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Author Topic: Mixer summed mono voltage?  (Read 9513 times)

Ivan Beaver

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Re: Mixer summed mono voltage?
« Reply #10 on: August 04, 2014, 03:28:13 pm »

Thanks everybody.  The mixer is an Allen and Heath Xone 464, a better DJ mixer. 

John, if the summed mono is just for convenience and isn't calibrated, I don't want to use it. I have 4 Labhorns that I want to fully power and limit properly, and I'm trying to learn the science behind proper levels, xover, limiter, and amp settings. I was going to use the summed mono as a feed to the C input on a DCX2496, because I could control the level to the subs with a separate main fader ... the mixer has two main busses, either of which can be summed to a mono out.

I've started with trying to understand signal sources and mixer levels..

Ivan, I'm not sure what you mean by 'how much gain it has at that stage'...Its maximum output level is spec'd @+26dbu.
Tim, the same signal is going to both channels via a y cable. I've been using a 1kz +4dbu 1.23v sine wave.


Max output and gain are very different things.  You can reach max output with just a little gain or a lot-it depends on the previous stages and devices.

"Calibrated" can mean very different things to different people.  Calibrated to "what"?  You don't calibrate gain.  It is what it is.  You can calibrate some meters-but you also have to consider at what point the meter is reading.

Some mixers have level controls after the stage that the meters are looking at-others do not.  The good ones will show the actual output level.

The limiting is done AFTER the mixer and the mixer gain has nothing to do with the limiting of the amplifier outputs.  Those are separate discussions with different outcomes.

And before we go down the same rabbit hole-the level controls on the amplifier have NOTHING to do with the output power capability of the amplifer.

You can turn them just about all the way down and the amp can still put out full power.

Just heading it off before we go there. ;)
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Ivan Beaver
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Tim McCulloch

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Re: Mixer summed mono voltage?
« Reply #11 on: August 04, 2014, 04:42:16 pm »

Hi Tim, you called it...I'm the only operator.  This is pure personal hobby...many decades of it.
And yes, its easy enough to compensate for elsewhere.

For playing a mix of recorded music, I have found I like having two sliders next to each other, one for the mains and one for the subs.  I know this messes with the crossover region acoustically, but it sure is handy, especially for balancing out perceived  highs vs lows across wide volume swings.  Any overpowering reason not to ?

Thx, Mark

Just increase the level at the DSP input to make it match the L/R levels.  Your faders will then track together.
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Mark Wilkinson

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Re: Mixer summed mono voltage?
« Reply #12 on: August 04, 2014, 05:11:34 pm »

Just increase the level at the DSP input to make it match the L/R levels.  Your faders will then track together.

Yes, will do.  Just to learn, what should a summed mono voltage read, both stereo inputs with 1.23v?  Would it matter if the two input signals were identical?
Thanks again.
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John Roberts {JR}

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Re: Mixer summed mono voltage?
« Reply #13 on: August 04, 2014, 05:58:55 pm »

Yes, will do.  Just to learn, what should a summed mono voltage read, both stereo inputs with 1.23v?  Would it matter if the two input signals were identical?
Thanks again.

The "nominal" output on the mono XLR is supposed to be the same 1.23V (according to their user advice).

That said when you combine a real stereo signal to mono, the answer is not so clear-cut because the left and right signals are not coherent. Are you using stereo program material and expecting some stable precise mono output level? 

Without looking at their schematic I can not predict accurately. I am not aware of any hard rules for how to handle mono outputs in a stereo world. Mono feeds are generally provided for less critical applications.

Summing two identical mono signals on L & R might combine 2x or might be normalized so each adds with 1/2 weight to sum to 1x.

You are the man with the meter,,, you tell us. (Your 0.9V measurement does not appear to agree with any of my hypotheticals).

JR

PS:  BTW have you tried asking A & H ? They are generally pretty responsive to customer service issues.
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Patrick Tracy

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Re: Mixer summed mono voltage?
« Reply #14 on: August 04, 2014, 07:16:12 pm »

I'm getting about .9v from the summed mono output.

