General PA setup for band

[Chris__H]

Hi All, this is probably pretty basic to most of you sound engineers out there, but I recently purchased a PA system with passive JBL Speakers - 2xJBL SRX715 speakers, 2 x JBL 718 SUB bins, a Dbx 223XL and 2x Behringer iNuke 6000 amps and mixer for a band project.

I need some tutoring on how to run the cables to set them up please:

Could someone with some knowledge on such things kindly draw me a diagram from the mixer L and R outs to the Dbx to the Amps through to the right way to run the cables to the speakers please Oh and some help on Dbx settings please!!

Also I'm a little reluctant to run the iNuke6000 amps as I have read some people say they lack reliability? So any thoughts on some reliable amps that would match the system that won't cause mortgage foreclosure would be really helpful too! (But in the end I'm sure reliability doesn't come too cheap either!).

Anyway thanks for reading my post and any help will be really really appreciated. Thanks Peeps

I have a Drive link to the speaker and dbx specs below:

https://drive.google.com/drive/folders/ ... share_link

[Wonks]

Hi and welcome.

The good news is that what you've bought all seems a very good match.

The tops and sub have the same 800W power rating, the sub is just 1dB less sensitive (which you probably won't notice) and the power amps are 1600 Behringer Watts (probably music power) into 8 ohms, so around 800W RMS. So no worries there.

Crossover

So start by running from the mixer main L+R outputs to the L+R inputs on the crossover. I suggest you'll want to run it in Stereo 2-Way mode.

On the front panel, set the input gains to zero.

I'd probably set the 40Hz low-cut filters to 'in' unless you have very low synths or 5-string bass guitars. This saves a lot of unwanted low-frequency rumble which can't really be heard and takes up amplifier power which can be better used on the bass frequencies you can hear.

The JBL documents recommend an 80Hz crossover frequency, so set the crossover frequency dial to 80hz.

The low output and high output knobs can be set to 0dB for now. You may want to adjust the low output knob slightly if you want a bit more or less low bass, but to start with, I'd keep the outputs balanced.

You shouldn't need to touch the phase invert buttons, leave them 'out'. These are useful if mixing tops and subs from different manufacturers and where the polarity of the speakers might be different, but with an all JBL-system you should be fine.

On the back panel, I'd set the stereo/mono switch to stereo. You could have a mono sound if you want, but most people tend to have the mixer set up for 'dual mono' with most mono channels set with the pan in the middle and maybe stereo inputs from keyboards, drum overheads panned L+R and any reverb effects providing a bit of true stereo interest.

The low sum switch position is up to you. I'd probably have it set to 'summed' as the 80Hz crossover frequency is about the point where you lose any stereo information from the subs, so you might as well have the same sound coming from each sub. You probably wouldn't notice any change in sound if you had it in 'normal' unless there was a panned bass sound, where you'd probably just notice a loss in volume rather than the sound coming from one sub.

The x1/x10 frequency switch for the crossover should be in the x1 position. The x10 is for when you are using the crossover for splitting the signal between the main/mid driver and the tweeter, so maybe in the 1.2kHz-3kHz region.

You'll now need to connect the crossover outputs to the power amps.

Power Amps

You've got a choice between using one power amp for the tops and one for the subs, or using one power amp per side. It's common on PAs in general to have more subs than tops, and bigger power amps for the subs than the tops, but here the number and power are the same, so it's up to you. It's probably easiest mentally to have an amp for the tops and an amp for the subs, so that if you want to adjust the output volume settings for the tops or the subs, you set the dials the same on the same amp.

I'll assume we go for one amp for tops and one for subs

I'd label the amps front and back so you don't get confused when plugging in or adjusting volume dials.

The input section on the back of the amps has combi-XLR/Jack inputs. I'd run XLR-XLR cables between the crossover outputs to the amp inputs. Channel One and Two 'High' outputs on the crossover to the channel A and B inputs on the power amp. It doesn't really matter which input it goes into as long as you are consistent throughout and your mixer Left output ends up going to the speakers you want to call the Left speakers (as you've got stage left and audience left depending on where you view from), and likewise for the Right output.

