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Author Topic: How do you calculate PA size?  (Read 13809 times)

g'bye, Dick Rees

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Re: How do you calculate PA size?
« Reply #10 on: August 08, 2014, 08:03:17 PM »

I suspect that the seemingly "inflated" SPL spec may in fact be asking for a system with enough headroom so that hitting, say, 110dBc at FOH will not be running the system flat out...requiring the BE's to "mix down" on a marginal system on the edge of component failure.

I have assisted several local festivals in getting established, going through the various stages of SOS, trap cabs on scaffold, dual PA, etc until they got big enough (and experienced enough) to see the value in hiring an outfit with enough rig for the gig. 

Now they get "thicker" sound and happier band engineers who no longer have to pull out all the stops just to get close to the levels they need.
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Charlie Zureki

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Re: How do you calculate PA size?
« Reply #11 on: August 08, 2014, 09:37:48 PM »

I suspect that the seemingly "inflated" SPL spec may in fact be asking for a system with enough headroom so that hitting, say, 110dBc at FOH will not be running the system flat out...requiring the BE's to "mix down" on a marginal system on the edge of component failure.

I have assisted several local festivals in getting established, going through the various stages of SOS, trap cabs on scaffold, dual PA, etc until they got big enough (and experienced enough) to see the value in hiring an outfit with enough rig for the gig. 

Now they get "thicker" sound and happier band engineers who no longer have to pull out all the stops just to get close to the levels they need.


   +1


  Hammer
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g'bye, Dick Rees

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Re: How do you calculate PA size?
« Reply #12 on: August 08, 2014, 10:08:27 PM »

Hi, Charlie.  Hope all's well.

DR
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Robert Piascik

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Re: How do you calculate PA size?
« Reply #13 on: August 08, 2014, 10:45:23 PM »

Was the required 118dB A weighted, C weighted or flat?  Slow or fast response?

Of course this info wasn't specified, so we all know this is not specific enough to be useful. Dick had a good point in that it just may mean that they don't want 110dB to be straining the system (just as spec-ing a 40 ch console when there are only 22 inputs is designed to keep out the bottom feeders).

The venue is a county fairgrounds grandstand 250' wide but only 100' deep with the stage on the track right up against the fence so audience will need nearly 180 degrees coverage. I can't imagine that we would place FOH at 80'-100' from the stage given those dimensions. Music is a Southern rock band you have heard of.

My initial idea was to fly DSL SH46 two per side facing front with two SM80 per side (also flown) for side fills because that's what's readily available, but have no idea if that will be:
1) plenty
2) enough
3) not enough
4) not even close

Eight Danley TH-118 subs, everything powered by iT8K one box per ch

You can all chime in on why this is a good or bad idea, and for the size events I usually do that seems like a screaming PA, but in a theoretical sense how would you know what is 'big enough' and what is not?

I come to this forum to learn from guys that are waaaay smarter and more experienced at this stuff than me. Thanks in advance for any advice you can offer.

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Rick Powell

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Re: How do you calculate PA size?
« Reply #14 on: August 09, 2014, 05:32:14 AM »

Of course this info wasn't specified, so we all know this is not specific enough to be useful. Dick had a good point in that it just may mean that they don't want 110dB to be straining the system (just as spec-ing a 40 ch console when there are only 22 inputs is designed to keep out the bottom feeders).

The venue is a county fairgrounds grandstand 250' wide but only 100' deep with the stage on the track right up against the fence so audience will need nearly 180 degrees coverage. I can't imagine that we would place FOH at 80'-100' from the stage given those dimensions. Music is a Southern rock band you have heard of.

My initial idea was to fly DSL SH46 two per side facing front with two SM80 per side (also flown) for side fills because that's what's readily available, but have no idea if that will be:
1) plenty
2) enough
3) not enough
4) not even close

Eight Danley TH-118 subs, everything powered by iT8K one box per ch

You can all chime in on why this is a good or bad idea, and for the size events I usually do that seems like a screaming PA, but in a theoretical sense how would you know what is 'big enough' and what is not?

I come to this forum to learn from guys that are waaaay smarter and more experienced at this stuff than me. Thanks in advance for any advice you can offer.

You should be able to hit 108-110 dB easily at 100 feet from the stage with that system, provided the tops also have about 2k watts per speaker available.  Coverage wise, the SH series drop off pretty sharply outside their pattern, so I don't see you having 180 "true" degrees of inside the pattern coverage.  Using the SM80s for front fill might allow you to splay the 46s a little to the outside, so you may get acceptable coverage for most of your audience.
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Jonathan Betts

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Re: How do you calculate PA size?
« Reply #15 on: August 09, 2014, 09:52:05 AM »

FWIW, I have been running 4 TH 118/ 2 SM 80. Testing with a Radio Shack meter for soundchecks,  I can  hit 110dbc slow response at 80' with about 10db of headroom.