I may be off base here, but I'm wondering if it's an impedance balanced output and measuring hot to ground would be different from hot to cold.

Mark Wilkinson

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Re: Mixer summed mono voltage?
« Reply #15 on: August 04, 2014, 07:28:45 pm »

The "nominal" output on the mono XLR is supposed to be the same 1.23V (according to their user advice).

That said when you combine a real stereo signal to mono, the answer is not so clear-cut because the left and right signals are not coherent. Are you using stereo program material and expecting some stable precise mono output level? 

Without looking at their schematic I can not predict accurately. I am not aware of any hard rules for how to handle mono outputs in a stereo world. Mono feeds are generally provided for less critical applications.

Summing two identical mono signals on L & R might combine 2x or might be normalized so each adds with 1/2 weight to sum to 1x.

You are the man with the meter,,, you tell us. (Your 0.9V measurement does not appear to agree with any of my hypotheticals).

JR

PS:  BTW have you tried asking A & H ? They are generally pretty responsive to customer service issues.

Thanks John, yes the .9v doesn't seem to agree with anything.....
I'll ask A&H..

Patrick, the mono out has a balanced xlr and impedance balanced trs...I'll compare the two..

Ivan, no worries...had no intention of going down that rabbit hole !  I actually think I understand at least several of the issues in that hole :)  A lot of you guys posts, and stuff like Meyer's Sound Design Reference have helped.  Their Speaker Sense ECU for the non-powered stuff explains a lot.  Do you know of a reasonably priced limiter or speaker management device that monitors and controls actual amp voltage output, peak and rms?

And while I have you :) ..... and assuming my attachment makes it into this post (it doesn't preview for some reason)...
please look at these SPL readings I just took from 4 labhorns.   I measured each one individually, then 2, then 4.  Used sine waves at 2.0v, 4 meters. Measured unweighted with supposedly good meter.
Labhorns were next to my house, firing down the length of a 2nd floor deck.  So I don't really know what space to say they were in...probably something effectively a little less than 1/2 space.

Anyway, the way the dip at 62 hz on 1 and 2 boxes disappeared with 4 boxes blew my mind.  I went back and tried 3 boxes, and found the dip gone there too.  I remember Tom saying the design was for a minimum of 6 boxes...wow, now I wish I had two more.  I sure wont use less than 3 together...unless I find these measurements to be bogus.  Your thoughts?  Thx. Hope it was ok to change subject here...sorry if I should have made new post on Labhorn forum...
« Last Edit: August 04, 2014, 07:36:17 pm by Mark Wilkinson »
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Ivan Beaver

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Re: Mixer summed mono voltage?
« Reply #16 on: August 04, 2014, 07:54:11 pm »

Thanks John, yes the .9v doesn't seem to agree with anything.....
I'll ask A&H..

Patrick, the mono out has a balanced xlr and impedance balanced trs...I'll compare the two..

Ivan, no worries...had no intention of going down that rabbit hole !  I actually think I understand at least several of the issues in that hole :)  A lot of you guys posts, and stuff like Meyer's Sound Design Reference have helped.  Their Speaker Sense ECU for the non-powered stuff explains a lot.  Do you know of a reasonably priced limiter or speaker management device that monitors and controls actual amp voltage output, peak and rms?

And while I have you :) ..... and assuming my attachment makes it into this post (it doesn't preview for some reason)...
please look at these SPL readings I just took from 4 labhorns.   I measured each one individually, then 2, then 4.  Used sine waves at 2.0v, 4 meters. Measured unweighted with supposedly good meter.
Labhorns were next to my house, firing down the length of a 2nd floor deck.  So I don't really know what space to say they were in...probably something effectively a little less than 1/2 space.

