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Splitting signal to run into both channels of a powered speaker to get more output...


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is that even a thing? I played with a band this past weekend that did this, and it doesn't seem to make any sense to me, but I was wondering why they might have done it. They split the signal from the mixer to two XLRs on each side and then ran both into channels 1 and 2 of the mixer of the EV ZLX-15P main. "To get more output" they said.

 

Does it make any sense to do this? Why not run just one XLR to the first channel and then crank the preamp to get more output?

 

If anyone can help me understand this sort of behavior, I'd appreciate it.

Brian

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Sounds like they are running the mixer mono by doing that instead of stereo. You'd be driving the cabs with the left and right sides of the mixer combined, and it may actually be louder depending on the mixers panning laws. There's an easier way of doing this instead of running two cables to the cabs. You simply, combine the left and right channels at the board then split the mono signal and run two single cables to the cabs.

 

Neither of these ways is advisable however. When you combine the line outs on a mixer and run them in parallel there's nothing stopping the signal coming out of the left channel and feeding back into the right channel or vice versa.

 

If you had a channel panned right it would feed back into the left channel just as much as it would feed into the right in the wrong direction just as much as it would the cable to feed the speakers. The signal is mooned at the pan pot where its supposed to be. You shouldn't parallel the line output amps directly like that or it could cause circuit damage.

 

If they aren't getting enough signal strength the best solution would be to get a line preamp or compressor unit to boost the signal. Some mixers do have low outputs so I'm not surprised they are combine both to get a stronger signal, but they need to do it the right way to avoid problems.

You can also use a DI box designed to combine stereo to mono signals actively. The signals need to be buffered to prevent the signals from feeding back into the mixers line outputs.

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Sounds to me like someone knows the old guitarist trick of running the guitar signal into both channels on a Fender tube amp to utilize both pre-amps and get a volume boost and assumed this would translate to a modern speaker.

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That would be an amazing extra 3 db. (Assuming they are actually in phase.) Most systems have some built in headroom that would result in exactly the same level when things begin distorting.

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Sounds like they are running the mixer mono by doing that instead of stereo. You'd be driving the cabs with the left and right sides of the mixer combined, and it may actually be louder depending on the mixers panning laws. There's an easier way of doing this instead of running two cables to the cabs. You simply, combine the left and right channels at the board then split the mono signal and run two single cables to the cabs. Neither of these ways is advisable however. When you combine the line outs on a mixer and run them in parallel there's nothing stopping the signal coming out of the left channel and feeding back into the right channel or vice versa. If you had a channel panned right it would feed back into the left channel just as much as it would feed into the right in the wrong direction just as much as it would the cable to feed the speakers. The signal is mooned at the pan pot where its supposed to be. You shouldn't parallel the line output amps directly like that or it could cause circuit damage. If they aren't getting enough signal strength the best solution would be to get a line preamp or compressor unit to boost the signal. Some mixers do have low outputs so I'm not surprised they are combine both to get a stronger signal, but they need to do it the right way to avoid problems. You can also use a DI box designed to combine stereo to mono signals actively. The signals need to be buffered to prevent the signals from feeding back into the mixers line outputs.
Huh? If I'm not mistaken they are in stereo, just using both inputs on each cab, thinking its louder.
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Sounds to me like someone knows the old guitarist trick of running the guitar signal into both channels on a Fender tube amp to utilize both pre-amps and get a volume boost and assumed this would translate to a modern speaker.
Lest anyone gets the wrong idea ... This would increase the "drive" but not the maximum output. The max output of anything is what it is. How hard you have to get there is a different issue.
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Huh? If I'm not mistaken they are in stereo, just using both inputs on each cab, thinking its louder.

 

If that's the case, the second jack on the cabs is simply an parallel link output to connect additional powered cabs. Its not going to hurt anything.

Running two cables in parallel would only make a difference unless they have horribly bad cords and the pair running in parallel might increase the continuity.

