System setup?

[iksound]

Hi all, I'm curious to know if what I'm doing is right or totally wrong, here goes. am using a 5.5k 3 way opus rig, 4x 1000w 2x 18's, and 2x 750w mid/top's. Opus is made down here in the south west for anyone who isn't familiar with them. they're lovely speakers. (insainly heavy though)

 

what I do is, set my zero db point on the desk meters using the pink noise generator. while the amps are muted. I then go to the crossover and set the volumes on the there. The room in which the system is situated is very toppy. so I've balanced my zero db signal to between -6 and -3 on the crossover. the bass end wont even go that high but is more than loud enough in practice. now, looking at the crossover pot positions, the bass is at +3. the mid at - 2 and the top just above -2.

 

it seems sensible to me to set up a sound system on the crossover like this before touching the graphic. I know they say the proof of the pudding is in the eating, and it sounds great, and I'm not doing much to the graphic. could any of you peeps who have worked on bigger systems tell me, is there a proper scientific way to set up a system. I know a company near me who's method seems to be playing music very loud through the system and turning up the bass mid and top respectively, this doesn't seem right to me.

 

in conclusion, now I know when my desk meters say zero I know I'm close to clipping the amps, which I like to avoid, although they're designed to take it. I always set up my signal inputs to zero, I've been an engineer for quite a while now and I never used to be this paticular, but its working really well for me. so hey.

 

your input is very much appreciated. thank you all.

[Rob_Beech]

Hi Ian,

 

First of all, I'll assume you have the SB218's and CS750's, you don't tell us what crossover you are using or what amps.

I'd probably assume you were using the XS234 controller, but who knows.

 

This to me sounds like an install rig so its important to get it right first off, then you can have years of happy work with the rig. I really like this gear and I do hope you are more than happy with it (you certainly should be).

 

Wherever possible you should have your graphics as flat as possible. the less processing you have to do the better. Digital crossovers (Omnidrive etc) Give you alot more flexibility without the need of any eq FOH. This way you can have your system setup perfectly down by your amps and use your FOH graphic purely to tune a particular show rather than the system.

 

The most important tool for measurement you have in your rig is on the side of your head. There is no substitute for good hearing.

With a digital crossover/processor you should be able to setup the system completely without the need for FOH graphic at all in an install rig. (this doesn't mean you dont need it in the rack).

 

I cannot see any problem with what you are doing, I can't really suggest a better way.

If you have used pink noise to setup the system then this will get you a decent linear response with a bit of tweaking here and there.

 

You also seem to have a decent gain structure where 0db corresponds to 0db. Although you need to remember that when other engineers are using the desk (if they do) they may be inclined to push the desk hard at times. So you need to be careful.

 

All in all, if you are getting a good sound don't worry too much about it.

If you're not however then come back and tell us what you think is wrong and we'll try and help.

 

 

Rob

[iksound]

Thanks very much for that Rob, yes I'm very pleased with the sound, I'm using all opus amps and crossover. I just wanted to re afirm with myself that what I was doing was logical. the thing is if I put all the pots on the crossover to their zero position, the meters don't read zero.

I'm using the XS-234, HD2500 x2. and HD500. controlling 4 sb218's and 2 CS750's. so I think you got it all. sorry. its strange because my own small JBL rig, 3.5K, I have a DBX 234XL crossover and I have all the outputs set to their zero points??? and its balanced. can you explain why zero seems to differ so greatly. or am I missing something. if you get to a large, say, glastonbury sized rig, where do you start? is a lot of it manufacturer specified?

thanks.

[Simon Lewis]

Bear in mind that if you adjust the crossover levels too far from zero, you will alter the acoustic crossover frequency.

 

Simon

[iksound]

thanks Simon, I didn't know that but I'm afraid I don't understand how that works, could you elaborate that for me please?

 

cheers

[J Pearce]

I may be wrong but I think Simon means that if one dropoff slope starts a lot higher than the other then the point that they cross at will be skewed to the side of the higher slope. As the point at which they cross is the perceived crossover frequency, this will alter the perceived crossover frequency.

 

Hope that makes sense, it is hard to describe in words.

[RonJon]

Here's my two pence, after ten years of install/comisioning and systems on some big events, I would suggests an alternative o the 0db route, and the way that I may set systems up for the absolute best dynamic range, and therfore lowest audible noise floor, is to set everything up to the peak point of the equipment used. So for example, get your refernece tone out of the desk, *remember to up from a 1khz tone to 8khz when linning up the hf amp, and drop to 80hz for the sub* and wind the output signal up to the point that the peak lamp just comes on, then any in line processing, and finally the amps, its best to set the mids first, then the HF, as the HF normally gets a lower input signal than the mids. With your subs running from an aux, do the same procedure along the line from the aux out, to the amplifier and so on. I would recomend that the graphics are inserted into the desk (if your useing them) in preference to running them in-line.

 

I know that this is a slightly un-orthodox way of doing it, however, if your leaving the system to other engineers to mix on, they will not blow any of your gear, as a lot of engineers I have encountered mixing on small rigs mix to the needles, not their ears, so it can sound to loud. And if your doing anything where you need th PA to be un-notiable, ie a classical event, then this should make your speakers disapear, insofar as amp-hiss is concerned. It is ideal for theatre systems, especially where the pa is quite for long periods of time. You do NOT lose any useable level availible in the system, just the last few dB where the amps and processors are clipping to the nines, and eberybodies ears hurt.

