Question about how many power circuits we should be using (and addition of new cabs)

[Jealousblues]

Hey guys just want to give a big thank you for all the help so far with my other threads.

 

Ok, heres our situation

nothing huge but Im wondering about power.

 

We do lots of weddings and private shows with our own PA

and lots of outdoor gigs where we really could use a little more PA

 

right now we have two JBL SRX 728 subs (passive double 18's) and two JBL PRX two way tops with the two 15" speakers and sometimes we use the PRX single 12" as well for sound out to our side at weddings or a little extra at outdoor gigs.

two crown XTI 4000 amps to power the subs.

We are thinking about picking up two more of the double 18"s if we can find them.

We currently run 2 keys, a pod (guitar effects), VDrums, and our presonus mixer and amp rack and LED lighting (we do have 2 moving lights and 2 scanners that are not LED however, dont know how much power that takes. I know the LEDs are much less)...so I dont think any of that other than the speakers are huge power draws?

 

Right now we use 2 20 amp circuits to power that. One of the subs and one for everything else. IF we can get three we will use that as well.

We almost never have any issues unless the place is really old or has really crappy power.

 

I assume thats the correct way to run that?

 

Anyway I was wondering if we got the new subs (and maybe two more tops in the future) if we are going to run into any power troubles

and if so how many circuits should we be using and how would you run it?

 

(say two sub amps on one circuit and two more on the other and the rest on the third ect..)

 

I just dont want to buy more speakers and then find out we cant really even use them or start blowing power.

 

thanks guys, I really do appreciate your knowledge and how much you have helped me over the years.

[RoadRanger]

two crown XTI 4000 amps to power the subs.

Are those amps bridged?

 

[Tomm Williams]

Are those amps bridged?

 

You're asking because the OP states he's using two amps for two cabs?---------seems possible, yikes!!

[agedhorse]

Are those amps bridged?

 

Certainly opens up the possibility of power problems in addition to other problems that make me big money

[Jealousblues]

yes they are bridged as far as I know

one amp for one cab

 

I didnt set up the system (and im not really the one in charge of it) but I am the one who would go online and ask these kinds of questions ;-)

 

We have have about 4 different sound guys here with their own companies we know look at our system and give us their takes on this and that and none of given the facepalm on that so im eager to know what we are doing wrong.

Im not sure if you are saying we are overpowering them or underpowering or what not. Weve been running them this way for 2-3 years id think and we have never had any problems with the subs, we do red line the amps from time to time (nothing constant or anything just happens every once in a while at least once a show however) and we run a lot of low end. Its not distorting or blown or anything.

Id really appreciate your guys thought and criticisms.

 

As I understand it bridged it is 3,200 and thats what the JBLs are rated for

[Tomm Williams]

SRX 728 specs 1600watts@4ohms continuous. Crown XTI4000 bridged 3200 watts@4ohms. Probably more "headroom" than you need. you have plenty of power to add a pair of 728's in stereo without adding amps.

[Jealousblues]

this is where I its hard because im kind of a middle man here

I dont run the system and I dont know as much as you guys...

 

but I know the setting on the subs are "brgd subs" (or something like that for bridged subs).

we do hit red on the subs quite a bit fwiw maybe upto maybe a couple times a gig. Nothing out of control or anything where its sustained or anything where its wildly loud or anything other than it puts out a lot of low end.

 

Id say we run this system 15 times this entire month and thats a typical month for the last couple of years.

everything is working well after all of this.

 

perhaps there is a piece of the puzzle im missing and not telling you guys?

 

agedhorse and others were explaining the power ratings in another thread recently

and im still trying to learn this. so bear with me guys ;-)

[agedhorse]

 

Weve been running them this way for 2-3 years id think and we have never had any problems with the subs, we do red line the amps from time to time (nothing constant or anything just happens every once in a while at least once a show however) and we run a lot of low end. Its not distorting or blown or anything.

 

 

... yet!