Again, a bit of tape and marker on the inputs and outputs with the same terminology can help to avoid confusion.

The mode switch should be set to stereo and the crossover switch set to 'full range' (as the crossover frequency is already set by the dbx unit). I can't find anything in the Behringer docs as to what the amp crossover frequency is set to, so best avoided).

Then it's a question of running speaker cables with Speakon connectors out to the tops and subs. The cables just need to be the standard sort of Speakon/Speakon cable (which are normally the 4-terminal type) , with terminals +1 and -1 connected at each end.

Speakers

On the sub there is a switch in the recessed speaker socket panel with selection for NL4 +1/-1 or +2/-2. Set this to +1/-1 on both subs.

Though it doesn't really matter as to which of the two Speakon sockets you plug into as they are wired in parallel, I tend to always use the top socket.

On the tops there is a passive/bi-amp switch. Set this to 'passive'

Speaker cables

The cables need to be sized for both the maximum current that will pass through them and also the length of cable run. For 800W into 8 ohms you could just get by with 1mm2 cable, but if you assume that the occasional peak current will be double for those short 1600W bursts, them 1.5mm is really your minimum cable size.

But the longer the cable run, the higher the resistance of the cable will be and the less power will reach the speakers. So to allow for reasonable cable distance, I'd use 2.5mm conductor cables. Physically these are a bit more robust than thinner cables, whilst still being reasonably flexible.

[The Red Bladder]

1600 Behringer Watts (probably music power) into 8 ohms, so around 800W RMS.

A new power rating - Behringer Watts! So it's 2 Behringer Watts = 1 Watt (RMS).

[Wonks]

They generally quote either music (RMS x 2) or peak power (RMS x 4).

[Sam Spoons]

As far as powered speakers are concerned that's pretty much how it's done across the industry these days*. The more 'professional' manufacturers of discrete PA amplifiers do still use a properly defined measure (such as RMS@1kHz).

* TBF it actually doesn't matter as long as they quote a properly defined max SPL number (which is much more useful in practice).

[ef37a]

"* TBF it actually doesn't matter as long as they quote a properly defined max SPL number (which is much more useful in practice)."

And of course there are no RMS" watts but that ship has sailed I fear, along with that oft misused term "saturation" !

Dave.

[Sam Spoons]

Just consider the straight man Dave

[Chris__H]

Wow Wonks, that is super informative! You're the coolest! Thanks you so much for shedding a big beam of light on this for me! Super cool and I can't thank you enough

[Wonks]

I’m sure you’ll have other questions as you progress, so don’t be afraid to ask. For instance, you haven’t mentioned any monitoring system yet. You may already be fine with that, or it may be something you still need to deal with.

[Chris__H]

Regarding monitoring, we will be using a Soundcraft ui24R coupled with IEM systems and the drummer has a wired unit.

Do you think Behringer inuke 6000's will stand up ok? I was thinking it maybe a good idea to get a spare nuke 6000 just in case one goes down?

[Wonks]

I’ve got no experience with them so can’t say. I’m sure most work just fine and as always you only hear about the one’s that don’t. And you never know how hard they've really been driven.

It never hurts to have a spare amp, though there are alternatives.

You do have the ability to run the whole rig in mono from just one amp. The tops and subs are both rated rated as 8 ohms and each amp channel can drive into 4 ohms, so you can run the tops in parallel and the subs in parallel and still get the same output volume.

This fallback configuration may make it easier to have one amp doing a side (one top and one sub) rather than one amp for tops and the other for subs.

You'd then simply set the crossover for mono operation (that switch on the back panel), then take the speakon speaker lead connections out of the failed amp and move them over to the working speakers. Both the tops and the subs have two speakon connectors wired in parallel, so you just take the amp end of the speaker lead for the the non-working top and plug it into the spare connection of the top, and the same for the sub.

