires and a shield -- but the cold wire and the shield are connected electrically, usually inside one or both end connectors.  The shield helps keep noise out of the signal wires but the noise that does get in is prolly going to stay in the output signal since the noise in each of the signal will be different.

And a balanced cable assembly can become unbalanced through damage to the cable or the connectors.  How to test it?  Dunno.  I imagine it would mean sending a bunch of test signals at various frequencies through hot-then-shield and cold-then-shield, measuring the current each time and then verifying that they measure the same.  (If you know the voltage and the current you can calculate the impedance.)

I just try to care of my cables and plan to replace them if they get damaged and I can't cleanly repair them.

Does any of that help?

Offline printguy

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Re: How long can I run XLR's without losing quality?
« Reply #8 on: November 23, 2009, 08:52:54 AM »
These may be useful to you:

http://en.wikipedia.org/wiki/Balanced_audio
http://en.wikipedia.org/wiki/Balanced_line


As I understand it, a balanced line does not have to be shielded.  And you understand the purpose / mechanism of balanced lines that allow a way to reject noise that gets picked up.  The shielding just helps keep that amount of noise that can get in lower.

Practically speaking, most mic cables are shielded.  Generically, in a balanced and shielded cable assembly there are three conductors: a pair of wires to carry the signal and a shield that gets connected to ground on both ends.  An unbalanced and shielded cable assembly commonly uses the same general type of cable design -- two wires and a shield -- but the cold wire and the shield are connected electrically, usually inside one or both end connectors.  The shield helps keep noise out of the signal wires but the noise that does get in is prolly going to stay in the output signal since the noise in each of the signal will be different.

And a balanced cable assembly can become unbalanced through damage to the cable or the connectors.  How to test it?  Dunno.  I imagine it would mean sending a bunch of test signals at various frequencies through hot-then-shield and cold-then-shield, measuring the current each time and then verifying that they measure the same.  (If you know the voltage and the current you can calculate the impedance.)

I just try to care of my cables and plan to replace them if they get damaged and I can't cleanly repair them.

Does any of that help?
Thanks!
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Offline guysonic

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Re: How long can I run XLR's without losing quality?
« Reply #9 on: November 23, 2009, 12:59:10 PM »
 
Long cable running audio has several issues to consider. While balanced cable more or less does cancel induced noise inerference working best if mic output impedance is <1000 ohms, there is a concern that cables used for audio these days are not terminated in the cable's characteristic impedance.

If this were video cable with no terminated impedance resistance at the receiving end, the video would appear smeared with video artifacts as the original information would arrive from the original at different times and not simultaniously as it should. Also, multibles of the original video would also arrive as an unterminated cable relects back some of the original to bounce back and forth between the source and receving end.

With video, these artifacts with unterminated cable is quite visible and worsens with length.

Used to be audio cable was rated at 600 ohms impedance and always terminated with a 600 ohm termination at the reeceiving end so information delays and reflection artifacts where minimized.


While these issues still existwith both video and audio, it's only video (and now digital feeds) that is still terminated in the cable's characteristic impedances (75, 50, 300 or some other impedance appropriate for the cable type being used.


Over the years I nd others have done listening tests determining unterminated cable with as little as 1 meter lengths are effected with audible artifacts if not terminated in a low impedance and driven by a source capable of high driving power.

The problem is audio cable these days usually does not have stated cable impedance and if it does it's very low (<150 ohms) requiring being driven and terminated low a matching <150 ohm resistance.  Some microphones do have such low output impedance, but most IC audio output amplifiers have difficulty driving such loads especially long complex impedance cable types requiring matching output transformers having their own audio quality limitations or considerations besides be costly for the better designed ones so not a good solution in general.
Suggest knowing what the microphone driving impedance is and terminating the receiving end of long runs of cable with close to this to minimize the effects of unterminated audio cable.  If balanced type, then a single resistor connecting the two signal leads is sufficient.  If unbalanced (like coax) then place the termination resistor from signal to ground common at the receiving end.
Many years ago recording engineers at I believe called B&K figured this out and used 50 and 75 ohm coax driving preamplifiers to drive terminated cable at hundreds of feet distances eliminating all cable artifacts in the audio.   I have done the same with a stereo preamplifier design driving up to several thousands of foot lengths of terminated S-VHS cable that also eliminates all cable artifacts delivering pristine audio regardless of distances. 

