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Title: dj sub system questions
Post by: bren collins on July 14, 2015, 06:46:49 pm
i have 4 jbl stx828 subs each powered by a crown xti 4002 amp bridged..... i have a 2500 person gig coming up do you think these subs will safice???? i have 4peavey sp218 cabs but would prefer to just use the jbls what do you guys think i should do????
Title: Re: dj sub system questions
Post by: Mark Cadwallader on July 14, 2015, 08:14:26 pm
Hi Bren; welcome.  In order for anybody to offer anything more than uneducated speculation, we'll need more details.  Is your gig indoors or outdoors?  What are the measurements of the space your audience will be in?  What kind of music?  What kind of event?  What is your target SPL at what location?  Depending on your answers, you might have enough subs, or you might not.
Title: Re: dj sub system questions
Post by: bren collins on July 14, 2015, 08:58:37 pm
its a outdoor event.... around the 2000 people number, new style dj music such as jason derulo etc... its for a marathon run and its the after party its a dance/glow party theme. im wanting 110 db at 1 m away....
Title: Re: dj sub system questions
Post by: Cailen Waddell on July 14, 2015, 09:33:04 pm
1 m = meter or miles?  Cause if you mean miles you might need more speakers.  You are looking a at needing about 166 DB in output at one meter. 


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Title: Re: dj sub system questions
Post by: bren collins on July 14, 2015, 10:05:24 pm
i meant miles but i would be ok with 100 db at a mile how many more subs would i need to reach the 100 db at a mile????? thanks for all the help
Title: Re: dj sub system questions
Post by: Lee Buckalew on July 14, 2015, 10:43:33 pm
i meant miles but i would be ok with 100 db at a mile how many more subs would i need to reach the 100 db at a mile????? thanks for all the help

To get 110dB/SPL at 1 mile you would need 175 dB/SPL@3'.  This also means that no one could be very close to the actual subwoofer location without causing them physical problems.

Just running quick numbers in my head you would need 128 subs like yours running at 130 dB/SPL each to get you around 170dB/SPL.  Give or take, factoring power compression, etc.  Yes, your subs have a peak capability of 138 dab/SPL.  This would be a constant 132 and then you also get power compression, some (probably minimal) music crest factor, etc.

I don't think that this SPL level is really what you want to try to target.

Lee
Title: dj sub system questions
Post by: Scott Carneval on July 14, 2015, 11:09:19 pm
i meant miles but i would be ok with 100 db at a mile how many more subs would i need to reach the 100 db at a mile????? thanks for all the help

Are you aware of how long a mile actually is? Are you doing this gig in the wilderness? Even if you COULD hit 100db at a mile away, you'd be at 94db at 2 miles, and 88db at 4 miles. The neighbors might complain. Not to mention a single file line of 2500 people would barely reach a mile. 2500 people gathered at a stage will fill a couple hundred feet deep.

You don't have enough subs, or experience, to cover a 2500 person gig.


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Title: Re: dj sub system questions
Post by: bren collins on July 14, 2015, 11:23:39 pm
ok ive been in sound for quite sometime but i never really do spl or any of that im not tech handy and im very old school i own no digital processors and im just recently changing to jbl.... i dont fully understand what is being asked they way i always go about things is how many people around 2000-2500 requirements of gig and type of music..... never really go by dbs or spl level i just typically know what i need but since ive jsut recently switched to jblstx828s i dont know if 4 of them can do the job i used to use 8 peavey sp218 for around 3000 people.... but im assuming these jbls can do more with less speakers am i correct
Title: Re: dj sub system questions
Post by: g'bye, Dick Rees on July 14, 2015, 11:44:48 pm
ok ive been in sound for quite sometime but i never really do spl or any of that im not tech handy and im very old school i own no digital processors and im just recently changing to jbl.... i dont fully understand what is being asked they way i always go about things is how many people around 2000-2500 requirements of gig and type of music..... never really go by dbs or spl level i just typically know what i need but since ive jsut recently switched to jblstx828s i dont know if 4 of them can do the job i used to use 8 peavey sp218 for around 3000 people.... but im assuming these jbls can do more with less speakers am i correct?

No, I think not.
Title: Re: dj sub system questions
Post by: bren collins on July 15, 2015, 12:06:09 am
so what truly have i gained by going from peavey to jbl? besides people seeing me as more reputable.... which is  a great thing i was just expecting 4 jbl stx828s to out compete at least 6 peavey sp218 cabs.
Title: Re: dj sub system questions
Post by: Mark Cadwallader on July 15, 2015, 12:41:17 am
Bren, the reason I asked the questions was to try to figure out what results you are trying to get.  The requirements are very different if you are playing jazz indoors to 2000 in a 2000 seat auditorium, versus 2000 in an outdoor football stadium that holds 15,000, versus EDM at any of those places.   Outdoors with no barriers (an empty field) is different yet. I don't know where you live, but 40 acres is 1/8 of a mile by 1/8 of a mile, a pretty standard farmers field.  If a person takes up 9 square feet (3'x3'), over 4800 people fit on one (1) acre. That's how many folks fit on 1/40 of the farmers field.  If you are only filling an acre of space (or less), you need a whole lot less power than to fill a mile deep.