Because the impedance of two 8-ohm loads in parallel is 4 ohms, and solid state amps can output more power into a lower resistance, you basically get the same amount of power from one amp as you had from two.

There are benefits to running two amps into 8 ohm loads as opposed to one amp into 4 ohm loads. First, you get stereo, which may or may not be important to you in a gig environment. Secondly the bass response will be a little bit tighter and thirdly the amps are passing 1/2 of the current, so producing less heat and the electronics have a less stressful life.

That last point is a good reason for using 2.5mm2 speaker cables (14AWG) as 1600 watts into 4 ohms is a 20A current.

Just make sure your speaker cables are long enough to stretch between the speakers on a wide stage. If necessary, carry some longer ones as spares. It's always good to have at least one spare speaker lead along with spare mic and jack/jack leads.

If you can, practice setting up the PA like that a few times in rehearsal and if the worst comes to the worst, you should be able to get things up and running again in a couple of minutes.

[Wonks]

There doesn't appear to be any mention of any tweeter overload protection in the documentation for the SRX715 tops.

In passive speakers this protection often takes the form of a light bulb in the tweeter circuit which as the current through it increases, it starts to glow and heat up. As it heats up its resistance increases substantially and limits the current flowing. (In modern powered speakers the protection is normally provided by the DSP which limits the signal going to the inbuilt power amps).

But the documentation for the speakers doesn't mention anything like that, so if running the amps near maximum output, listen to see if the treble is starting to distort and sound rough. If so, back off the volume until the treble sounds smooth again. You can get replacement JBL 2431H compression drivers, but they aren't cheap and you may have to get them from the US where new they seem to be around $330 (so if importing to the UK allow for taxes and shipping on top). There are cheaper Chinese-made alternatives, but I doubt they sound quite the same.

[ef37a]

Re tweeter protection Wonks. Many years ago I had a tweeter pop in a Kef Choral due to 'tape screech' I fitted a fuse holder.

The fusing value needs to be worked up. A 50W 8 Ohm tweeter might seem to need a 2.5A fuse but that would afford virtually no protection at all. I would start at say 315mA and have blast and see the results.

Good point having a trial run. If the OP has nowhere suitable I bet a church hall could be arranged for a couple hours for a small consideration?

Dave.

[Wonks]

But ideally you don’t want a fuse as it’s an immediate sound to no sound change when it works. And if one tweeter fuse goes in a typical ‘dual mono’ PA setup then it’s likely the other fuse goes at the same time and you lose all treble and the gig stops.

The light bulb protection method is better if you can pick a suitable bulb. Basically a fuse in a vacuum, so where a normal fuse gets hot, glows, oxidises and fails almost instantly, the bulb filament glows, heats up but can’t oxidise, so its resistance shoots up and lowers the current flow.

Picking a suitable ‘Goldilocks’ bulb is the issue. Too small and it operates before it should, too big and there’s no protection. Interior car bulbs were the normal favourite selection, but the switch to LEDs has made them hard to get and with a lot less choice than before. Using two or three smaller ones in parallel has become more common with later designs of passive speaker.

(I know fuses and lightbulbs aren't exactly the same apart from the vacuum, as incandescent lightbulbs normally use tungsten filaments which still maintains a lot of strength when heated whilst fuse wire is typically a tin/lead alloy that loses strength quickly and melts at 183°C).

[Hugh Robjohns]

And if one tweeter fuse goes in a typical ‘dual mono’ PA setup then it’s likely the other fuse goes at the same time and you lose all treble and the gig stops.

Well.... you say that...