This sounds like a killer setup. Let us know how it goes!
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Ivan Beaver

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Re: How do you calculate PA size?
« Reply #16 on: August 09, 2014, 10:49:14 AM »

.

The venue is a county fairgrounds grandstand 250' wide but only 100' deep with the stage on the track right up against the fence so audience will need nearly 180 degrees coverage. I can't imagine that we would place FOH at 80'-100' from the stage given those dimensions. Music is a Southern rock band you have heard of.

My initial idea was to fly DSL SH46 two per side facing front with two SM80 per side (also flown) for side fills because that's what's readily available, but have no idea if that will be:
1) plenty
2) enough
3) not enough
4) not even close

Eight Danley TH-118 subs, everything powered by iT8K one box per ch

You can all chime in on why this is a good or bad idea, and for the size events I usually do that seems like a screaming PA, but in a theoretical sense how would you know what is 'big enough' and what is not?

I come to this forum to learn from guys that are waaaay smarter and more experienced at this stuff than me. Thanks in advance for any advice you can offer.

As stated earlier-the first step would be to do a model.  So if you use the Danley DIRECT-a free program for PC and MAC
  http://www.danleysoundlabs.com/support/ddt-files/

you could end up with something like below.  This is assuming the speakers are 40' apart with the SH46s flown at 20' and pointed towards the outside corners.

The SM80s are pointed inwards.  The TH118s are stacked in a block of 4 under each speaker system.  Of course a different sub configuration could be used.

I choose this layout to give the most even coverage. If you wanted the most SPL in the middle you could aim the SH46s inwards and have the SM80s towards the outside.  It depends on what is most important to you.

Some of the mic colors are as follows.  The RED is FOH ( I put it 80' out in the middle.)

The LIGHT BLUE is in the middle 20' from the stage and the green is in a far outside corner.

The other mics are kinda inbetween those locations.  You can add a lot more if you wish-but this is just a starting point.

I also did not spend any real time aiming or aligning the speakers-they are just put in and playing.  So the response could be a bit better if time was spent in that area.

But it gives a good indicator of what sort of PEAK SPLs and freq response you would be looking at.
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Roland Clarke

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Re: How do you calculate PA size?
« Reply #17 on: August 09, 2014, 06:27:33 PM »

Not in the real world. 

Maybe at some freq and the right position-but certainly not at a wide range of freq and at different points in the array.

That is just another "myth" that the marketing departments like.

In more detailed terms when you start looking at lobbing and cancellations, yes, but all systems, even trap boxes suffer from this.  I understand that your boxes avoid these problems because of their "unique" design, but then you are falling off at a standard 6db per doubling and as discussed in the other thread, whilst possible an ideal situation in an install where the system can be uniquely tailored to the room, more often than not, the rigors of touring or single hit dates doesn't allow this level of customisation and jobs have to be worked out using what is "on the trucks".

I'm not the greatest fan of line array's for all the reasons you have mentioned here and on other thread's, however, possibly their best attribute is the ability to cover fairly deep venues with a pretty good average SPL.  Forgetting the comb filtering aspect, close to 3-4db per doubling is achievable when measured on a A weighted leq 15 reading.  How good you or anyone else feel's it sounds is another subjective matter.

All this being said, as you pointed out, it depends on so many other factors, many of which have nothing to do with delivering the best sound solution.
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Ivan Beaver

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Re: How do you calculate PA size?
« Reply #18 on: August 09, 2014, 07:15:19 PM »

In more detailed terms when you start looking at lobbing and cancellations, yes, but all systems, even trap boxes suffer from this.  I understand that your boxes avoid these problems because of their "unique" design, but then you are falling off at a standard 6db per doubling and as discussed in the other thread, whilst possible an ideal situation in an install where the system can be uniquely tailored to the room, more often than not, the rigors of touring or single hit dates doesn't allow this level of customisation and jobs have to be worked out using what is "on the trucks".

I'm not the greatest fan of line array's for all the reasons you have mentioned here and on other thread's, however, possibly their best attribute is the ability to cover fairly deep venues with a pretty good average SPL.  Forgetting the comb filtering aspect, close to 3-4db per doubling is achievable when measured on a A weighted leq 15 reading.  How good you or anyone else feel's it sounds is another subjective matter.

All this being said, as you pointed out, it depends on so many other factors, many of which have nothing to do with delivering the best sound solution.
One of the big 'misunderstandings" is that "non line array" systems cannot deliver even freq/SPL front to back.

It is not hard at all-it just takes proper knowledge and design.

