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Author Topic: dj sub system questions  (Read 9872 times)

Scott Carneval

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Re: dj sub system questions
« Reply #20 on: July 15, 2015, 01:08:21 pm »

now that i know it would be about a half acre maybe alittle more is where the people will be but its a flat field about 2 acres big..... and thanks guys im starting to learn details matter a little more than i thought. im wanting to get my subs as loud as i can because what i do know is the first 100 foot there will be no one there..... as for my highs im running 8 prx712's and 2 prx 725's.... hope to change these out in future for complete stx system.

I don't understand the 100' gap.  I would try to start my speakers as close to the audience as possible.  Then take the 8 prx712's and make two delay towers per side.  So you'd have the 2 725's at the front, then 4 712's about 75' back, and another 4 712's about another 75' back from those.  But even with all these speakers, you won't be providing 'festival quality' sound for 2500 people.  Unless it's maybe a jazz festival.
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Mark Cadwallader

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Re: dj sub system questions
« Reply #21 on: July 15, 2015, 04:05:25 pm »

now that i know it would be about a half acre maybe alittle more is where the people will be but its a flat field about 2 acres big..... and thanks guys im starting to learn details matter a little more than i thought. im wanting to get my subs as loud as i can because what i do know is the first 100 foot there will be no one there..... as for my highs im running 8 prx712's and 2 prx 725's.... hope to change these out in future for complete stx system.

Please note that my 9 sq foot/person figure is an easy-to-visualize example. It might represent a reasonable average density, but then maybe not. YMMV.  I don't know if there is a generally accepted average density number used by folks in the industry for planning/estimation purposes. 
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Ivan Beaver

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Re: dj sub system questions
« Reply #22 on: July 15, 2015, 04:09:29 pm »

Please note that my 9 sq foot/person figure is an easy-to-visualize example. It might represent a reasonable average density, but then maybe not. YMMV.  I don't know if there is a generally accepted average density number used by folks in the industry for planning/estimation purposes.
Close to the stage is a lot closer than that.  More like 6 square feet or less.
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Mark Cadwallader

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Re: dj sub system questions
« Reply #23 on: July 15, 2015, 05:16:43 pm »

Bren, is there a physical barrier that is keeping your audience 100' away?  If not, why do you expect that nobody will be within 100' of you?
« Last Edit: July 16, 2015, 08:22:20 am by Mark Cadwallader »
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Scott Holtzman

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Re: dj sub system questions
« Reply #24 on: July 15, 2015, 06:55:02 pm »

i would post a sketch of the system but i cant figure out how to upload it.... again thanks for all the help im receiving

Bren - Are you the Ben Collins in OH?  If so I am in OH and can lend a professional hand. 

Some of the most experienced folks here have pointed out, you are way behind the curve on the level of job you are talking about.  Partnering with an experienced company, possibly even at a loss, will save your reputation and will earn you experience in what the job actually entails. 

There are many forums with DJ's and Sound Providers, this forum is different.  Many of the folks here are touring professionals, the folks you see working and running the largest and/or most prestigious events are in these rooms helping and moderating.  The quality of knowledge in this forum surpasses anything else on the Internet.  The reason I say this is it's easy to get put off, and run to a forum that will just reply "what a system" by the shear quantity of speakers you have.  They would not know audio if it hit them in the head.  These are the guys that you go to a show and it's loud as all get out but can't understand the lyrics, or the subs thumping but half the bass octaves are missing.  Loud is easy, something people want to listen to is hard, loud and good is even harder (and more expensive yet).

You need to slow down and take a deep breath, you say you don't know how to upload a picture yet every time you hit reply there is an attachments + sign and the word attachments under the text box.  Did you hover your mouse over each icon to see what they do (the label comes up).  Computer literacy and understanding advanced technical concepts are called "skill tracks" and something educators watch for.  Many of us here consider ourselves educators on some level.