See the S-VHS cable driving preamplifier on my site's accessory page:
http://www.sonicstudios.com/access.htm#24njv

   
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Offline Giant_Rick

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Re: How long can I run XLR's without losing quality?
« Reply #10 on: November 23, 2009, 03:53:03 PM »
As long as it's balanced and properly shielded, a couple hundred feet should be no problem at all.
Does it need to be shielded if it is balanced?
I'm not an expert, but as far as I know, it doesn't need to be shielded.
In fact having a balanced cable means having the same signal running in one cable in its phase, and another signal running out of phase by 90°; I think that if you can ''take'' those two signals togheter you would hear nothing as a signal 'cancel' the other one.
So cables can pick some noisy signals, but when they are into the recorder/preamp/whatever, the out-of-phase signal is 'switched' to the same phase of the original, so the signal is stronger and the noise is cancelled.
But in reality I think a shielding is preferred.

Offline Patrick

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Re: How long can I run XLR's without losing quality?
« Reply #11 on: November 23, 2009, 04:44:26 PM »
As long as it's balanced and properly shielded, a couple hundred feet should be no problem at all.
Does it need to be shielded if it is balanced?
I'm not an expert, but as far as I know, it doesn't need to be shielded.
In fact having a balanced cable means having the same signal running in one cable in its phase, and another signal running out of phase by 90°; I think that if you can ''take'' those two signals togheter you would hear nothing as a signal 'cancel' the other one.
So cables can pick some noisy signals, but when they are into the recorder/preamp/whatever, the out-of-phase signal is 'switched' to the same phase of the original, so the signal is stronger and the noise is cancelled.
But in reality I think a shielding is preferred.

This is correct; a balanced cable and a shielded cable are two different things.  A shielded cable certainly helps with reducing noise and interference, which is exactly what a balanced cable does as well.  Sometimes you'll see individual unshielded wires in multicore snakes, but they almost always have an outer shield that covers the whole bunch of cables. 

Shielding is definitely preferred.   :)

Offline willndmb

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Re: How long can I run XLR's without losing quality?
« Reply #12 on: November 25, 2009, 01:40:16 PM »
since we are on the subject
how does one balance a cable?
thanks
Standard phantom powered mics are balanced so nothing worry about there.
Gunnar
thanks
i am thinking more of speaker runs though
from a mixer to powered speakers for example
Mics - AKG ck61/ck63 (c480b & Naiant actives), SP-BMC-2
XLR Cables - Silver Path w/Darktrain stubbies
Interconnect Cables - Dogstar (XLR), Darktrain (RCA > 1/8) (1/8 > 1/8), and Kind Kables (1/8f > 1/4)
Preamps - Naiant Littlebox & Tinybox
Recorders - PCM-M10 & DR-60D

Offline Patrick

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Re: How long can I run XLR's without losing quality?
« Reply #13 on: November 25, 2009, 02:09:24 PM »
since we are on the subject
how does one balance a cable?
thanks
Standard phantom powered mics are balanced so nothing worry about there.
Gunnar
thanks
i am thinking more of speaker runs though
from a mixer to powered speakers for example

It doesn't matter if your cables are balanced if your input/output on each device you're using is unbalanced.  Speaker cables are generally unbalanced, since they are two conductor (+/-) cables and are not connected to ground.  Also since speaker cables are carrying a signal that is measured in actual volts, the signal is much stronger compared to a microphone cable and the risk of noise and interference is lower.  Therefore it's not a huge concern to have a long run of unbalanced speaker cable.

 

Offline Church-Audio

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Re: How long can I run XLR's without losing quality?
« Reply #14 on: December 03, 2009, 09:19:32 AM »
I want to attach some mics to a projector stand that is mounted to a high ceiling.  The only issue I can see with this is that I'd need a lot of XLR cable to be able to get them back to the recorder.  HOw long can you run XLR cable without losing quality?  Is one cable rated better for long runs?

Hi I run cable lengths of 300 feet to 450 feet all the time at a concert. There is going to be very little degradation at that distance if your using a quality cable.

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