Anyway, the way the dip at 62 hz on 1 and 2 boxes disappeared with 4 boxes blew my mind.  I went back and tried 3 boxes, and found the dip gone there too.  I remember Tom saying the design was for a minimum of 6 boxes...wow, now I wish I had two more.  I sure wont use less than 3 together...unless I find these measurements to be bogus.  Your thoughts?  Thx. Hope it was ok to change subject here...sorry if I should have made new post on Labhorn forum...
I am not aware of any stand alone limiter with monitoring-but that might be a good idea for a product.

Part of the problem trying to measure sub cabinets is that you REALLY have to far (think 50' at a minimum-depending on your measurement distance-speaker to mic) away from any reflective surface.

I see two problems with the way you were measuring the cabinets.  First you were close to your house (being on a deck) and second you were on a deck  on the second floor.

So you were getting cancelling reflections from both the house AND the ground.

Ideally you need to get in the middle of a large parking lot-but that is not always easy to do.

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Ivan Beaver
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Ivan Beaver

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Re: Mixer summed mono voltage?
« Reply #17 on: August 04, 2014, 08:23:22 pm »

Yes, will do.  Just to learn, what should a summed mono voltage read, both stereo inputs with 1.23v?  Would it matter if the two input signals were identical?
Thanks again.
There is no way to say what it "should" read.

Let's take a look at what is ACTUALLY going on in a mixer.

You cannot simply combine 2 signals/voltages.  Like with a Y cable.  Yes you can-but then the output stage of each stage will load down the output of the other stage-resulting in a lowered voltage and possibly damaging the output device due to driving a lower impedance than it is looking for.

So in a mixer-each signal goes through a series "summing resistor" and then they get combined into the next stage.

There is loss across these resistors.

Then the "makeup gain" stage provides gain to make up for the loss across the resistors-and maybe more.

So let's assume a meter that is placed after the summing resistors.  Let's say you read 1V with one channel (let's say the left) on.  When you add the same signal to the right channel the voltage will double or be 2V.  This is a 6dB gain (doubling of voltage-NOT adding 1 volt).  The difference between0.5 and 1 V is also 6dB.

So as you can see the gain of the summing amp can make a difference in what you are reading on the voltmeter.

And as JR said-if the signals are not the exact same-then there is no way to guess how much addition there will be.

I'm not sure if that helps or hurts any-but should give you something to think about.
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Mark Wilkinson

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Re: Mixer summed mono voltage?
« Reply #18 on: August 05, 2014, 09:46:44 am »

Thanks Ivan, I'm good with all the points you raised.  By what "should" the voltage read, I thought maybe there was some industry convention for final level after the summing resistors and "make up gain".


I just rechecked my measurements before asking A&H for help. With 1.23v out of each stereo output, the summed mono reads .94v for either the balanced +4 XLR or the impedance balanced -2 TRS.
.94v was the same whether sending a split mono 1kz sine through both channels, or sending a stereo signal ---- 1kz through left and 700hz through right.

If it's ok, I'm going to continue the labhorn discussion over in the labhorn forum...again, i apologize for switching topics...
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John Roberts {JR}

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Re: Mixer summed mono voltage?
« Reply #19 on: August 05, 2014, 10:33:28 am »

Thanks Ivan, I'm good with all the points you raised.  By what "should" the voltage read, I thought maybe there was some industry convention for final level after the summing resistors and "make up gain".


I just rechecked my measurements before asking A&H for help. With 1.23v out of each stereo output, the summed mono reads .94v for either the balanced +4 XLR or the impedance balanced -2 TRS.
This seems wrong, since there should be a 6dB difference between TRS output and XLR unless their user advice is incorrect.

Apparently mono output is post fader, and there is a rear panel selector switch to alternate between mix 1 or mix 2.

JR
Quote
.94v was the same whether sending a split mono 1kz sine through both channels, or sending a stereo signal ---- 1kz through left and 700hz through right.

If it's ok, I'm going to continue the labhorn discussion over in the labhorn forum...again, i apologize for switching topics...

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Re: Mixer summed mono voltage?
« Reply #19 on: August 05, 2014, 10:33:28 am »


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