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Author Topic: Vocals in separate PA  (Read 31897 times)

Dave Rat

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Re: Vocals in separate PA
« Reply #20 on: May 03, 2007, 08:49:39 pm »

Hello Hello

Ok, here is the run down on the concept, advantages and common usages of the concept of the dual PA implementation.

First of all, the big advantage of the dual system is that it reduces the negative effects of the inherent and significant inter-modulation distortion (IM Distortion) in speaker systems. As far as running two half ass 'ed PA's vs one full PA, I run two full PA systems side by side.

The concept is based on something that monitor engineers have been doing on the upper touring levels for many years which is using separate wedges for vocals and instruments. If you are curious as whether the dual PA concept works, it is quite simple to try it with wedges. The fact that the advantages can be experienced with monitor wedges also addresses the inaccurate comment(s) that the concept only applies on a large scale.

For those that are unfamiliar with IM distortion, one aspect of it can be looked at as follows: Speakers are most efficient when the voice coil is centered in the gap and least efficient when the cone is fully extended or fully pulled back. This efficiency drop which manifests itself as a non linearity I.E. distortion, can be both electrical and mechanical and can be quite significant. When one frequency put the cone or diaphragm in motion and another tone is introduced, the two frequencies effect the efficiency that the other is being reproduced causing distortion. The dual PA not only reduces the complexity of the signals driving each of the speaker system, it also allows more line array speakers to be used to cover a given space therefore allowing a reduced level to be sent each speaker reducing mechanical and thermal compression. Furthermore, it allows for improved sight lines by reducing the need for excessively long line array "banana's" in room with raised seating on the sides.

To demonstrate the effects at home of IM distortion, take two wedges and run a low frequency tone into both and then talk into a mic that is also running into both wedges, while the tone is on at fairy high level. Now rewire so that the tone comes from one wedge and the vocal comes from the other wedge and listen again. The difference in vocal clarity is should be readily audible and dramatic in 2-way monitors and becomes more and more significant as volume is increased.

I did extensive testing of this phenomenon while developing the MicroWedges and attempting to avoid this phenomenon was the basis for the three way Rat Sound L-Wedges developed in the mid 80's.

With a three way monitor where the vocal radiates from the mid and high speakers and the tone is in the low speaker, the difference is minimal. To demonstrate the reduced but still existing IM distortion issue with a three way monitor, the tone would need to be at the lower end of the midrange driver's frequency range.

As far as the reference to the Wall of sound, yes, that design was considered in the concept and I am striving for the same advantages they were so many years ago. The difference is that now with the proliferation of line arrays, the opportunity to have two PA's side by side is now a reality. Thus there is room to implement a tourable and realistic multi system setup within the existing accepted rock touring paradigm.

My original concept was to have three PA's. One for vocals, one for guitar and one for bass and drums spread between. I built small scale mock up of the system and using past tour multi track recordings I did some testing which indicated that the majority of the advantages were realized when going from one PA to two systems and adding the third was much less dramatic.

The beauty of the dual setup is that I can switch from mixing into a single PA to a mixing into dual PA in real time during a real concert. It is not like "OK, maybe it sounded better yesterday" It is "listen to this and now listen to this! Do you hear the difference?"

Regarding comments about interference between the dual PA systems, just as placing a bass rig on stage next to a guitar rig on stage causes no interference issues because they are reproducing different signals, having a vocal Pa next to an instrument PA also causes no interference issues as I never run the same signals into both systems.

As far as budgeting all that gear, well, that is a tough one and Peppers have been touring with this dual rig for over year now and I would have lost my budgeting for it long ago if the difference was not so clearly stunning and so easily demonstrate able.

Now that is all hardware I am talking about. As far as my mixing abilities and whether any particular show sounded good or not, well, that is a separate issue and have at it, but that is unrelated to the technical angle regarding the effectiveness of utilizing a dual system.

Also, to clarify, I run Bass/Guitar, Toms and Cymbals to the outside stereo clusters and Vocals/Kick and Snare to the inside stereo clusters.  The reasoning is that though the Kick and Snare will effect the vocals with some IM distortion, they are short burst signals so vocal intelligeablity wont be significantly diminished.  The bass is mainly reproduced by the 15"s and 2"s in the outer clusters where as the guitar is more prominant in the 7" speakers. The tom toms are infrequent enough that the negative effects their signal has is a non issue.

I saw some links to the blog I have been writing on about the tour, and there is more info there if you do a search for "Sound Nerd Speak"

OK, I hope that opens a big huge can of worms and opinions!!  I fully expect and have seen considerable resistance already from all but a few with open minds as of course I am clearly a bit of a crack pot for doing anything aside from the generic accepted ways of setting up PA's. For some strange reason a high percentage of sound humans seem to be dead set on doing their best to stick to the half a century old stereo paradigm while light systems now move and video has been created and sets designs come up with new and innovative contraptions, we sound people must stick to hanging a good old fashioned stereo PA, because, hey, that's the way it is done.