 

Many mixers cheat XLR connectors and what might be happening is the line level signal coming from the mixer may not be a true balanced low impedance send. It may be a high impedance unbalanced signal connected to the mixers XLR ground and hot wire output. (essentially a Hi Z Output) If this is the case the signal might decay over a long run of 50~100'. Doubling the continuity may lessen the attenuation of an unbalanced signal.

 

If I knew what mixer was used I could likely find a schematic and specs to be sure. Cheap mixers often use unbalanced high impedance connections inside the mixer on both the XLR inputs and power amp outputs. They simply use stronger preamps to overcome the cable losses.

 

I am trusting they actually do hear a difference in this case and giving some explanation vs. just blowing them off as being idiots as many seem to have done here. It could just as easily be they "think" the powered cabs jacks are like dual channel guitar amps, but in this case the jacks have no difference. They are simple parallel connections according to the specs just like a normal speaker cab has an extra parallel plug so you can link other cabs.

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That would be an amazing extra 3 db. (Assuming they are actually in phase.) Most systems have some built in headroom that would result in exactly the same level when things begin distorting.

 

Doubling the voltage is actually give you a 6 dB boost, but who is counting... This is reminiscent of the old "double-busing" thing people used to do (and some still swear by) in the mixing world. Anyone who has ever tried to argue why this doesn't matter (and can be problematic) knows how hard it is to educate people out of their ignorance.

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Yea, there is not a whole unused power stage waiting to be utilized. ...same pair of 6v6 or 6l6 tubes for whatever comes before it!

 

Exactly!

 

This is often a mistake that the uninformed make when testing gear at a music store. They plug into two say 500W amps and say one is louder than the other because at zero on the board one does sound louder. But once you adjust the drive level they are the same, which is what you would expect from two amps with the same power.

 

Same goes for those that think if they turn down the sensitivity control on their power amp that their power goes down ... which it certainly does not. "Hey, if I turn the knob halfway down I'll get half the power". Well you will "hear" a drop in level but you will not restrict the maximum output of the power amp. It remains constant ... 6v6's or not ;)

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If that's the case, the second jack on the cabs is simply an parallel link output to connect additional powered cabs. Its not going to hurt anything.

Running two cables in parallel would only make a difference unless they have horribly bad cords and the pair running in parallel might increase the continuity.

 

Many mixers cheat XLR connectors and what might be happening is the line level signal coming from the mixer may not be a true balanced low impedance send. It may be a high impedance unbalanced signal connected to the mixers XLR ground and hot wire output. (essentially a Hi Z Output) If this is the case the signal might decay over a long run of 50~100'. Doubling the continuity may lessen the attenuation of an unbalanced signal.

 

If I knew what mixer was used I could likely find a schematic and specs to be sure. Cheap mixers often use unbalanced high impedance connections inside the mixer on both the XLR inputs and power amp outputs. They simply use stronger preamps to overcome the cable losses.

 

I am trusting they actually do hear a difference in this case and giving some explanation vs. just blowing them off as being idiots as many seem to have done here. It could just as easily be they "think" the powered cabs jacks are like dual channel guitar amps, but in this case the jacks have no difference. They are simple parallel connections according to the specs just like a normal speaker cab has an extra parallel plug so you can link other cabs.

 

sort of but not really.

 

many Active PA cabs have two distinct channels with a gain control. One power module though. QSC. EV, Yamaha, EON, PRX all have two channels. Yes, they do have an XLR pass thru but that would obviously be on an XLRm. An XLRf is not a thru.

 

I don't know about your "cheat" high impedence on XLR outputs. I think the mixer itself has little to do with the issue stated by the OP. The end user thinks that the two volume controls are adding up to more volume, which they probably are, but they are simply mixing the same signal into the same power amp...for no practical reason. They may not be idiots but misinformed. At minimum they've added extra kludge, cost and failure points. If it was sold to them by a retail store, the salesperson would indeed be an idiot.