It sounds like this is a very important event, in addition to the drawing (great place to start a discussion) would you mind taking a moment and telling us if you have a rider or tech sheet from the event provider?  Where are you getting your numbers from?  Are these incorporated into a contract?  If so I bet there is a provision for liquidated damages on non-performance.  Usually providers of large events are vetted.  So in a polite way I am asking how you got into this.  It makes a difference, if you were drafted, volunteered etc.

Let's keep on going.  8)

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Luke Geis

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Re: dj sub system questions
« Reply #25 on: July 15, 2015, 11:13:25 pm »

I think we can save him a bit of the headache. The speakers he has will not be of much use past 100'. Lets say for the sake of argument that they are actually capable of acquiring 130db. This is the 3' ( 3.28' actually as it's actually rated at 1 meter, but whatever ) possible SPL. So the ISL will dictate that at 100' he would have about 100db. This is with one speaker and adding more may help gain a few more db, but possibly not after comb filtering? So this is assuming full tilt boogie though. No left over room and if it's not enough, it's not enough. Meanwhile anyone that encroaches within the 50' mark will be absolutely blasted with volume.

However we haven't introduced a couple very important factors. First and foremost crest factor and power compression. So 130db is the peak SPL possible, not the average spl and the crest factor of the music and or vocals will be lower in average SPL than the peak spl generated. luckily speech and pre recorded media is about the same with about a -10db crest factor. So this means that you are likely only going to see 90db spl levels actually generated at the 100' mark. It gets worse though....... This SPL is based on the peak ability of the speaker, so it will be working pretty hard to do this. Power compression is the electro mechanical reduction in the transfer of energy. In other words the hotter the coil of the speaker gets, the more resistance it creates to the flow of electrons and therefore the lower it's transfer of electrical energy into acoustic energy becomes. This loss in output can be as little as 3db to as much as 6db or more!. So now after a short bit of time your SPL read at 100' will be closer to the 83-86db mark. This is not going to be enough if the crowd starts yapping away. And this assumes the high end content of the speakers doesn't also deflect upwards and get totally absorbed into the atmosphere before it gets to the listener.

The best way to combat this problem is to bring the speakers closer to the crowd. Your looking now at a distributed system. It is best to keep the speakers within about 20-25' of each other or significant delay will occur making speech harder to understand. you will also want to have enough speakers to spread across the entire listening area. So if you have a 100' span of area you need to cover you would in theory need at least 5 speakers to cover it well. A football field is 300' and to have coverage where there is no highly damaging delay would then require 15 speakers! Can you do it with less? Yes, but you will have to turn it up louder to get the SPL up in the thirds of each pair of speakers and this increases the chance that you will hear more than 1 speaker at a time. When you hear more than 1 at a time you get delay and delay causes a loss in intelligibility. When the speakers are located within about 20' - 25' of each other, the sound that is heard between them is close enough that the delay is not as destructive and it would require less overall SPL to be heard over the coverage area. And since there is less overall SPL they don't effect the sound from other speakers further away as much either. It blends really well and as you walk by each speaker they start to blend evenly and by the time you can hear both equally well your directly between them. Beyond 25' though and this effect is minimized causing more problems than solutions.

So when I say you need to know the question before you can come to an answer you can see how it totally effects the outcome. It sounds like you only have a total of 10 speakers to distribute. This would cover an area about 250' wide to about 50' deep if you spaced the speakers 20' apart. This is equivalent to about 12,500 square feet or .28 acres ( that's right, just over 1/4th of an acre )........... 2 acres is 87,120 square feet. So this leaves you about 74,620 square feet shy........ 2 acres would measure out to about 295' x 295' square. A football field is 300' X 160', so you can see how your not going to make 10 speakers work.

This all assumes you need to cover the entire 2 acres evenly with sound. So you need to know the actual area you need to cover, as this can change the outcome greatly. Unfortunately your speakers will not play together well when splayed since most are 90 deg boxes. This means that you can't really get as much free power as the number of speakers suggest. In all honesty if you plan on running the system in a conventional stereo rig, your better off only showing up with 4 total and leaving the other 6 at home.