 

I suggest that you read some of the old threads on powering cabinets. There's a lot of good info that might be applicable to your situation.

 

What processing parameters are you using on your amps, are you POSITIVE that they are set correctly? I have seen a lot of these drivers damaged by overpowering just like what you have in your rig now. All it takes is a lapse of good judgement, an accident, or just plain dumb bad luck.

[Jealousblues]

im my mind when I see the amps redline (on hits not continuous) I think there is no more headroom

and from reading your post above I would believe that redlining under those conditions would make the subs toast, correct?

 

So maybe there is something im ignorant of or that I am miscommunication.

 

Ill be honest, we arnt quiet and we do have a lot of low end (I know its all relative) as is.

 

 

 

 

so id believe with what has been communicated to me our speakers should be toast?

And since they arnt I think Im missing something personally.

 

 

if you are saying these amps way over power the subs

maybe the thought when they were purchased was that we could always add others on them in the future?

[Jealousblues]

Agedhorse, I cant tell you that. Ive not messed with them and no one in the band has changed the settings on them.

We have had a couple guys that have their own sound companies in town and their own systems set them up, check them out over the years.

I know its easy to say "blah blah blah soundmen" and on the internet you have no idea who im talking about, but they are guys who do know what they are doing and have done sound for years with real systems (better than ours fwiw, I know you work with huge systems)

 

I trust those guys over any research I could do in a weekend, not that I wont educate myself, just I dont trust my judgement at this time

 

 

does it sound really outlandish that our system could be set as I have described and that its still working right now with zero problems with the subs?

As I said we run them pretty hard and 15 gigs where we provide our own sound is typical a month for the last 3 years

so its made it through aprox 540 gigs this way...

 

so is what im saying

"BAT{censored} INSANE! This absolutely should be toast by now no questions asked"

or is it

"this guy doesnt know what he is telling us and he is obviously missing something in his description"

or is it

"they are running it hot but its ok...but its close to where a problem could occur"

[Jealousblues]

also thanks for bearing with me

I know its difficult to explain things like this to people who arnt very knowledgable

[agedhorse]

What I am saying is that if you are driving them this hard, you are causing gradual damage of the mechanical suspension components... ie. like stretching a spring slightly beyond it's limits. Over a period of time the materials will fatigue and no longer function the way they were designed. If you look at speaker reliability curves (this is what I do for a living), you will see that power compression causes limits in SPL gain at about the same time as the reliability begins to fall. A driver may be capable of 1000 hours at say an "RMS" rating of 800 watts and when driven the dame way to 1600 watts the driver may only be capable of 100 hours. The question is where on the curve do you want to operate?

 

Those are expensive drivers to recone (I ran a recone shop for many years and have done a lot of JBL product), and the benefit of getting 2 more cabinets and running the cabinets at 1/2 the power you are now (same total power) will be on the order of 7 or 8dB when you factor coupling and power compression into the equation. I think it will sound better too.

 

This is the kind of stuff that those of us who develop product for this industry consider whenever we are developing new products. There is the ongoing battle between the engineering types who strive for reliability metrics and the marketing types who strive for sales and sales numbers. If stretching things improves sales, that's their job, but is it really in the best interest ofthe customer or the long term reliability of the product? Probably not. I have fought this fight for 30 years, there's a lot pf products that I have designed that you guys may be currently using, and so far I have won most of the time. As a product development engineer, I generally side with the engineering argument though I may alter the design to cover more marketing ground if budget and reliability make it work.

 

Here's one link that shows some ofthe factors:http://acapella.harmony-central.com/showthread.php?1802430-Amp-Bridging-question...&highlight=speaker+failure+modes#

[Jealousblues]

so big vote there for two more cabs

 

and if im reading you correctly (just checking to be absolutely sure)

id just use the same two amps im using now

and the same power draw so no need for extra power circuits

 

 

just out of curiosity how much would a recone be on those?