 

 

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Many mixers cheat XLR connectors and what might be happening is the line level signal coming from the mixer may not be a true balanced low impedance send. It may be a high impedance unbalanced signal connected to the mixers XLR ground and hot wire output. (essentially a Hi Z Output) If this is the case the signal might decay over a long run of 50~100'. Doubling the continuity may lessen the attenuation of an unbalanced signal. If I knew what mixer was used I could likely find a schematic and specs to be sure. Cheap mixers often use unbalanced high impedance connections inside the mixer on both the XLR inputs and power amp outputs. They simply use stronger preamps to overcome the cable losses. I am trusting they actually do hear a difference in this case and giving some explanation vs. just blowing them off as being idiots as many seem to have done here. It could just as easily be they "think" the powered cabs jacks are like dual channel guitar amps, but in this case the jacks have no difference. They are simple parallel connections according to the specs just like a normal speaker cab has an extra parallel plug so you can link other cabs.
Your mixer comments are almost 100% inaccurate and/or false. 1. An unbalanced connection (hot and ground) is not and has nothing to do with high impedance. High impedance can be balanced or unbalanced. So can low impedance. 2. I can't think of any mixer that has been sold in this industry in the last 20 years that does not have sufficient drive capability to drive well above +4dBu. 3. An unbalanced signal feeding an XLR at line level can be impedance compensated to provide all of the benefits of a balanced connection other than a reduction of maximum drive level of 6dB. This can still deliver +18dBu rather than +24dBu, plenty of drive.
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I'm doing something kind of the same as the original poster but its not for volume. In my practice room I have a ZLX15p and a ZXA1 powered sub. I run both the left and right sends from the mixer to the inputs on the ZLX15 then the output on the zlx goes to the sub. I'm doing this so when I play something through and MP3 player it all goes to the one cabinet. I noticed that there was no guitar or other instruments on older van halen or ac/dc or beatles tunes because of the panning done on the original mixing. Does that make sense?

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That's OK....sometimes sound guys who should know what they are doing say/do things that confound me.

 

Case in point:

 

A few weeks ago we take a couple of powered speakers in for repair to a local, semi-retired guy who has done electronic work for us for years. Guy knows his stuff for the most part, and the speakers work great since we got them back. But he tells the guy in my band who picked them up (who doesn't know much about such things anyway) that "these powered speakers always need to be used in pairs."

 

I'm like "what? that doesn't make any sense to me. Maybe he was just recommending we always use more than one so we reduce the strain being put on one speaker...?" My guy says "no, that's not what he was saying. He saying to always use them in pairs."

 

So I try to explain to him that unlike a passive speaker run in series, an active speaker would have no way of knowing whether it was being paired up with another speaker on a stereo or split-mono signal. That no one (usually) is going to run two active speakers for every monitor send. That there must of been some sort of mis-communication between the two of them here?

 

Or maybe there's something that I still need to learn about such things? (Always a definite possibility, of course....)

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I'm doing something kind of the same as the original poster but its not for volume. In my practice room I have a ZLX15p and a ZXA1 powered sub. I run both the left and right sends from the mixer to the inputs on the ZLX15 then the output on the zlx goes to the sub. I'm doing this so when I play something through and MP3 player it all goes to the one cabinet. I noticed that there was no guitar or other instruments on older van halen or ac/dc or beatles tunes because of the panning done on the original mixing. Does that make sense?

 

you're using the speaker's "mixer board" to mix L & R...totally fine

of course you can do that at the mixer too..and send only one XLR

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you're using the speaker's "mixer board" to mix L & R...totally fine

of course you can do that at the mixer too..and send only one XLR

 

I'm using a yamaha mixer that has an input called 2TR or something like that. It runs in stereo and there is no panning on it. I could run the MP3 player into one of the stereo pairs and fix it that way but I couldn't see the harm in what I was doing.

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I'm using a yamaha mixer that has an input called 2TR or something like that. It runs in stereo and there is no panning on it. I could run the MP3 player into one of the stereo pairs and fix it that way but I couldn't see the harm in what I was doing.

 

Or use a proper summing cable on your MP3 player into a mono input.

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