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bren collins

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Re: dj sub system questions
« Reply #26 on: July 16, 2015, 02:17:58 am »

Ok maybe I've been kind of scattered brained out of it not showing my actual experience I have been a sound engineer for 15 years now I was taught by a man who worked for Claire brothers audio as a main sound tech I have actually done this gig for 4 years and it's definitely not the biggest I've done I've done a 6-7000 person event with ease.... the questions I guess we're kinda confusing or maybe I didn't fully understand or was just kinda pushing them aside that would be my fault. I'm providing sound for about 3/4 a acre the main area is 100 feet approximately from the area I'm designated to be set up this is because it's a festival type with many vendors and is unlikely people would come much closer except for maybe some announcements..... I know my mids and highs are fine I have a set up in my mind I hope to use but if not I will be deploying more speakers if needed as for my subs I have a total of 8 peavey sp 218 and 4 Jbl stx828s I was wondering if these 4 would suffice just save me setting up 4 more I was posing the sp 218 with 2000 watts a piece I'm now powering the Jbl's with 3200 watts each both speakers are 1 watt equals 99db at 1 meter but I am providing greater power to the jbls I was wondering is that gonna cut it I am not about to cut the gig shortens if required I will deploy the other subs as needed as far as the picture uploading I clicked it not working to weird maybe my laptop....   I really see a lot of you guys are far experienced on this forum and I feel I have a lot I can and will learn from this it will greatly help me thank you all for the responses
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Scott Holtzman

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Re: dj sub system questions
« Reply #27 on: July 16, 2015, 06:52:41 am »

Ok maybe I've been kind of scattered brained out of it not showing my actual experience I have been a sound engineer for 15 years now I was taught by a man who worked for Claire brothers audio as a main sound tech I have actually done this gig for 4 years and it's definitely not the biggest I've done I've done a 6-7000 person event with ease.... the questions I guess we're kinda confusing or maybe I didn't fully understand or was just kinda pushing them aside that would be my fault. I'm providing sound for about 3/4 a acre the main area is 100 feet approximately from the area I'm designated to be set up this is because it's a festival type with many vendors and is unlikely people would come much closer except for maybe some announcements..... I know my mids and highs are fine I have a set up in my mind I hope to use but if not I will be deploying more speakers if needed as for my subs I have a total of 8 peavey sp 218 and 4 Jbl stx828s I was wondering if these 4 would suffice just save me setting up 4 more I was posing the sp 218 with 2000 watts a piece I'm now powering the Jbl's with 3200 watts each both speakers are 1 watt equals 99db at 1 meter but I am providing greater power to the jbls I was wondering is that gonna cut it I am not about to cut the gig shortens if required I will deploy the other subs as needed as far as the picture uploading I clicked it not working to weird maybe my laptop....   I really see a lot of you guys are far experienced on this forum and I feel I have a lot I can and will learn from this it will greatly help me thank you all for the responses

You did 7000 people with PRX's.  You didn't answer any of our questions on how you are going to deploy all those mid/high boxes.  15 years in the business and training from an experienced tech you have shown to be lacking in basic concepts (such as the logarithmic decibel scale to express SPL), comb filtering and destructive interference.

If you have a way to array these cabinets and avoid the pitfalls we would like to learn.

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Scott AKA "Skyking" Holtzman
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Mark Cadwallader

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Re: dj sub system questions
« Reply #28 on: July 16, 2015, 08:43:42 am »

Bren, I respectfully suggest that you just run what you have, and those who want to hear a higher level will just come closer to you. If there are vendors in the area, they will probably appreciate that it is not club/concert level where they are trying to do business. 

As to which sub to bring, at some point you will just have to compare the subs out in the real world. Try the new subs; if they don't get loud enough for your tops, turn down the tops until you have the right balance.

Speaking as an audience member, it will probably be louder than I want to be subjected to at a non-concert event. But I'm old, and I generally think providers usually over-estimate how loud they should run.
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Rob Spence

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Re: dj sub system questions
« Reply #29 on: July 16, 2015, 10:54:44 am »

You could always bring both sets of subs this time (it would look impressive) and run one set for a while, then switch to the other set to compare (just have to move a couple of Speakons ).

Then you will know...


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