XLR Cable length

R Geoff Baker · December 11th, 2006, 08:00 AM

AFAIK, the Canon XLR adapters didn't include phantom power, but I've not used them so if I'm wrong someone can correct me here -- but also AFAIK all XLR connections are 'balanced' -- the only way they would be otherwise is if for some bizarre reason one of the wires was left unconnected ... which would rather defeat the whole point!

Which takes us back to the original query: Why would XLR cable length be restricted to 3 metres -- no reason I can imagine, and quite contrary to the whole point of XLR cabling; with XLR cables you can enjoy noise free (or nearly so) mic cabling for long runs -- with unbalanced cables, even five metres can introduce noises that can render your audio useless.

HTH

GB

Simon Dean · December 11th, 2006, 10:55 AM

I agree - the whole point of XLR is balanced cables. However, it is possible to mess it up and not only leave a wire off but have it reversed which can be a nightmare.

A condensing mic with phantom power of XLR should go a long way. I've done 30 metres no problem.

If wiring your own connectors, be careful with phantom power and the correct polarity of the wires!

Jerome Marot · December 11th, 2006, 11:14 AM

Thanks to all who replied. I tried my own XLR cables without problems (10 meters), but I really wondered about this phrase in the manual. So, apparently, it is simply an error.

Carlos E. Martinez · December 11th, 2006, 01:44 PM

Quote:

Originally Posted by R Geoff Baker

I can only assume you to mean because the XL1 without the XLR adapter had no XLR inputs were the inputs unbalanced -- when you added the required XLR adapter (either the MA-100 or the MA-200) then you had balanced XLR inputs on a Canon XL1 ... otherwise, you had no XLR inputs on an XL1.

Is that what you mean?

Yes, the XL1 or XL1s had unbalanced inputs.

The adapter was optional, not included. Very much like a Sony FX1 now or even the Canon GL2.

When you included an adaptor, by them or Beachtek, you got balanced inputs.

The preamp specs were not so great, and it was a bit expensive for what you got. I know that because in those times I released a mic preamp I designed, and had a few Canon customers.

Carlos E. Martinez · December 11th, 2006, 01:56 PM

Quote:

Originally Posted by R Geoff Baker

AFAIK, the Canon XLR adapters didn't include phantom power, but I've not used them so if I'm wrong someone can correct me here

No, neither of the adaptors had phantom power.

Quote:

-- but also AFAIK all XLR connections are 'balanced' -- the only way they would be otherwise is if for some bizarre reason one of the wires was left unconnected ... which would rather defeat the whole point!

You can do what it's called a "fake balanced" connection and use a XLR for sturdiness and universality. You wired small resistors to hot pin and from cold pin to ground, and voilá: the other side sees a balanced connection. Or you wire cold pin to ground for a single wire/shield connection.

But of course, most XLR connections are usually balanced. Just not automatically so...

Jim Michael · December 11th, 2006, 07:57 PM

Since it is important to understand the reason for using balanced cables in an application I made a quick review of the Yamaha Sound Reinforcement Handbook*. Here is very brief summary:

Shielding protects the signal from electrostatic interference. Defects (openings, gaps , cracks) in the shielding can allow noise from electrostatic sources. Electromagnetic interference (such as from electric motors or fluorescent light ballasts) enters cable via inductive coupling and is not stopped by normal shielding. Magnetic fields are only cancelled by balanced lines. Another item of concern is cable self-capacitance. Shielding results in capacitance and the cable's constant resistance combined with the capacitance results in a low pass filter; the greater the capacitance per foot and the longer the cable, the lower the cutoff frequency of the filter.

*ISBN 0-88188-900-8

Chris Hocking · December 11th, 2006, 08:33 PM

Sorry Carlos! I was under the impression that the MA-100 came standard with the XL1, hence the reason why I said the XL1 has balanced inputs (ignoring the fact that those balanced inputs are then converted to unbalanced before reaching the camera). Sorry mate - you are absolutely right - the actual inputs on the camera are indeed UNBALANCED (but be aware they are RCAs and NOT XLRs - a RCA only has 2 pins and thus has to be unbalanced).

I don't really see the point of a "fake balanced" cable as you described. Actually, I don't even see how it would work to be perfectly honest. All a resister does is resists an electric current by producing a voltage drop between its terminals (in accordance with Ohm's law) - so wouldn't connecting the hot and cold together even with in-line resisters still create a "smaller" short circuit? You've lost me on that one!

And yes, you're right. Most XLR connectors/cables are balanced - but NOT automatically so.