For reference, an acre is 43,560 sq feet.  A US football field (360' x 160') is 57,600 square feet (including end zones), or 48,00 sq feet without end zones.

As you will learn if you hang out here, details matter.  No shame in not knowing, if you are willing to learn. I learn lots of stuff here every day.
Title: Re: dj sub system questions
Post by: Luke Geis on July 15, 2015, 12:52:52 am
Until you understand the question you will never know the answer. You are essentially at this point stealing the job away from a more qualified and probably deserving person. I digress though.

The inverse square law is probably one of the more crucial math equations that effect a sound engineer. I never thought I would need to know math to do my job, but alas I am better at math now than I was 20 years ago; simply because it must be used to do the job correctly. Wattage, a speakers sensitivity, atmospheric losses and effects, cable losses, power compression, coupling, comb filtering and even terrain all have a large effect on what the end result is. Each one requires a somewhat different mathematical equation to apply for a result and being close sometimes isn't good enough. A really hot day with lots of tarmac in front of the PA can have huge implications to sound over distance as compared to that of a cold day.

You have what many would consider to be a sizable amount of power that would take care of most any normal gig with ease. What is normal though? That depends on what you know? In this case 2,500 people could be scattered over a very large area, or perhaps condensed into a relatively small area too. The system design approach may be totally different for each scenario? do you need the things to cover huge area? Simply stack the things one atop the other so they are 4 tall and forget about stereo. This will give you a pretty huge 360 deg. coverage area around the subs and help get the energy outwards in all directions except upwards. If you stack them side by side width wise you will still have good power, but you will narrow the coverage in the horizontal plane in relation to the width of the line of subs. The longer the line of subs, the narrower the horizontal coverage will be. If you can't understand what that means and why it does that your already in trouble. You can set the subs up in a multitude of ways to get a number of results in regards to their coverage and potential peak SPL. Unless you know what you need to acquire ( the question ) you can never know how to come to the answer. You can even get cardiod coverage ( directional control ) with what you have.

What you have is capable of about 143db at 3' assuming you get them to full rated power. In all reality you could at best expect to get up to about 140db and even more realistically 137db  for the long term. However no one will tolerate being close to you when your putting 130+db in the immediate area. Not to mention your tops more than likely won't keep up either. There are subs out there that can do 140+db each!!!!! So no, the JBL STX's are not all that great in terms of performance ability. The Peavey SP218 speakers actually are about the same in terms of performance to the STX's. With 8 of the SP218's you would beat STX's by 3db. The big difference between the two is the frequency response. The STX's go lower and probably sound better at performance level.
Title: Re: dj sub system questions
Post by: Lee Buckalew on July 15, 2015, 06:17:59 am
ok ive been in sound for quite sometime but i never really do spl or any of that im not tech handy and im very old school i own no digital processors and im just recently changing to jbl.... i dont fully understand what is being asked they way i always go about things is how many people around 2000-2500 requirements of gig and type of music..... never really go by dbs or spl level i just typically know what i need but since ive jsut recently switched to jblstx828s i dont know if 4 of them can do the job i used to use 8 peavey sp218 for around 3000 people.... but im assuming these jbls can do more with less speakers am i correct

Well, let's start learning.
Here is a link to a page (I don't know and therefore cannot endorse GC Audio, just liked the chart) that gives a pretty good overview of relative dB/SPL from various sources.
http://www.gcaudio.com/resources/howtos/loudness.html
LF vs. HF reduction over distance different since HF also experiences absorption in the air and not merely the same power being spread out to cover an increasing area.  Loss over distance, excluding air absorption, is typically said to be 6dB/SPL and it follows a law of physics commonly called The Inverse Square Law for point sources.

Now, on to your question re. your 4 new JBLs compared to your previous Peaveys.  How were the Peavey's powered?
If you just compare cabinet specs the JBLs are rated to get about 2x louder in peak SPL for each speaker cabinet than were your Peaveys and they have more extended LF response by almost half an octave.  The Peaveys are rated as being very slightly more efficient than the JBLs which means they would get louder with the same amplifier power until you reach the maximum for the speakers, at that point the JBLs can keep getting louder since they can handle more power.

