XLR cable for Rode Lavalier

S

skinheaddave

Member
I have a Rode Lav with an XLR connector. I would like to add a patch cable between the lav and my preamp (which goes to my recorder and then I monitor that). What sort of length can I reasonably add to this mic when running on P48 power without negatively affecting sound quality. I would like to add on about 10-15'.

I realize the better audio situation is to run the preamp and recorder closer to the interview subject and then extend the cable for my headphones out to monitor. That being said, unless the results of my plan above are likely to be disastrous, I really would like to have the dials close at hand during the interview.

Cheers,
Dave
 
Actually, balanced XLR signals from microphones can travel much farther than unbalanced headphone signals, so the way you're wanting to do it is actually the better way. I've never used the Rode lav, but I've used phantom powered mics through as much as 150' of audio snake plus 25-50' of cable between the mic and the snake...
 
An extra fifteen feet is almost nothing. XLR microphone cables carrying phantom power can run several hundred feet at least with no noticeable signal degradation. I used to run just under 1000' of cable all the way around the field when covering college baseball and never had any problems with the audio that I can remember. Just make sure the shielding is good, the cable doesn't have any cuts or kinks in it, and the connectors are properly wired (almost any new commercial cable will be fine).

- GDS
 
The reason XLR (balanced) cables can run so much farther than something like RCA or headphone (unbalanced) cables is because of the extra pin.

In a balanced connection, two copies of the signal are sent. The primary signal, and the same signal 180 degrees out of phase with itself. At the other end, the phase is flipped on the out of phase side, and both signals are put back together. The end result is that any noise that got picked up during the travel through the cable will now be cancelled out. The original signal is reconstructed, and the noise that was picked up along the way gets thrown out of phase with itself.

I've never personally run more than a few hundred feet of XLR cable, but an extra 10 or 15 feet will not hurt the signal at all.
 
Captain Pierce said:
Actually, balanced XLR signals from microphones can travel much farther than unbalanced headphone signals
Click to expand...
I am aware of this -- the issue in my mind was pre-recorder vs. post-recorder noise. Noise introduced into the microphone extension would possibly cause delays while you made sure it was not pre-recorder but would not affect the recorded sound.

Chadfish said:
Rode has an XLR adapter for about 30.00. You need to run phantom through to power the lav. Then just buy a regular XLR cable.
Click to expand...
skinheaddave said:
I have a Rode Lav with an XLR connector.
Click to expand...

robotsound said:
The reason XLR (balanced) cables can run so much farther than something like RCA or headphone (unbalanced) cables is because of the extra pin.
Click to expand...
I am aware of the theory but I'm not entirely sure the lav IS balanced. If the lav isn't (I'm not sure, not seeing it in the spects) then I am skeptical that the micon-->XLR adapter includes a split in the signal, phase reversal etc. that would be needed to go from balanced to unbalanced. That being said, the two relevant pins on the XLR end are not showing any conductivity so they are electrically isolated from each other ... at least in the disconnected state. I suppose I could hook up my osciloscope and figure it out .. but I could probably also just write RODE if I were really dying to know.

All this being said, it does seem that if the RODE mic was designed to be used on P48 power then it likely was meant to be used as with any other mic in that sort of system. The run I want to do is peanuts compared to what you guys are talking about. I'll pick myself up an XLR cable when I am next in the city. You guys have really put my mind at ease. Thanks.

Cheers,
Dave
 
The lav should be balanced. I haven't had personal experience with the Rode lav, but other professional lavs that I seen service technicians put connectors on were balanced.
 
skinheaddave said:
I am aware of the theory but I'm not entirely sure the lav IS balanced. If the lav isn't (I'm not sure, not seeing it in the spects) then I am skeptical that the micon-->XLR adapter includes a split in the signal, phase reversal etc. that would be needed to go from balanced to unbalanced. That being said, the two relevant pins on the XLR end are not showing any conductivity so they are electrically isolated from each other ... at least in the disconnected state. I suppose I could hook up my osciloscope and figure it out .. but I could probably also just write RODE if I were really dying to know.
Click to expand...

The Rode lav is not balanced at the microphone capsule or through the length of the MiCon cable, but the MiCon-5 adapter includes an electronically balanced (transformerless, but still differential) output stage and the circuitry for receiving the P48 power for the mic. Since it's a transistorized differential output circuit, it doesn't work when the adapter isn't powered up and probably wouldn't show any continuity from one pin to another on a meter, but it works fine when 48V is applied. The fact that the mic works on phantom power is itself proof that it's a balanced output signal, since phantom power depends on the differential signal being on the same two pins as the mic power voltage to work.

- Greg
 
There aren't really ANY electret condenser lavs that are truly "balanced" all the way to the head in the common sense of the word*. But the professional (and semi-pro) models use passive (transformer) or active (differential circuit) methods of producing a proper balanced mic-level output. Certainly the Rode Micon-5 XLR adapter works exactly that way.

* To be sure, there are many that use a 2-conductor shielded wire up to the microphone head, but an examination of the circuit shows that typically only one conductor is used for the audio signal, and the other supplies the power to the FET circuit, so it isn't really "balanced".
 
robotsound said:
The reason XLR (balanced) cables can run so much farther than something like RCA or headphone (unbalanced) cables is because of the extra pin.

In a balanced connection, two copies of the signal are sent. The primary signal, and the same signal 180 degrees out of phase with itself. At the other end, the phase is flipped on the out of phase side, and both signals are put back together. The end result is that any noise that got picked up during the travel through the cable will now be cancelled out. The original signal is reconstructed, and the noise that was picked up along the way gets thrown out of phase with itself.

I've never personally run more than a few hundred feet of XLR cable, but an extra 10 or 15 feet will not hurt the signal at all.
Click to expand...

This is an odd way of explaining balanced and it's not really correct.

An audio signal has a +ve and a -ve.

In a balanced cable these are two separate wires and the screen is totally separate. So any interference is picked up equally by both cables and cancels out.

In an unbalanced cable the -ve signal is sent along the screen. As the screen is a different type of cable than the +ve signal cable you do not get full cancellation of any interfering signal and you get interference.

In fact a cable can act like an antenna to pick up radio interference. So an unbalanced cable should be as short as possible. You can run long lengths with balanced cable. Broadcasters mainly use star-quad as this has better cancellation as it has 2 wires for +ve, two wires for -ve and screen. These can run several kilometres across agolf course, for example.
 
To add to John's comments, it is the fact that the inner conductors are twisted together in a spiral form that allows them to reject electromagnetic interference -- this physical configuration insures that interfering signals will enter both conductors at nearly equal levels, and any signal that is common to both leads is ignored at the input circuit, which responds only to the difference in potential between the two wires.

- Greg
 
You must log in or register to reply here.
Back
Top