[RoadRanger]

They probably already have their FS (resonant frequency) lowered such that they no longer match the box tuning . You might compare them to the new ones you get for output and see if they would benefit from reconing. Yes, you can use the two amps to power four boxes but you have to un-bridge them and run one box per channel. They will actually draw a bit less power than now and run cooler and be louder .

[agedhorse]

They probably already have their FS (resonant frequency) lowered such that they no longer match the box tuning . You might compare them to the new ones you get for output and see if they would benefit from reconing. Yes, you can use the two amps to power four boxes but you have to un-bridge them and run one box per channel. They will actually draw a bit less power than now and run cooler and be louder .

 

The advantage in overall efficiency will be gained from less power compression (that's the LEAST efficient operating point ofthe system) as well as improved coupling gains. It's really a win-win situation all around (IF you don't mind the additional cabinets)

[Jealousblues]

does it make any difference if you stack the cabinets or if you have them side by side (perhaps even tied to each other with ratchets)

[Unalaska]

I'm in the wedding band circut, I run sound for a lot of different bands at weddings both outdoor and indoor. My main system is JBL MS105 (reloaded with better guts and biamped) and SP128s (2x JBL 2242's). Never, and I mean never have I needed double stacks for anything under 400 or so. I keep the SPL around less than 100dB on the dance floor, people at weddings want to talk etc and enjoy time with thier family. All these are being driven with less than 1100w per box. I will run double stacks for very large corporate and outdoor festival type settings but really it's not that often.

 

I had a pair of 728's for a while, I really liked them, sold them because they didn't integrate with my line up of subs. But at 1100w each they were great boxes, very deep sounding and work well in multiples. I guess I can't see dragging 4 out for a lot of gigs. 15 a month is every other day, that's a lot of gigs, it's a good reason to be scaleable too. Match your top boxes and center cluster the subs when you need more out of the rig, you'll be suprised.

[minn12]

 

yes they are bridged as far as I know one amp for one cab I didnt set up the system (and im not really the one in charge of it) but I am the one who would go online and ask these kinds of questions ;-) We have have about 4 different sound guys here with their own companies we know look at our system and give us their takes on this and that and none of given the facepalm on that so im eager to know what we are doing wrong. Im not sure if you are saying we are overpowering them or underpowering or what not. Weve been running them this way for 2-3 years id think and we have never had any problems with the subs, we do red line the amps from time to time (nothing constant or anything just happens every once in a while at least once a show however) and we run a lot of low end. Its not distorting or blown or anything. Id really appreciate your guys thought and criticisms. As I understand it bridged it is 3,200 and thats what the JBLs are rated for

 

 

JBL recommends from 1600-3200 per cabinet, so you're giving them the high end (the 'continuous' rating). I've also run JBL subs at the high end of their ratings with zero problems for many years, so if you are careful and have correct settings, you should be alright. Others will advise differently, and recommend a far lower power level. You have run these for 2-3 years with no problems. I'd try to avoid any 'redlining' of power amps, however. It's my opinion that most JBL subs sound better and come to life when run at the higher end of JBL's power recommendations.

 

Adding two more subs and more tops will require more power to operate, so yes, you will need to have more circuits available, if not the need for your own power 'distro'. This would especially be true if you have your own stage lights.

[Craig Vecchione]

 

JBL recommends from 1600-3200 per cabinet, so you're giving them the high end (the 'continuous' rating). I've also run JBL subs at the high end of their ratings with zero problems for many years, so if you are careful and have correct settings, you should be alright. Others will advise differently, and recommend a far lower power level. You have run these for 2-3 years with no problems. I'd try to avoid any 'redlining' of power amps, however. It's my opinion that most JBL subs sound better and come to life when run at the higher end of JBL's power recommendations. Adding two more subs and more tops will require more power to operate, so yes, you will need to have more circuits available, if not the need for your own power 'distro'. This would especially be true if you have your own stage lights.