You have essentially upgraded your sound quality in terms of frequency response and kept your SPL capability the same (depending on how you used to power the Peaveys) while taking up less room in your pack and having to now place only 4 subs instead of 8.

If your clients liked/didn't dislike how your system sounded previously then the change should be an improvement to them with the extended LF response.  If you were hoping to have this change increase the coverage capacity for your system, it did not.

Lee
Title: Re: dj sub system questions
Post by: g'bye, Dick Rees on July 15, 2015, 08:16:18 am
Two neighboring farmers had a problem with their plow horses breaking through the fence and getting mixed up.  They couldn't tell them apart, so they tried various methods to ID them, first cutting off the mane of one...but it grew back. 

They then tried putting some paint markings on one but it washed off. 

Finally they decided to measure them.  That's when they found out that the white horse was 6" taller than the black horse.

Details are important.
Title: Re: dj sub system questions
Post by: bren collins on July 15, 2015, 11:30:22 am
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.
Title: Re: dj sub system questions
Post by: Scott Holtzman on July 15, 2015, 11:56:55 am
Holy smokes....just how are you assembling all those speakers?  You do realize they are not designed to array

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Title: Re: dj sub system questions
Post by: Dennis Wiggins on July 15, 2015, 12:11:15 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.

A picture, or at least a sketch, of how you will physically setup the speaker cabinets (including placement distances) will help get you some useful advice.

Also, include each amp channel and which cabinet it will be connected to.

-Dennis
Title: Re: dj sub system questions
Post by: g'bye, Dick Rees on July 15, 2015, 12:20:46 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.

Bren...

I hope you'll stick around long enough to learn how these things work.  You may end up taking some flack and fielding very pointed questions and requests for details.  Be patient, don't take it personally and you'll have a chance to share the hard-earned knowledge of a host of real, knowledgeable professionals.

It appears that your situation is such that the sound presence will be fairly diluted over distance no matter what you do with 100' of empty space between you and the crowd.  You will likely be told to use no more than four of your tops arranged 2/side and elevated as high as safely possible, going for clarity rather than sheer volume...which you really won't be getting with by simply adding more cabinets.

What you need to understand is that doubling the number of cabinets yields not a doubling of SPL, but rather a minimal increase in volume while affording you broader coverage.  If you then array your cabinets such that their patterns overlap(all facing front) the destructive interference resulting will tend to negate any gain in SPL you might get and will certainly degrade the QUALITY of the audio.  This will all be compounded by the 100' gap.
Title: Re: dj sub system questions
Post by: bren collins on July 15, 2015, 12:35:37 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
Title: Re: dj sub system questions
Post by: Ivan Beaver on July 15, 2015, 01:00:22 pm
its a outdoor event.... around the 2000 people number, new style dj music such as jason derulo etc... its for a marathon run and its the after party its a dance/glow party theme. im wanting 110 db at 1 m away....
Just to add in the "learning process"

If you want a particular dB SPL (at any distance and any dBSPL), you HAVE to have speakers that are capable of AT LEAST 6-10dB (or more) than the level you will actually read on a meter or "experience"

That is because the meter does not respond to the peaks (even on fast response) so it is more of an average.

The actual peaks (and the maximum output numbers quoted on spec sheets) are much higher.

So don't think that if a speaker says it can produce 130dB at 1M that you will actually be able to measure it.

If you have a special "peak reading" meter, it can capture the peaks, but those are expensive and rare.

So with the 130dB speaker, you might read 120dB.  And remember that a 10dB increase is ALSO a 10 fold increase in power.

A 20dB difference is a factor of 100, and 30dB is a factor of 1000!!!!!!!!!

So not only do you have to have the speakers, but also the amps AND the power source for the amps.

IT gets real big real quick, so be VERY CAREFUL when just "throwing numbers around".

MAKE SURE they are realistic :)
Title: Re: dj sub system questions
Post by: Scott Carneval 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.
Title: Re: dj sub system questions
Post by: Mark Cadwallader 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. 
Title: Re: dj sub system questions
Post by: Ivan Beaver 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.
Title: Re: dj sub system questions
Post by: Mark Cadwallader 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?
Title: Re: dj sub system questions
Post by: Scott Holtzman 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)

Title: Re: dj sub system questions
Post by: Luke Geis 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.

Title: Re: dj sub system questions
Post by: bren collins 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
Title: Re: dj sub system questions
Post by: Scott Holtzman 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.