I have done many hundreds of systems that it is the same level at the front as it is at the back-WITH the same freq response!!!!!

Simply measuring with a SPL meter is pretty worthless in terms of saying it is the same SPL.

It gives "a number" but does not actually prove anything-at least anything worthwhile.  You HAVE to look at the actual freq response to get anything meaningful.

We had a local church that was getting several hundred WRITTEN complaints about the system each week.  NOT our install.

We went in and measured lots of places in which there were really wide holes that were 25dB deep.  NOT good.

The system was a VERY FAMOUS brand (and expensive) that would meet any rider-so no problems there.

So the manufacturer was brought in and they measured the room and told the Church that the system was +/-4dB-within the installers specs.

When I found out about this I said BS and asked for some data.  So they provided it-or at least what they "called data".

It was a graph that had SPL on the vertical axis and a hundred or so seats on the horizontal axis.

They were all within +-4dB.

HOWEVER if you actually measured THE RESPONSE in the room, you would find out that at 118Hz the system had a hump that was around 20dB louder than the rest of the freq response.

So the simple SPL meter was reading that hump and they just chose to ignore the rest of the response.

So we went in and did not sell the church anything except a couple of days labor-rehung the existing system and GAVE THEM BACK about $40,000 worth of speakers that I did not want in our redo.

The complaints went to zero.  At least until they got a new sound guy and he brought in an "expert" to retune the system and then the complaints started again--------

Using the wrong tool is not good-but it was all they could come up with so as not to embarrass their local "golden boy" who was installing lots of their gear.

For what it is worth-I redid (using existing gear-just rehanging it) 3 of their systems and the customers were much happier with the gear used the correct way-at least within the limitations of the existing products.
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Ivan Beaver
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Roland Clarke

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Re: How do you calculate PA size?
« Reply #19 on: August 11, 2014, 06:01:28 PM »

One of the big 'misunderstandings" is that "non line array" systems cannot deliver even freq/SPL front to back.

It is not hard at all-it just takes proper knowledge and design.

I have done many hundreds of systems that it is the same level at the front as it is at the back-WITH the same freq response!!!!!

Simply measuring with a SPL meter is pretty worthless in terms of saying it is the same SPL.

It gives "a number" but does not actually prove anything-at least anything worthwhile.  You HAVE to look at the actual freq response to get anything meaningful.

We had a local church that was getting several hundred WRITTEN complaints about the system each week.  NOT our install.

We went in and measured lots of places in which there were really wide holes that were 25dB deep.  NOT good.

The system was a VERY FAMOUS brand (and expensive) that would meet any rider-so no problems there.

So the manufacturer was brought in and they measured the room and told the Church that the system was +/-4dB-within the installers specs.

When I found out about this I said BS and asked for some data.  So they provided it-or at least what they "called data".

It was a graph that had SPL on the vertical axis and a hundred or so seats on the horizontal axis.

They were all within +-4dB.

HOWEVER if you actually measured THE RESPONSE in the room, you would find out that at 118Hz the system had a hump that was around 20dB louder than the rest of the freq response.

So the simple SPL meter was reading that hump and they just chose to ignore the rest of the response.

So we went in and did not sell the church anything except a couple of days labor-rehung the existing system and GAVE THEM BACK about $40,000 worth of speakers that I did not want in our redo.

The complaints went to zero.  At least until they got a new sound guy and he brought in an "expert" to retune the system and then the complaints started again--------

Using the wrong tool is not good-but it was all they could come up with so as not to embarrass their local "golden boy" who was installing lots of their gear.

For what it is worth-I redid (using existing gear-just rehanging it) 3 of their systems and the customers were much happier with the gear used the correct way-at least within the limitations of the existing products.

I'm not a great lover of "in room response" as it can be way off wack and can measure very different from the way our ears actually perceive sound.  I believe one of the things that Smaart talk about at their seminars is the need to measure the system almost as if it isn't in the room.  Room response is often subject to standing waves, reflections, that do not necessarily impact on how we perceive the "source" sound.  A classic example of this for me would be that of an orchestra playing, short of acoustic treatment the sound good or bad is only a result of the room and there is little that can be done to resolve these issues, short of positioning and aiming.

I don't argue that non line array systems can (given specialised design), give even coverage front to back and side to side, but this will require a specialist install and multiple differing "box" elements, most line arrays are travelling as 1 bass box 1 top box (given that they often have two dispersion widths) and a number of infills.

At a time when there are (in my personal veiw) maybe not so many "great" engineers about, the reality is that the average standard of concert sound these days is significantly better than it was 10-20 years ago and this is all down to the improvement in kit, particularly speakers.
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Re: How do you calculate PA size?
« Reply #19 on: August 11, 2014, 06:01:28 PM »


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