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2 balanced outputs to 1 balanced mono input cable
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b_dann_b
Presonic
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Joined: 09/03/2011 13:03:37
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Hi Guys,

need some expert advice on something i thought was pretty straight forward but have now found is not...

Background:
just scored a set of NEXO speakers - 4 PS10s and 2 LS500 subs. Am in the process of getting 2 Camco Tecton 38.4 amps and the NEXO PS10 TD controller thats required for them. For those unfamiliar with the speakers, it is strongly advised that you use the NEXO controller to run these speakers as they apparently sound crap without them.

Because of the set, there are multiple ways that the system can be run/used - 2 PS10s, 2 PS10s and 1 sub, 2 PS10s and 2 Subs, 4 PS10s for foldback, 4 PS10s and 2 subs. Depending on the combination i can run them off 1 or 2 of the amps, or have up to 2 separate rigs for hire which makes it very versatile.

So here's the the query:

In a 2 PS10/1 sub scenario i can run this off 1 amp with channel A doing the PS10s in mono and channel B doing the sub. The NEXO controller has Left and Right balanced inputs and then Left, Right and Sub Outputs (the sub output can either be a sum of L+R or R depending on how you setup the jumpers inside the controller). Sub is easy, sub out to one of the inputs of the amp. L and R, not so easy (so it seems).

I want to combine the L and R outs of the controller (balanced XLR) to 1 male balanced XLR to go into the other channel of the amp so that the PS10s run in summed mono. I want to do this in a cable. Here's my few dilemma's:

1. if i just use the L channel then if someone pans on the mixer to the right then it wont come out in the speakers... thus summing.
2. If i just use the R channel then same as above.
3. everything i've read says it not as simple as just using a Y (wye - google this and it will make more sense) apparently you need to put resistors in series with the hot and cold pins of both outputs before you can combine them.

So my actual questions:
1. is 3 correct? i need to use resistors to make this cable?
2. if so, which ones? is it dependent on the devices themselves?
3. how do i actually wire it? can someone draw a diagram?
4. what do i need to consider if i do it this way? are there alternative options?


There are a handful of sites that talk about this issue:
- the source of it all is a RANE site: http://www.rane.com/note109.html
- but it is then discussed in this site where 2 people state that the RANE wording is right, but the diagram is wrong: http://forum.speakerplans.com/how-to-make-a-balanced-mono-sum-cable_topic50418.html
- this one is a bit more useful, but then says that if you do this in a passive cable then you get 6db of signal loss: http://www.gearslutz.com/board/geekslutz-forum/32861-stereo-mono-summing.html

Any other suggestions would be most welcome.

Thanks


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lowdbrent
Presonic
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Joined: 13/11/2010 22:17:51
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No, you cannot just sum L and R to make mono. You need a resister in there. You would basically be shorting the two outputs together. You would also me hurting yourself, creating some phase issues. If you are going to one mono input, why not start with one mono output?

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b_dann_b
Presonic
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Joined: 09/03/2011 13:03:37
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a mono output from the desk or from the controller to the amp?

From the desk - i can do this for myself ,but i'm making this available for hire and don't want to assume that the user has a mono out.
From the controller - i'm not sure if just using the left channel will give a true mono out i.e. using left only sums the left and right for me. this would be the ideal situation as its less screwing around for me.

The controller manual (http://nexo-sa.com/attachments/products/46/ps-series-manual.pdf) doesn't explicitly say anything about mono (summed) on the left channel. Might have to get in contact with the distributor and check.

Any more options are most welcome.
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gadget69
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Not sure if you realize it or not but with the pan control centered on the channels you essentially have dual mono on any mixer...

One of the problems with attempting simple summing is, that if you have different things from the same source (stereo) if you combine them wherever a source arrives 1/4 wave length apart cancellations occur...If you consider the shear number of frequencies and with the passage of time the mind boggling number of potential occurrences...you can see that that isn't something to be taken lightly...

These same principles also happen when mic sources are crowded together on stage, like on drums, but is no where near as bad as the summing risk.
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b_dann_b
Presonic
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Hi Gadget, didn't exactly realize that, but it does make logical sense.

