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Author Topic: 2-wire comms nulling question  (Read 5721 times)

brian maddox

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2-wire comms nulling question
« on: January 28, 2016, 12:44:28 pm »

Okay, Peter, this one is for you.  :)

I'm encountering an issue quite a lot on show sites recently so i'm hoping you can shed some light on best practices in this situation.

I've got a Model 45A 4-wire to 2-wire interface between a Clearcom Matrix system and a wired TW Clearcom analog system.  Both channels of the Model 45A are being used to the TW analog system.  I've also got an HME DX210 system interfaced into the same TW Clearcom analog system using a TW701 interface to breakout the TW channels to two Single Clearcom channels.  I've got a two channel Clearcom power supply hanging off the whole rig to supply power for all the local TW belt packs.

Because the Clearcom Eclipse Matrix is being used over the inter webs, it is imperative that i get the maximum amount of nulling in the local 2-wire analog system to prevent very annoying echo to the matrix users.

Once everything is hooked up and operational, what should my nulling procedure be?  Both the HME and the Model 45A have excellent auto-nulling capability, but i'm not sure which to do first or why.  Also, would it be better to use the 4-wire capability of the HME to remove that issue from the equation?

Any guidance would be much appreciated.

FWIW, i also often do this exact same setup, but with a Tempest system in place of the HME.

Thanks in advance.

brian
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brian maddox
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Chris Johnson [UK]

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Re: 2-wire comms nulling question
« Reply #1 on: January 29, 2016, 03:26:59 am »

I'm going to jump in here, because why not!

First off, wrong forum! But I'm sure someone can move it.

I would definitely remove the 2W HME interface. Go 4W. By using the 2wire, you are unnecessarily adding another hybrid to the equation, and another point for less-than-perfect nulling.

Once you've done this, you simply null the 2W system on the 45A once all the 2W elements are connected.
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Pete Erskine

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Re: 2-wire comms nulling question
« Reply #2 on: January 29, 2016, 01:45:08 pm »

I'm going to jump in here, because why not!

First off, wrong forum! But I'm sure someone can move it.

I would definitely remove the 2W HME interface. Go 4W. By using the 2wire, you are unnecessarily adding another hybrid to the equation, and another point for less-than-perfect nulling.

Once you've done this, you simply null the 2W system on the 45A once all the 2W elements are connected.

Ditto
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Pete Erskine
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Pete Erskine

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Re: 2-wire comms nulling question
« Reply #3 on: January 29, 2016, 01:49:27 pm »

I've got a Model 45A 4-wire to 2-wire interface between a Clearcom Matrix system and a wired TW Clearcom analog system.  Both channels of the Model 45A are being used to the TW analog system.

How many TW Beltpacks are you using and what channels do you have interfaced?

You also are using a TW701 to make your TW channel, right?
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brian maddox

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Re: 2-wire comms nulling question
« Reply #4 on: January 29, 2016, 02:23:16 pm »

How many TW Beltpacks are you using and what channels do you have interfaced?

You also are using a TW701 to make your TW channel, right?

Number of TW belt packs varies but usually less than a 12.  There's also a Model233 announcer console in the system [my personal comm station].

The scenario i listed above basically is the same two channels on everything.  So it's channel A and B on the Model45, connected to A and B on the TW system, and A and B on the HME.  There are times it gets more convoluted, but this is the most frequent configuration.

And yes i'm using a TW701 to make the TW channel for both the belt packs and the Model45.
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brian maddox
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brian maddox

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Re: 2-wire comms nulling question
« Reply #5 on: January 29, 2016, 02:33:52 pm »

I'm going to jump in here, because why not!

First off, wrong forum! But I'm sure someone can move it.

I would definitely remove the 2W HME interface. Go 4W. By using the 2wire, you are unnecessarily adding another hybrid to the equation, and another point for less-than-perfect nulling.

Once you've done this, you simply null the 2W system on the 45A once all the 2W elements are connected.

Yeah, as soon as i posted it i realized i had both minimized others potential knowledge in this area AND put it into the wrong forum.  Oops times two.  Thanks for jumping in anyway.  :)

So if i go 4W on the HME system, how do i go about interfacing that 4W 'channel' with the 4W 'channel' from my matrix panel?  This feels like a stupid question even as i'm typing it, but i guess i've just not worked a lot with 4W.  i certainly understand that in theory this is a simple 2into1 passive mixer and a 1into2 splitter, but i'm not sure if there is a device or best practice that is usually used to accomplish this task.

To be clear, i would want these two 4W 'channels' to be on the same physical Partyline with one another.  The Matrix frame is not local so simply putting the two 4W systems into two ports on the matrix and creating whatever connection i need in there is not an option.
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"It feels wrong to be in the audience.  And it's too peopley!" - Steve Smith

brian maddox
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Pete Erskine

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Re: 2-wire comms nulling question
« Reply #6 on: January 29, 2016, 06:54:51 pm »

So if i go 4W on the HME system, how do i go about interfacing that 4W 'channel' with the 4W 'channel' from my matrix panel?  This feels like a stupid question even as i'm typing it, but i guess i've just not worked a lot with 4W.  i certainly understand that in theory this is a simple 2into1 passive mixer and a 1into2 splitter, but i'm not sure if there is a device or best practice that is usually used to accomplish this task.