But what if?  What if it really does sound better? What if the dual setup truly does improve clarity and I am not crazy?  Hmmm, that would mean that the audience gets a better show, the bands gets better sound, the PA vendors get a bit more budget and we as sound engineers have more fun doing what we love to do. I must say I am having the most fun mixing that I have ever had in my 27 year career!!

Oh, and I also hope that credibility assigned to the opinions offered are directly proportional to the amount of testing and research that the opinionators have done to create up their stances.



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Evan Kirkendall

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Re: Vocals in separate PA
« Reply #21 on: May 03, 2007, 08:52:33 pm »

Holy shit!

Dave Rat's on PSW!!  Shocked  Shocked  Shocked


Dude, you gotta be bored to be here. Razz


Great post as always. I always enjoy reading your stuff!





Evan
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Too Tall (Curtis H. List)

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Re: Vocals in separate PA
« Reply #22 on: May 03, 2007, 10:29:44 pm »

Dave Rat wrote on Thu, 03 May 2007 20:49

Hello Hello

Ok, here is the run down on the concept, advantages and common usages of the concept of the dual PA implementation.

First of all, the big advantage of the dual system is that it reduces the negative effects of the inherent and significant inter-modulation distortion (IM Distortion) in speaker systems. As far as running two half ass 'ed PA's vs one full PA, I run two full PA systems side by side.

Snip-





Hi Dave,
Broadways have been doing this longer then I have been working IA gigs (late 70s).
They might have been doing it before The Dead used The Wall of Sound, but I don’t know that for sure.

Beyond IM distortion a separate speaker system can be deployed in different places to address the fact that the orchestra is in a different place and has a great deal more stage volume then vocals. The flexibility can be a huge advantage when you want to put more vocals in a dead spot you just point the vocal box over a bit without bringing more orchestra, which the spill from the pit is covering just fine.
Some of the people I have worked with that have been mixing plays for years are absolute masters at this. You have to give props to the sound designers too.

In what you are doing the vocals and “orchestra” are all in the same place so you don’t need the flexibility quite as much.

For IM distortion drivers/speaker design has come a long way. It has been a while since IM has been a “First order” problem. I measure IM on all the drivers and the final speaker with xover and it is very low as long as you stay away from the MI series driver or more to the point true “Guitar speakers”.
That said when you push drivers hard I would guess it gets worse.
If you hear an appreciable improvement in a live setting I applaud your effort. Compared to studio or high end Home Theater, Live Sound has always been more of a challenge to produce high quality sound (not that most of the Ipod MP3 users would notice through their $1.99 ear buds).
And in your case the SPL you are pushing makes every type of distortion more of a problem.
Cheers

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Vince Byrne

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Re: Vocals in separate PA
« Reply #23 on: May 04, 2007, 11:58:11 am »

Dave Rat wrote on Thu, 03 May 2007 19:49

I fully expect and have seen considerable resistance already from all but a few with open minds as of course I am clearly a bit of a crack pot for doing anything aside from the generic accepted ways of setting up PA's.

That's why they call it the "bleeding edge"...

The physics make sense. I can hear it with mons. I'll probably never be able to afford it with mains, but thanks for looking over the edge and sharing what you find there with us.

Peace,
Vince
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John Roberts {JR}

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Re: Vocals in separate PA
« Reply #24 on: May 04, 2007, 12:53:39 pm »

I find sound reproduction and reinforcement critically flawed from the start so there's many flaws to attack and perhaps master. Even a perfect speaker will have Doppler distortion from combined sources in the same passband. To some lesser extent there's probably IM in free space too. Trying to squeeze everything into one speaker system is probably expecting too much from the best technology.

I have given this some thought on a smaller scale for hifi reproduction. A dedicated vocal, drum/bass, and lead channel with dedicated and spatially located speaker systems could get us one step closer to that live band playing in our living room. For sound reinforcement what is the true goal? A live band 25' away from everybody in the audience, or one 50' tall kick drum on stage?  Perhaps a little of both.

Live sound reinforcement often crosses the line and creates something more than just what's on stage. That's good if it good. Anybody who's ever done micro-SR where you just throw the vocals through a few plastic speakers on sticks knows that you can get some damn good sound by keeping all the sources discrete. Scaling this up to mega-SR surely has merit for those with the budget and capable of dealing with the logistics.

JR    
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Scott Van Den Elzen

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Re: Vocals in separate PA
« Reply #25 on: May 04, 2007, 08:21:02 pm »

Evan Kirkendall wrote on Thu, 03 May 2007 17:52

Holy shit!