 

With regard the shifting crossover points are concerned, if you are useing the recommended amplifiers, and a system controller, then it shouldn't be a problem, and can almost be forgotten about, as everything should fall at the right level. If you are running your system through a DSP, such as a Soundweb, and a controllable crossover, then you should be able to sort out the difference with some subtle tweaks in the web. Though smartt will make this a whole lot easier(or should I say quicker), especially with regard to phase response, which is the biggest killer of cross-over frequencies, you can do it by ear... but it's not fun ** laughs out loud **. I would say, that if theres more than a couple of dB difference in the level of each amp, however, then you may need to change the amps.

 

Hope this is of some use.

[Simon Lewis]

Re: shift in acoustic crossover point:

 

If you (say) boost the level of the bass output at the crossover, then the LF pass band is effectively rasied with respect to the HF pass band, and consequently the effective crossover point of the LF device is increased.

The Meyer Sound handbook gives some good information on this.

 

Re: Ronjon's comments:

 

This is the practice of achieving correct gain structure, and you can take it beyond what you have described. Have a look at the Study Hall at the Live Audio Board - several very good articles there (hope it's OK to cross reference!).

[iksound]

Thanks for that guys, I now have a lot to think about. I know its hard to describe things like this just using text. I guess we'd all benefit from some sort of mad scribble pad. but I appreciate your input. no pun intended.

 

all in all at the moment, the system sounds nice, and I'm the only engineer that uses my gear, the one problem I have in the room is keeping the volume of the band on stage down so I can get the vocals out. I'm fairly tough with the bands, (especially the guitarists) who are all very proud of their 4x 12 Marshall cabs, that are way over sized for the room. and the drum cymbals that take over everything.

 

just going back to your comments ronjon, my desk is an Allen and heath GL2200 and it only has 1k or pink noise. if I've read your method correctly, then am I setting my desk output to its max to ensure that the amps will never peak? also what then do I do with the outputs on my graphics?

 

how do I run the subs from the aux? does each channel have to be set separately according to weather it needs much bass or not. sorry if I'm sounding a little confused...!

 

thanks again in advance.

[RonJon]

Ian,

 

In response to the first question, if you set the desk out to max, I find the best place to put graphics is in the main inserts of the desk. This has the advantage of it being configured to run at +4dBu and you shouldn't have to worry about lining it up with the rest of the system, and the other bonus is, the desk will do the hard bit of driving the bits of cable to the amps/controllers/dsp's at the amp end. If you can find an alternative source of tone, for lining up HF and sub, then all for the better, should be able to get them from the internet, have seen a few freeware tone generators, which should be acurate enough for the time being.

 

The main idea behind setting everything to the desks max output, and maybe a tidge back from it, is, as you summised, to make sure that nothing else in the chain will clip, meaing that the only place that you are ever likely to clip is at the desk end, and the clip lights normally come on way before actual clipping takes place, Q.E.D. a completly bomb proof system, with the largest possible dynamic range, lowest noise floor, and smoothest operation, as all the faders will end up around the 0dB mark if you set the input gains correctly too. I'm lazy, so find that the extra work now, makes my life easier on. :0)

 

With regard to the "Sub off an Aux"; the main theory behind this is, most of the time you don't want to have voice, electric guitars and most stuff going to a big pair of bins, as this is what tends to make a system sound muddy, and the subs loose their attatck. I would normally put a lot of Kick, though it's the low mids that give you the thump in the chest, into the subs, to make trousers shake, Bass Di, though not Bass Mic, maybe floor tom, and keyboards, lots if they're being used for pads. Experiment, but doing this will mean that it is possible to get a far tighter sound from a given PA. It becomes second nature, but remember to put the aux outs into post fade mode, or you can get the odd suprise.

 

Feel free to get in touch directly if you want to go through anything directly.

 

Just a quick response to simon whilst I'm typing,

 

RE: Quote: "If you (say) boost the level of the bass output at the crossover, then the LF pass band is effectively rasied with respect to the HF pass band, and consequently the effective crossover point of the LF device is increased."

 

I would always recomend reducing relative levels, in stead of boosting, unless you HAVE to, as it can affect gain structure, noise floor, and create problems with Limiting/Clipping in real world situations, though views from others would be appreciated.

 

Appologies for the long posts, not very good at condensing information....

[Simon Lewis]

RonJon,

 

Neither would I recommend boosting a crossover passband, but I used it as an example to show what can happen.

 

The perfectly flat and well behaved crossover characteristics shown in teh LCD of most loudspeaker management devices does not actually translate into an equally flat acoustic response ;-)

 

 

Simon

[iksound]

thanks again guys, that's helped make things clearer ronjon cheers, I may well get in touch. To run the subs from an aux, do I then need another crossover, obviously putting highs into a sub is the quickest way to making the worlds largest paper weights. ** laughs out loud **: but seriously, I've only got the one crossover. I've also got BSS OPAL 966 graphics? would it be feasible to cut everything but the lower registers out of those to feed the sub amps? or do I need a second crossover.

[Rob_Beech]

Hi Ian.

 

For this you would certainly need some type of crossover for a Low Pass Filter for your subs.

This could be don with an analogue crossover just using the low outputs.

A loudspeaker management unit. You could even run the whole system from this if it has 3 inputs.

If you currently have a graphic with a variable LPF built in it may be possible to use that. Although its possible that the LPF wont go down far enough.

 

 

Rob

[iksound]

Thanks rob, just going over the point of running everything to nearly max output, I think if I did that then I wouldn't be able to get the input level, or the output levels down low enough, I'm sure its possible with a digital loudspeaker management system, but on an analogue crossover, won't it just mean that the gain structure is out of kilter because the output pots are too far from zero, for those people who aren't familiar with opus, there's no input volume control. sorry to keep asking awkward questions.

 

thanks to all who have and do respond. I really appreciate it.

[iksound]

thanks to all participants in this discussion. cheers guys. and thanks to theblueroom THANK YOU.