ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 [All]   Go Down

Author Topic: passive stereo summing  (Read 7088 times)

Gary Fitzpatrick

  • Full Member
  • ***
  • Offline Offline
  • Posts: 130
  • Fermanagh, Ireland
passive stereo summing
« on: November 27, 2013, 08:16:29 pm »

I install quite a few CD players and Ipod connections into the churches which I service. The system is run in mono (100v line outputs), so there is no real point in eating two inputs on the soundweb for a stereo source. Now I know you can get away with simply connecting the left and right signal wires together and summing that way, but its not ideal or "correct".

If i put a 1k resistor on the left and right channels, and then joint the two resistors together, and splice together the grounds would this be an accepted solution?

Thanks
Logged
Allen Heath GL2000, EV sx300 over Community pro Subs, EV s-200 monitors, Zeck amplification

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3320
  • Isle of Wight - England
Re: passive stereo summing
« Reply #1 on: November 27, 2013, 08:51:50 pm »

I usually use 10K or 47K for this.


Steve.
Logged

Jim Thorn

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 64
  • State College, PA
Re: passive stereo summing
« Reply #2 on: November 27, 2013, 11:39:57 pm »

Gary,

I have worked on many systems specified by big-name consultants using 1k ohm resistors for summing--it seems to be a pretty standard practice.  Although you can usually get away with shorting left and right outputs together, you will alwayshave success using summing resistors instead.  I wish more installers would realize that!

Jim Thorn

 
I install quite a few CD players and Ipod connections into the churches which I service. The system is run in mono (100v line outputs), so there is no real point in eating two inputs on the soundweb for a stereo source. Now I know you can get away with simply connecting the left and right signal wires together and summing that way, but its not ideal or "correct".

If i put a 1k resistor on the left and right channels, and then joint the two resistors together, and splice together the grounds would this be an accepted solution?

Thanks
Logged

Ryan C. Davis

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 281
  • SL,UT
Re: passive stereo summing
« Reply #3 on: November 28, 2013, 12:01:14 am »

just curious about what this actually does to the audio signal? attenuates both channels (L+R) so when they sum the level will be more appropriate at the mixer? I've never heard any audible distortion or overdriven signals when using a y chord but I'm all about doing things the right way so I'm all ears.
Logged
Ryan Davis

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3320
  • Isle of Wight - England
Re: passive stereo summing
« Reply #4 on: November 28, 2013, 04:18:51 am »

If you don't use resistors, then any time the two outputs are not the same, current will flow between them.

The resistors limit this current so the outputs are not fighting each other and you end up with a signal which is a combination of the two. 

Any attenuation is dependent on the value of the resistors used and the input impedance of the circuit you are connecting to.

The resistor value is not critical and it usually works without resistors as the voltages and current are very low and will not cause damage.

However, if you think about in in terms of connecting two power amps to one speaker - you definitely wouldn't do that!


Steve.
Logged

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 9045
  • Atlanta GA
Re: passive stereo summing
« Reply #5 on: November 28, 2013, 09:04:46 am »

Horizon makes a neat little device that passively sums stereo outputs and has a transformer so it provides a single balanced output.

It even has a level control-which can be good or bad-depending.

Sorry I don't know the model number off the top of my head.
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Jeff Carter

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 363
  • Kitchener, ON, Canada
Re: passive stereo summing
« Reply #6 on: November 28, 2013, 09:17:43 am »

Whirlwind also makes the PodDI which sounds similar to the Horizon device. Mike Sokol mentioned it in a recent PSW Study Hall post.

A couple of Mike's recent posts deal with this subject. Have a look at his work here:

http://www.prosoundweb.com/tags/tag/mike+sokol
Logged
Mothers, don't let your babies grow up to be physics PhDs

Kevin Graf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 329
Re: passive stereo summing
« Reply #7 on: November 28, 2013, 09:47:13 am »

See:

RaneNote
"Why Not Wye?"
Dennis Bohn, Rane Corporation
RaneNote 109 written 1991; last revised 4/04


    Splitting Signals
    Subwoofing in Mono
    Unbalanced Summing
    Balanced Summing
    Output Impedances

Introduction

Wye-connectors (or "Y"-connectors, if you prefer) should never have been created.

Anything that can be hooked-up wrong, will be. You-know-who said that, and she was right. A wye-connector used to split a signal into two lines is being used properly; a wye-connector used to mix two signals into one is being abused and may even damage the equipment involved.

Here is the rule: Outputs are low impedance and must only be connected to high impedance inputs -- never, never tie two outputs directly together -- never. If you do, then each output tries to drive the very low impedance of the other, forcing both outputs into current-limit and possible damage. As a minimum, severe signal loss results.
more at:
http://www.rane.com/note109.html
Logged
Speedskater

Tommy Peel

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1462
  • Longview, Texas
Re: passive stereo summing
« Reply #8 on: November 28, 2013, 01:28:47 pm »

Horizon makes a neat little device that passively sums stereo outputs and has a transformer so it provides a single balanced output.

It even has a level control-which can be good or bad-depending.

Sorry I don't know the model number off the top of my head.

Were you talking about one of these?



Sent from my Nexus 4 using Tapatalk

Logged

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3320
  • Isle of Wight - England
Re: passive stereo summing
« Reply #9 on: November 28, 2013, 01:41:01 pm »

My first venture into live sound was with three Peavey XR600s with summing leads taking all three master outputs into the graphic in of two amps and all three monitor outputs going to the graphic in of the third amp.  One amp per side FOH and one for monitors. All summed with 10K resistors.

Did quite a few bands with this setup until we bought a desk!


Steve.
Logged

Patrick Tracy

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 513
  • Boulder, CO, USA
    • Boulder Sound Guy
Re: passive stereo summing
« Reply #10 on: November 28, 2013, 02:13:53 pm »

Wye-connectors (or "Y"-connectors, if you prefer) should never have been created.

So nobody should be allowed to split signals? Because of a small chance for bad sound or damage to some inanimate object?

I have all manner of Y-cables and they never get misused because they're mine and I know better. How is that a problem?

Thad Kraus

  • Newbie
  • *
  • Offline Offline
  • Posts: 16
Re: passive stereo summing
« Reply #11 on: December 05, 2013, 12:16:44 pm »

I use a Radio Design Labs TX-J2 quite often. Most likely is built the same or similar internally.
Logged

Kevin Graf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 329
Re: passive stereo summing
« Reply #12 on: December 05, 2013, 12:45:59 pm »

So nobody should be allowed to split signals? Because of a small chance for bad sound or damage to some inanimate object?

I have all manner of Y-cables and they never get misused because they're mine and I know better. How is that a problem?

But 'Dennis Bohn, Rane Corporation' wrote that, not me.
Logged
Speedskater

Mark Cadwallader

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1333
  • Helena, Montana USA
Re: passive stereo summing
« Reply #13 on: January 09, 2014, 05:47:32 pm »

So nobody should be allowed to split signals? Because of a small chance for bad sound or damage to some inanimate object?

I have all manner of Y-cables and they never get misused because they're mine and I know better. How is that a problem?

As cited in the Rane article, it is OK to use a "Y" cable to split a signal, but not to combine a signal. Mark C.
Logged
"Good tools are expensive, but cheap tools are damned expensive."

ProSoundWeb Community

Re: passive stereo summing
« Reply #13 on: January 09, 2014, 05:47:32 pm »


Pages: 1 2 [All]   Go Up
 



Page created in 0.053 seconds with 23 queries.