XLR is just a name for the type of connector. It was originally the Cannon X series, subsequent versions added a Latch - Cannon XL - and then a Rubber compound surrounding the contacts, which led to the acronym XLR). Although some people believe it really means eXternal Left Right or eXternal Live Return, which works, but historically, I think it's named by Cannon (now part of ITT). Anyway! XLRs can have various numbers of pins. 3-pin is normally used for balanced audio, 5-pin for lighting DMX and 4-pin for intercom systems. However, you can have 3-pin DMX and 6-pin stereo audio. Anyway, XLR is just the name of the type of connector - it doesn't specify anything about the intended use for the connector.

However, there is a EIA Standard for Balanced Audio Cable (using XLR adapters) - RS-297-A. It states:

Wiring
Pin 1 - Ground
Pin 2 - Hot
Pin 3 - Cold

Connectors
XLR3M (Male) is used for Output and XLR3F (Female) for input.

There is NO standard for unbalanced cables using XLR connectors.

So yes Jerome, Sony just made a mistake or took the attitude "better to be safe than sorry" when writing that documentation. As far as I know there is no writing specification to the maximum length of a XLR cable, so really Sony can say anything they want.

Now, although cables can vary - the wiring can be phase reversed, etc. I have NEVER seen an unbalanced XLR connector on a piece of gear. It just doesn't make any sense technically (you can ignore 1 pin) or financially (RCA, 3.5mm Jacks etc. are so much cheaper and require less time to install). If someone knows of a unbalanced XLR connection on a mixer, outboard piece of gear, etc. I'd love to hear from them!

Who would have thought such a simple mistake from Sony could have sparked up such an interesting topic!

Chris!

Related Post: http://dvinfo.net/conf/showthread.php?t=46613

Chris Hocking · December 11th, 2006, 08:40 PM

Oh, and you can also have XLR-LNE connectors which are traditionally used for power on mixers, outboard gear, etc. I haven't seen them around for a while - I think they've been mostly replaced by IECs (at least in Australia anyway).

Speaker cable used to use 3-pin XLRs as well (and still do), however instead of male for output they do the reverse. Most newer speakers use the Neutrik Speakon connector though...

Chris!

Carlos E. Martinez · December 12th, 2006, 05:03 AM

This whole XLR thing is very interesting and may have more applications than most people foresee.

Chris view that XLR and balance were almost the same thing is a very common idea, that I can't say I didn't have it myself in my first years as an audio recordist. Back then there were only 3-pin XLRs. Now you have 4, 5 and 6 pin types that you can find anywhere.

And they are great connectors, because they lock when connected and the cable is quite well secured.

So much so that I have used them on many applications to avoid plugging/unplugging other types. This is a very important issue to think on.

In video we deal with many fragile connectors, that are like a "clicking bomb" sometimes. Like camera's headphone/mic 1/8" jacks, AC power supply and 1394.

What I do, to diminish the "clicking effect" is use short cable adaptors. For headphones: 1/8" plug to 1/4" jack adaptors. For mic inputs: 1/8" to two XLR-3 adaptors. For AC: I cut the original AC cable and put XLR-4 cable connectors in between. For firewire: I cut the original cable and put a XLR-4 or XLR-6 pair in between.

At home I also use XLR-4 connectors pairs on S-video cables, as a way to diminish potential bad contacts.

Carlos E. Martinez · December 12th, 2006, 05:24 AM

Quote:

Originally Posted by Chris Hocking

Speaker cable used to use 3-pin XLRs as well (and still do), however instead of male for output they do the reverse. Most newer speakers use the Neutrik Speakon connector though...

3-pin XLRs on commercial equipment, particularly amplifiers or speakers, should be restricted (and usually are) to low signal level inputs or outputs.

The Speakon should be the connector of choice for speakers input.

Somsack Vilaysack · December 20th, 2006, 02:38 PM

I was also wondering about the cable length recommendation in the A1 manual, so I e-mailed Canon support to ask about it. This is their response:

"This limitation was suggested because there may be signal fall off with
longer cables, although as you pointed out, it is common for much
longer cables to be used. It just indicates the signal strength may not be as
strong as with shorter cables. I am sorry for any confusion."

Don Palomaki · December 20th, 2006, 08:44 PM

The cable length issue comes into play with high impedance mics/connections, as was common with consumer gear up until very recently. Typical impedances were 50K ohms and higher, resulting in lots of high frequency signal fall off due to cable capacitance. This typicall y became a significant issue around 20 feet (~6 meters) or so. High impedance also made it easier for electrostatic and magnetic coupling of stray signals into the cable.

Balanced lines use a combination of transposition (twist) coupled with +/- input a tthe preamp and low impedance to provide noise cancellation and reduced noise coupling, as well as reduced losses due to cable capacitance. A side benefit is the ability to provide phantom power. The nosie cancellation at the preamp input is thanks to common mode rejection of balanced input.