So 1 simple scenario - guy hires the rig to do a band, pans the floor tom to the far left, 1st rack tom to the far right, 2nd tom to the middle (which is not that uncommon) ... my question around the summing would address this by forcing everything mono, where as if i just let it be, i'd prob get a phone call saying the rig isn't working (even though i told him to just the left output on his mixer and not pan at all).

how do people deal with subs without a dedicated drive rack or equiv (i know that they should be using this sort of device, but is this the case?). just left channel into amp?
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PvG
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Hey guys, to sum 2 symmetrical balanced channels into 1 symmetrical balanced input you don't need resistors! Use +/pin2 from one output and -/pin3 from the other and connect them to pin2 and pin3 resp of the input... Voila, a 2 channel mixer with fixed gain in a cable.
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TimmyP1955
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http://www.rane.com/note109.html
http://www.padrick.net/TP_Audio.htm
b_dann_b
Presonic
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TimmyP1955 wrote:http://www.rane.com/note109.html


its in my original post. problem is someone on another forum says that the diagram is slightly wrong. i dont know whether it is or not. was hoping someone could confirm.
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PvG
Presonic
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The circuit in the rane note will work fine, especially because you're summing line level signals from the same source (and not 2 mic level sources with long cables going different directions). The probability that you get interference is very little.

Because you're summing line level, you can even try it without resistors as I described in my post above.
www.plugingeluid.nl
If you can't do it like you should, you should do it like you can...

Amps: Stage Accompany 5x SA1600 + 2x SSA100, 3x Behringer DCX2496 processor,
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Mixer: Presonus SL24 + MacBook Pro + analog multi with 108p Harting,
Mics: Shure drumkit, SM58's, SM57's, AKG DMS70 wireless + some others.
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b_dann_b
Presonic
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cheers. got the resistors on order. will give it a crack.
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lowdbrent
Presonic
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PvG wrote:Hey guys, to sum 2 symmetrical balanced channels into 1 symmetrical balanced input you don't need resistors! Use +/pin2 from one output and -/pin3 from the other and connect them to pin2 and pin3 resp of the input... Voila, a 2 channel mixer with fixed gain in a cable.


Sorry, you do need the resistors. The Rane site is correct.

Edit. Oops. Did not read the end of the thread. OP, let us know how it goes.

This message was edited 1 time. Last update was at 29/08/2012 02:46:58

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b_dann_b
Presonic
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still waiting on resistors

but the point you made seems to be what everyone s debating about. as long as the rane resistor values are correct then hopefully all goes well.
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b_dann_b
Presonic
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thought i'd do a follow up on this seeings i think i've come to a compromise and also found some interesting things that i wouldn't have thought would make a difference.

so the setup i ran was with 2 ps10s and a sub either side setup in stereo.

So i put the left and right from mixer into the first controller. sent the left and sub out from controller into the first amp. took the right out from the controller and the left channel out from the amp (in theory this is a link type scenario) and sent them to the second controller where i then used the right out and the sub out (from the 2nd controller) to run the second amp. The reason i used the second controller is because i was testing this setup to reduce screwing around if the rig goes out in 2 pieces at hire time. Also i wanted to make sure both subs got that same summed signal.

I found doing it this way i actually had less volume on the right side. Odd, but i believe it was because the controller was double handling the channels where i thought that if one controller did what it needed, by the time the other controller gets the signal, it was already processed and the 2nd controller would have to do almost nothing - i was wrong and there was a considerable difference in the volume of each side.

Anyways i ended up just running the left signal to the left controller and the right signal to the right controller and didn't worry about the subs getting a summed signal and had dramatically better results.

just thought i'd share. i would prefer to have a summed signal to the subs, but thats the compromise.
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roly-m
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You sure are good at making things complicated.

Are you saying that you will rent your rig to someone who doesn't understand that it's a mono rig?
b_dann_b
Presonic
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tell me about. although it sounds complicated, from a cabling point of view for a renter it was easy (thats what i was testing) - left and right in, left and right out, left and right in. connect one rack to 1 set of speakers, connect the other rack to the other set of speakers.

whether the system goes out in in full, or half, the exact sames plugs/cables and no messy around to reconfigure every time. whilst i wouldnt like to send it out to someone who doesn't understand its a mono system, it may become inevitable.
Audio Engineer
Network Administrator - Win2003/2008 server, WinXP/7, Cisco, OSX, OSX Server

StudioLive 16.4.2
AudioBox 1818VSL
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