To be clear, i would want these two 4W 'channels' to be on the same physical Partyline with one another.  The Matrix frame is not local so simply putting the two 4W systems into two ports on the matrix and creating whatever connection i need in there is not an option.

Just connect each of the 4W to the same Party line.  I don't see why that is not an option.  It's how it is always done.  Do you have programming access to the Matrix?  What model is it, Matrix Plus II" or Eclipse?

If you have access to only 1 4-wire to the party line and you need to add several 4Wire to that party lin you need something to do a mix minus of each 4 wire.  See the mic minus settings on a 3X3 micer - each does not hear itself but hears the other 2.
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Pete Erskine
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Pete Erskine

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Re: 2-wire comms nulling question
« Reply #7 on: January 29, 2016, 07:04:50 pm »

Number of TW belt packs varies but usually less than a 12.  There's also a Model233 announcer console in the system [my personal comm station].

The scenario i listed above basically is the same two channels on everything.  So it's channel A and B on the Model45, connected to A and B on the TW system, and A and B on the HME.  There are times it gets more convoluted, but this is the most frequent configuration.

And yes i'm using a TW701 to make the TW channel for both the belt packs and the Model45.

Getting down to 1 Hybrid is the best way to minimize cross talk.  It won't be totally gone.  Using the shortest amount of mic cable will improve the null.   run 1-100' with Y on end rather than 2-100'.

Also do not use Star Quad cable.  This increases cross talk on 2 channel comm wiring and makes the null poor.
« Last Edit: January 30, 2016, 06:35:46 pm by Pete Erskine »
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brian maddox

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Re: 2-wire comms nulling question
« Reply #8 on: January 30, 2016, 01:53:21 pm »

Just connect each of the 4W to the same Party line.  I don't see why that is not an option.  It's how it is always done.  Do you have programming access to the Matrix?  What model is it, Matrix Plus II" or Eclipse?

As usual i've done a very poor job of actually describing my situation.  So i'll try again.

The ClearCom Eclipse matrix is located in a Master Control Studio in Washington DC.  Live shows are broadcast through that location from all over the world.  On the local show site [which again, can be anywhere], interface to the Eclipse system is accomplished over IP using a V-series panel locally and an IVC-32 card in the Matrix.  This panel gives me one fully functional matrix panel PLUS two individual 4W ports back to the Matrix frame.  Typically the desire is to have those two 4W ports be on two separate party lines with the two local analog PLs.  Those local analog PLs usually include a mixture of wired and wireless.  So each 4W port coming from the matrix needs to be connected to both a wireless AND a wired analog system. 

In the past i have simply converted 4W to 2W and then put both wireless and wired on the 2W.  But that has made nulling difficult.  And because of the inherent latency in an IP connection going across the world, poor nulling presents as very audible and annoying echo to my matrix panel users in DC and elsewhere.

And yes i have full programming access to the Matrix from show site using Teamviewer to screenshare back to the Eclipse configuration computer in DC.

If you have access to only 1 4-wire to the party line and you need to add several 4Wire to that party lin you need something to do a mix minus of each 4 wire.  See the mic minus settings on a 3X3 micer - each does not hear itself but hears the other 2.

This is what i suspected and i fully understand the principles involved. I do think that using 4W for my HME and Tempest systems is the best way to go.  So, In the above 3X3 scenario or something similar, do you have a favorite product you like to use to accomplish this? 
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brian maddox
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'...do not trifle with the affairs of dragons...

       ....for you are crunchy, and taste good with ketchup...'

brian maddox

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Re: 2-wire comms nulling question
« Reply #9 on: January 30, 2016, 01:56:47 pm »

Getting down to 1 Hybrid is the best way to minimise cross talk.  It won't be totally gone.  Using the shortest amount of mic cable will improve the null.

Also do not use Star Quad cable.  This increases cross talk on 2 channel comm wiring and makes the null poor.

This little golden nugget is why i asked this question here.  I did not know that Star Quad made TW systems more susceptible to crosstalk, although i can understand why just by thinking about it for a second.  The client i am doing this work for SWEARS by Star Quad [for the record i do not] and i suspect ALL the wire i have been using is Star Quad.  So it looks like i need them to make/buy me some dedicated comms cables that are NOT Star Quad. 
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"It feels wrong to be in the audience.  And it's too peopley!" - Steve Smith

brian maddox
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       ....for you are crunchy, and taste good with ketchup...'

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Re: 2-wire comms nulling question
« Reply #9 on: January 30, 2016, 01:56:47 pm »


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