The mic level inputs on the XL1 and XL1s are unbalanced 600 ohm. The MA-100/300 provide balanced-to-unbalanced conversion and 6 dB of gain. The short leads fromt the adapter to the XL1 minimized the chance of stray noise pickup.

You can buy cheap XLR adapters that effectively unbalance a balanced XLR source by grounding pin 3. Typically these provide an XLR-to-RCA connction. This effectively kills the common mode cancellation benefit and ability to use phantom power, but the benefits of transposition in the cable and low impedance are retained.

Some single point stereo mics use a 5-pin XLR connector at the mic; e.g., the AT-825 and the Sony ECM-MS957.

December 12th, 2006, 05:03 AM	#24
Carlos E. Martinez Trustee Join Date: Oct 2003 Location: Rio de Janeiro, Brasil Posts: 1,138	XLR connectors This whole XLR thing is very interesting and may have more applications than most people foresee. Chris view that XLR and balance were almost the same thing is a very common idea, that I can't say I didn't have it myself in my first years as an audio recordist. Back then there were only 3-pin XLRs. Now you have 4, 5 and 6 pin types that you can find anywhere. And they are great connectors, because they lock when connected and the cable is quite well secured. So much so that I have used them on many applications to avoid plugging/unplugging other types. This is a very important issue to think on. In video we deal with many fragile connectors, that are like a "clicking bomb" sometimes. Like camera's headphone/mic 1/8" jacks, AC power supply and 1394. What I do, to diminish the "clicking effect" is use short cable adaptors. For headphones: 1/8" plug to 1/4" jack adaptors. For mic inputs: 1/8" to two XLR-3 adaptors. For AC: I cut the original AC cable and put XLR-4 cable connectors in between. For firewire: I cut the original cable and put a XLR-4 or XLR-6 pair in between. At home I also use XLR-4 connectors pairs on S-video cables, as a way to diminish potential bad contacts.

December 20th, 2006, 08:44 PM	#27
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,489	The cable length issue comes into play with high impedance mics/connections, as was common with consumer gear up until very recently. Typical impedances were 50K ohms and higher, resulting in lots of high frequency signal fall off due to cable capacitance. This typicall y became a significant issue around 20 feet (~6 meters) or so. High impedance also made it easier for electrostatic and magnetic coupling of stray signals into the cable. Balanced lines use a combination of transposition (twist) coupled with +/- input a tthe preamp and low impedance to provide noise cancellation and reduced noise coupling, as well as reduced losses due to cable capacitance. A side benefit is the ability to provide phantom power. The nosie cancellation at the preamp input is thanks to common mode rejection of balanced input. The mic level inputs on the XL1 and XL1s are unbalanced 600 ohm. The MA-100/300 provide balanced-to-unbalanced conversion and 6 dB of gain. The short leads fromt the adapter to the XL1 minimized the chance of stray noise pickup. You can buy cheap XLR adapters that effectively unbalance a balanced XLR source by grounding pin 3. Typically these provide an XLR-to-RCA connction. This effectively kills the common mode cancellation benefit and ability to use phantom power, but the benefits of transposition in the cable and low impedance are retained. Some single point stereo mics use a 5-pin XLR connector at the mic; e.g., the AT-825 and the Sony ECM-MS957. __________________ dpalomaki@dspalomaki.com

December 11th, 2006, 08:00 AM	#16
R Geoff Baker Major Player Join Date: Jan 2005 Location: Ottawa, ON Posts: 471	AFAIK, the Canon XLR adapters didn't include phantom power, but I've not used them so if I'm wrong someone can correct me here -- but also AFAIK all XLR connections are 'balanced' -- the only way they would be otherwise is if for some bizarre reason one of the wires was left unconnected ... which would rather defeat the whole point! Which takes us back to the original query: Why would XLR cable length be restricted to 3 metres -- no reason I can imagine, and quite contrary to the whole point of XLR cabling; with XLR cables you can enjoy noise free (or nearly so) mic cabling for long runs -- with unbalanced cables, even five metres can introduce noises that can render your audio useless. HTH GB

December 11th, 2006, 10:55 AM	#17
Simon Dean Regular Crew Join Date: Oct 2006 Location: Coventry, UK Posts: 91	I agree - the whole point of XLR is balanced cables. However, it is possible to mess it up and not only leave a wire off but have it reversed which can be a nightmare. A condensing mic with phantom power of XLR should go a long way. I've done 30 metres no problem. If wiring your own connectors, be careful with phantom power and the correct polarity of the wires!