Dave Rat's on PSW!!  Shocked  Shocked  Shocked


Dude, you gotta be bored to be here. Razz


Great post as always. I always enjoy reading your stuff!





Evan


I'll second that!  

Dave, I can't tell you how cool it is that you chimed in on this thread!  You've given me tons to think about, as is the case anytime I read what you write.
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Scott Van Den Elzen

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Re: Vocals in separate PA
« Reply #26 on: May 04, 2007, 08:22:45 pm »

Vince Byrne wrote on Fri, 04 May 2007 08:58

Dave Rat wrote on Thu, 03 May 2007 19:49

I fully expect and have seen considerable resistance already from all but a few with open minds as of course I am clearly a bit of a crack pot for doing anything aside from the generic accepted ways of setting up PA's.

That's why they call it the "bleeding edge"...

The physics make sense. I can hear it with mons. I'll probably never be able to afford it with mains, but thanks for looking over the edge and sharing what you find there with us.

Peace,
Vince


A few comments are implying this is only meaningful on big rigs, or arrays.  Why wouldn't I want to do this with my little 250 person rig?  Will we all be doing it soon just like Aux Fed subs??

It seems like a relatively small thing -- what do I need?  1 more snake send from a sub group, a crossover (or not, depending on the system.)  A couple amp channels, and two more top boxes (that I already have just sitting in the trailer for most gigs anyway.)

I'm definitely going to experiment.  If it works as well as I think it may, it could noticably improve my sound.  Seems like that might get me more business at better prices, making the extra rig and labor pay for itself, and enabling the business to expand.  

No harm in trying.
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Bob Leonard

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Re: Vocals in separate PA
« Reply #27 on: May 04, 2007, 08:30:49 pm »

John Roberts  {JR} wrote on Fri, 04 May 2007 12:53

I find sound reproduction and reinforcement critically flawed from the start so there's many flaws to attack and perhaps master. Even a perfect speaker will have Doppler distortion from combined sources in the same passband. To some lesser extent there's probably IM in free space too. Trying to squeeze everything into one speaker system is probably expecting too much from the best technology.

I have given this some thought on a smaller scale for hifi reproduction. A dedicated vocal, drum/bass, and lead channel with dedicated and spatially located speaker systems could get us one step closer to that live band playing in our living room. For sound reinforcement what is the true goal? A live band 25' away from everybody in the audience, or one 50' tall kick drum on stage?  Perhaps a little of both.

Live sound reinforcement often crosses the line and creates something more than just what's on stage. That's good if it good. Anybody who's ever done micro-SR where you just throw the vocals through a few plastic speakers on sticks knows that you can get some damn good sound by keeping all the sources discrete. Scaling this up to mega-SR surely has merit for those with the budget and capable of dealing with the logistics.

JR    


JR,
I have used this technique on a very small scale for about 12 years now. I've said many times that I suppliment my backline using MIDI systems from Roland to the tune of about 10K. The realism is dependent on the audio chain used to reproduce the MIDI samples, those being bass, drums, horns, violins, piano, you name it and depending on if I have a bass player or drummer in for the gig. So I run seperate audio chains for vocals, monitors and all backline instrumentation. The instrumentation audio chain ends up coming through BUS 1/2 into SRX 725s and a pair of 18" subs. Vocals are through the same board but through the main mix, a seperate audio chain and eventually into the speakers used for FOH. Depending on the gig that could be another pair of 725s, EV SX500+, TA15s or combo in some cases, and without subs for vocals. Lately, after a job request a few months ago, I have been placing everything BEHIND the band (wall of sound). I am totally blown away by the quality of the sound overall. There is no interaction between the systems and everything is distinctive and clear even when I hit the dance floor 40-50 feet away at 90-100Db. Does it get load on stage?? Sometimes, but never loader than the vocals. The biggest advantage is the near perfect mix the audience hears. Smile



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Dan Brandesky

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Re: Vocals in separate PA
« Reply #28 on: May 04, 2007, 08:47:06 pm »

I love this concept and think it's great, but I'm curious as to what to do if you had to set up a dual PA for a large, outdoor event. Think maybe a 4th of july festival in a large park; there is no defined audience area, so the object is to get as much sound to the front and sides of the stage as possible. How would a dual PA best be implemented in that kind of setup?

-Dan
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Dave Rat

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Re: Vocals in separate PA
« Reply #29 on: May 05, 2007, 12:28:05 am »

THe dual PA works exactly the same as a conventional system coverage wise if you keep the sytems close together.  I just used the dual setup for Coachella Festival's main stage last weekend with the Peppers and was quite happy, all good!
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