Long ago I was at a Shakatak gig (remember them?) and part way through the left-hand PA stack on the stage front lost all the top end. The band kept playing but at the end of the number a roady came on and said something to the band members. The band then struck up with another number which featured a bass solo. The bassist was on a radio link and proceeded to move right across the stage to the right-hand side — with his sound following him into the right PA stack. he then climbed down the steps to the floor, and moved part way up the aisle into the audience, all the while playing a very impressive bass solo with a follow-spot focused on him as the only light in the room.

With relative darkness on stage, a bevy of roadies appeared, stripped down the left-hand PA stack, replaced the HF cabinets, and built it all up again. It probably took less than two minutes. The bassist then climbed back onto the stage and moved back to his usual position with the bass sound moving back across the sound stage to match. The rest of the band then joined in and everything was back to normal.

It was a very polished and well-organised recovery from what could have been a disastrous gig, and I bet half the audience didn't even realise what was going on.

[ef37a]

Yes Wonks, as you say a fuse is a S or B solution but I thought finding a suitable lamp might be very difficult?
From a personal point of view, with a crossover at 2.5kHz to the tweeters, if the fuses blew I would not be incommoded in the slightest!

Dave.

[Wonks]

I remember Shakatak.

But you don't know what form of protection, if any, the HF cabinets had. They may have had thermal cutouts, which could be reset once they'd cooled down.

[Sam Spoons]

I've used polyfuses with good results in my passive cabs, overdrive them and they go high resistance and return to very low resistance a short while after the over current is removed.

[Mike Monte]

Fusing:
When I first got into doing sound (early 90's), friends of mine that owned a recording studio used an external inline-fuse when doing live sound.
The fuse "contraption" had one 1/4" female and one 1/4" male "pigtail" connect in-line at the speaker.
I do not remember the details but they used a buss fuse holder:
https://www.grainger.com/product/1CZ42? ... :N:PS:Paid:
GGL:CSM-2295:4P7A1P:20501231&gclid=EAIaIQobChMIl6fK65yu_
QIVUv7ICh0qYQePEAQYFyABEgIpe_D_
BwE&gclsrc=aw.ds

with a fast blowing fuse in a 35mm film canister:
https://www.amazon.com/AKIRO-Canisters-Storage-
Containers-Plastic/dp/B07XXN34JH/ref=asc_df_B07XXN34JH
/?tag=hyprod-20&linkCode=df0&hvadid=416852484227&hvpos
=&hvnetw=g&hvrand=12555441956787643991&hvpone=&hvptwo
=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9002168&hvtargid
=pla-870354734826&psc=1&tag=&ref=&adgrpid=95587149804&hvpone=
&hvptwo=&hvadid=416852484227&hvpos=&hvnetw=g&hvrand=
12555441956787643991&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=
&hvlocphy=
9002168&hvtargid=pla-870354734826
(the cannisters were available for free at local photo shops)

There was a formula they used to determine the amperage of the fuse.

They used them on TOA SL-12 speakers (if I remember correctly).

The guys swore by them.

[Hugh Robjohns]

I remember Shakatak.

But you don't know what form of protection, if any, the HF cabinets had. They may have had thermal cutouts, which could be reset once they'd cooled down.

Indeed... All I can say is that they physically replaced two HF cabs at the top of the PA stack. This was before the days of line arrays and each stack comprised a variety of different sized cabinets for generating bass, midrange and treble noises, with another big box housing large, hot and heavy class-AB power amps.

[Chris__H]

Thanks to everyone for the suggestions and comments. Very informative

In a new post, I am currently researching PA amps to match my cabs in a new post and I'd be keen to get your thoughts on the best amps for the $$$ considering cost, reliability, performance and any comment would be appreciated if you feel inclined. Thanks again ALL

[Chris__H]

Best PA Amp Considerations

https://www.soundonsound.com/forum/view ... hp?t=85638

[ef37a]

Of course you can bypass the fuse with a resistor. For an 8 Ohm tweeter around 16 Ohms 10W would save the drive unit but still allow a bit of HF through.
If you wanted to be really clever fit an LED 'blown fuse' indicator!

Dave.