December 11th, 2006, 11:14 AM	#18
Jerome Marot Regular Crew Join Date: Jul 2006 Location: Munich (Germany) Posts: 107 Images: 4	Thanks to all who replied. I tried my own XLR cables without problems (10 meters), but I really wondered about this phrase in the manual. So, apparently, it is simply an error.

December 11th, 2006, 07:57 PM	#21
Jim Michael Major Player Join Date: Dec 2005 Posts: 895	Since it is important to understand the reason for using balanced cables in an application I made a quick review of the Yamaha Sound Reinforcement Handbook. Here is very brief summary: Shielding protects the signal from electrostatic interference. Defects (openings, gaps , cracks) in the shielding can allow noise from electrostatic sources. Electromagnetic interference (such as from electric motors or fluorescent light ballasts) enters cable via inductive coupling and is not stopped by normal shielding. Magnetic fields are only cancelled by balanced lines. Another item of concern is cable self-capacitance. Shielding results in capacitance and the cable's constant resistance combined with the capacitance results in a low pass filter; the greater the capacitance per foot and the longer the cable, the lower the cutoff frequency of the filter. ISBN 0-88188-900-8

December 11th, 2006, 08:33 PM	#22
Chris Hocking Major Player Join Date: Dec 2005 Location: Melbourne, Australia Posts: 595	Sorry Carlos! I was under the impression that the MA-100 came standard with the XL1, hence the reason why I said the XL1 has balanced inputs (ignoring the fact that those balanced inputs are then converted to unbalanced before reaching the camera). Sorry mate - you are absolutely right - the actual inputs on the camera are indeed UNBALANCED (but be aware they are RCAs and NOT XLRs - a RCA only has 2 pins and thus has to be unbalanced). I don't really see the point of a "fake balanced" cable as you described. Actually, I don't even see how it would work to be perfectly honest. All a resister does is resists an electric current by producing a voltage drop between its terminals (in accordance with Ohm's law) - so wouldn't connecting the hot and cold together even with in-line resisters still create a "smaller" short circuit? You've lost me on that one! And yes, you're right. Most XLR connectors/cables are balanced - but NOT automatically so. XLR is just a name for the type of connector. It was originally the Cannon X series, subsequent versions added a Latch - Cannon XL - and then a Rubber compound surrounding the contacts, which led to the acronym XLR). Although some people believe it really means eXternal Left Right or eXternal Live Return, which works, but historically, I think it's named by Cannon (now part of ITT). Anyway! XLRs can have various numbers of pins. 3-pin is normally used for balanced audio, 5-pin for lighting DMX and 4-pin for intercom systems. However, you can have 3-pin DMX and 6-pin stereo audio. Anyway, XLR is just the name of the type of connector - it doesn't specify anything about the intended use for the connector. However, there is a EIA Standard for Balanced Audio Cable (using XLR adapters) - RS-297-A. It states: Wiring Pin 1 - Ground Pin 2 - Hot Pin 3 - Cold Connectors XLR3M (Male) is used for Output and XLR3F (Female) for input. There is NO standard for unbalanced cables using XLR connectors. So yes Jerome, Sony just made a mistake or took the attitude "better to be safe than sorry" when writing that documentation. As far as I know there is no writing specification to the maximum length of a XLR cable, so really Sony can say anything they want. Now, although cables can vary - the wiring can be phase reversed, etc. I have NEVER seen an unbalanced XLR connector on a piece of gear. It just doesn't make any sense technically (you can ignore 1 pin) or financially (RCA, 3.5mm Jacks etc. are so much cheaper and require less time to install). If someone knows of a unbalanced XLR connection on a mixer, outboard piece of gear, etc. I'd love to hear from them! Who would have thought such a simple mistake from Sony could have sparked up such an interesting topic! Chris! Related Post: http://dvinfo.net/conf/showthread.php?t=46613

December 11th, 2006, 08:40 PM	#23
Chris Hocking Major Player Join Date: Dec 2005 Location: Melbourne, Australia Posts: 595	Oh, and you can also have XLR-LNE connectors which are traditionally used for power on mixers, outboard gear, etc. I haven't seen them around for a while - I think they've been mostly replaced by IECs (at least in Australia anyway). Speaker cable used to use 3-pin XLRs as well (and still do), however instead of male for output they do the reverse. Most newer speakers use the Neutrik Speakon connector though... Chris!

December 20th, 2006, 02:38 PM	#26
Somsack Vilaysack New Boot Join Date: Dec 2006 Location: Long Beach, CA Posts: 5	I was also wondering about the cable length recommendation in the A1 manual, so I e-mailed Canon support to ask about it. This is their response: "This limitation was suggested because there may be signal fall off with longer cables, although as you pointed out, it is common for much longer cables to be used. It just indicates the signal strength may not be as strong as with shorter cables. I am sorry for any confusion."