Title: Re: dj sub system questions
Post by: Mark Cadwallader 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.
Title: Re: dj sub system questions
Post by: Rob Spence 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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Title: Re: dj sub system questions
Post by: bren collins on July 16, 2015, 12:35:27 pm
i did 7000 people with a jbl vrx system not with prx's i guess i didnt mention that sorry and how im deploying my prx's is 2 per side with the prx's 725 with a gap in between each speaker then 35 feet back i have 2 more per side 3.3 feet apart flying..... and rob i love that idea never thought of it maybe thats just what i end up doing for this gig
Title: Re: dj sub system questions
Post by: Thomas Le on July 16, 2015, 01:03:43 pm
What Scott was trying to say earlier was that the PRX725 is not arrayable IOW those are going 90x45 which means "Hello Comb Filtering!" I admit I'm small peas compared to the rest of the guys here but even with a VRX system for 7k outdoors sounds impossible, you'd at least need VERTEC / VTX and possible some delay fills & stacks for that much on an open field.
Title: Re: dj sub system questions
Post by: bren collins on July 16, 2015, 03:39:21 pm
it was 5 vrx boxes per side vrx932's i had custom mounting brackets built for the first 2 speakers to be straight in line with each other then after that start a curve...... i followed that with a delay stack consisting of the exact same setup and then yet another delay stack not the most convenient setup but it worked and it sounded pretty well with 12 peavey sp 218's (i had to rent 4 more for this gig) all clustered in the middle each powered by qsc plx3002's bridged. and as for the comb filtering that is something i see i need to take into consideration for this gig maybe reconfigure or bring a different top system.....
Title: Re: dj sub system questions
Post by: Thomas Le on July 16, 2015, 03:56:50 pm
Uh Oh, "custom mounting brackets"???? Better throw those away before someone gets killed! Liability much?

Also, VRX is not designed to be straight boxes, only act as a curve. If you wanted straight boxes, rent proper cabs and not rely on dinky hardware.
Title: Re: dj sub system questions
Post by: Luke Geis on July 19, 2015, 02:29:56 pm
15 years of doing this and you have not learned the most basic of math to do what we do? Your mentor left out some very important things. The questions you pose are rudimentary. They are the first things you need to know in order to spec a system for a gig. I can do sound for 7,000 people too using only an 8" EV ZX1, as long as they are running by it single file.

This is easy. I pretty much already told you what your subs are capable of. Leave the SP18's at home and just run the 4 JBL's. Those will outrun your tops anyway. It sounds as if your stuck with a more remote location so bring as few a number of speakers to do the job. The PRX will not splay together well. You could get away with 2 per side at best. If you bring more, set them up as delay speakers. For the love of god do not bring 8 tops and try to splay 4 of them per side............

Less is going to be more in terms of quality. Quantity is another thing all together. As it is you should be able to just have enough real spl to do the job with the tops. I don't see any reason why the 4 subs won't keep up. If your going to bring all your tops and run delay lines, be sure you have the proper processing to do it too. A delay line to function properly must have the speakers time aligned and the goal is to not increase volume as you go along, but to maintain it. That is to say that your not blasting all the speakers at the same volume. The delayed speakers will be lower in volume to simply help maintain the SPL from the front to the back of the venue. Remember the distributed system? If the two speakers are more than 20' apart you get destructive delay. With a delay line the speakers are purposefully delayed to eliminate that and account for a greater distance between speakers. As soon as you get between two speakers the delay is wrong and you will again have problems. So you want to keep it so the delayed speakers are not loud enough to be heard over the speaker it is supporting when you are between them. It should work much like a distributed system. The SPL at the first delay line is pretty much the SPL that will be maintained from then on. You can usually get away with 1-2 delay lines within a 100' span. Ideally you want to keep the delay lines within about 50' of each other. Beyond that and they are too far apart to really work well. It just sounds like another speaker making more volume. When done well you should be able to walk down the venue and not be able to really tell when you have walked between two sets of speakers. It will simply hold SPL until you start getting to the main system where it starts to get louder.
Title: Re: dj sub system questions
Post by: Scott Holtzman on July 20, 2015, 04:47:30 am
15 years of doing this and you have not learned the most basic of math to do what we do? Your mentor left out some very important things. The questions you pose are rudimentary. They are the first things you need to know in order to spec a system for a gig. I can do sound for 7,000 people too using only an 8" EV ZX1, as long as they are running by it single file.



Yes, when your main defense is "I have a mentor from claire bros (sic)" you know you have reached the end of any semblance of a discussion. 

BTW Clair Brothers is a manufacturer and integrator.  Clair Global is the production house.

We have given you a ton of information.  When you are ready to "sharpen your saw (see 7 habits if you don't know the reference) feel free to come back with cogent questions.  We will still be here (we as in the collective forum, not me as an individual speaking as the collective  ::) )
Title: Re: dj sub system questions
Post by: Mark Cadwallader on July 22, 2015, 02:20:53 pm
Bren, did you have the chance to A/B your new and old subs?  If so, what was your impression?
Title: Re: dj sub system questions
Post by: john sanders on July 24, 2015, 09:47:50 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.