 

 

He can run another pair of subs without adding more amps. Read what agedhorse wrote...power compression prevents the speaker drivers from increasing their audio output despite throwing a LOT of power into them. Doubling the speakers allows more drivers to better use the available power. Less distortion is a side benenfit as well.

[agedhorse]

Minn12... how long would you like your sub drivers to last? 3 years? 5 year? 10 year?

 

I have a lot of drivers in my inventory, I can't afford to have to recone every 5 years (that would cost me about $20k every 5 years) so if I get 15 years out of drivers, I save $90k over the 15 years which is much more valuable to me than driving the piss out of my stuff to try and gert every last dB. That last few dB comes at a very high cost.

 

If you think you haven't damaged the drivers, it might be enlightening to run a parameter check (via something like Cleo) to see how far from factory spec. your drivers have deviated and when you then run a performance test you will then see how much performance you have lost. You may have already lost more than you originally hoped to have gained by going from 1600 to 3200 watts. In fact, I'm pretty confident that this is what you would find.

[lifeloverwg]

 

He can run another pair of subs without adding more amps. Read what agedhorse wrote... power compression prevents the speaker drivers from increasing their audio output despite throwing a LOT of power into them. Doubling the speakers allows more drivers to better use the available power. Less distortion is a side benenfit as well .

 

 

I'm convinced that for a sizable number of users, the sound they "like" when the subs "really come alive" is the sound of the increased distortion caused by the power compression produced by higher power being thrown at them.

 

Not my favorite type of sub sound, but it seems to be popular with plenty of operators I see and hear.

[RoadRanger]

^ +1, except that the distortion is mostly cause by exceeding xmax - and I don't mind that "sound". I use a Waves MaxBass unit that does the same thing of adding the right kind of harmonic distortion without overexcursioning the drivers. I can get significant "virtual output" down into the 20hz range with it even with my subs which all cut off at ~50Hz .

[agedhorse]

I like the sound of drivers failing , it's just like money to my ears... wait it IS money to my ears when they aren't mine. I have 20 drivers sitting here in the shop being reconed for a customer and that is welcome income at their expense.

[minn12]

 

What I am saying is that if you are driving them this hard, you are causing gradual damage of the mechanical suspension components... ie. like stretching a spring slightly beyond it's limits. Over a period of time the materials will fatigue and no longer function the way they were designed. If you look at speaker reliability curves (this is what I do for a living), you will see that power compression causes limits in SPL gain at about the same time as the reliability begins to fall. A driver may be capable of 1000 hours at say an "RMS" rating of 800 watts and when driven the dame way to 1600 watts the driver may only be capable of 100 hours. The question is where on the curve do you want to operate?

 

 

 

Well, the OP states he has some 540 shows on those subs while running them hard with no failures. At a typical 4 hours per show, that would be over 2000 hours on the subs with no failures. Based on the above, they should have failed mechanically long ago, but they haven't. The OP has had several sound company operators look at his system and states no one has had a problem with the setup. Based on that and the long performance without failures, I would assume it's well set up. Powering speakers with the 'program' power rating rather than the 'continuous' is not uncommon, and properly set up, does not necessarily mean a drastically shorter life. Many people have good results either way.

[agedhorse]

 

Well, the OP states he has some 540 shows on those subs while running them hard with no failures. At a typical 4 hours per show, that would be over 2000 hours on the subs with no failures. Based on the above, they should have failed mechanically long ago, but they haven't. The OP has had several sound company operators look at his system and states no one has had a problem with the setup. Based on that and the long performance without failures, I would assume it's well set up. Powering speakers with the 'program' power rating rather than the 'continuous' is not uncommon, and properly set up, does not necessarily mean a drastically shorter life. Many people have good results either way.

 

 

Maybe he is not running them as hard as he thinks, manbe the processing is st well or that the limiters are set below the maximum rated amp capability, etc.

 

I am saying from MY experience designing and servicing this stuff that it's not the best approach.

 

Out of curiosity, how many speakers have you reconed? Have you ever handled customer service or warranty support for a speaker product?