Gain structure question

rickrock

Posted the following at the Lab, and first response was a poster telling me to shout out to Gadget in this forum. The link is here to read the thread:

http://srforums.prosoundweb.com/index.php/t/30974/0/.

I know I'm not a pro at this, but I'm trainable. I felt like my post there died because the guru's deemed me hopeless. Any help would be appreciated. The last post of mine in the link is the one that I need answered.

Any help?

much obliged
rickrock

Dra

I tri amp now, all set at 1.4v, all fed through the same 260 dsp, so that would suggest the same gain structure across all three frequency bands.

That would assume that all the amps were perfectly matched to the drivers efficiencies and output requirements, and there is no such thing, since frequency bands require different headroom levels. That is why we always recommend manually setting gains and then tuning by ear. There is a good walkthough of this proccess in the READ ME FIRST section. Kevin, Gadget, and I all contributed to this document.
I also am eager to hear Gadget's answer.

DRA

rickrock

You must mean the long one about setting up gain structure, downloading the pink noise sample etc. (at least I think I found what you referred me to). Excellent help. Doesn't quite get to the question though.

I also have only now begun to figure out how the GUI software works. I have it on this computer, but I need to get my computer to see the 260, which it doesn't yet. I put in all the parameters in the wizard in the software, and voila! same thing, all the CX gains were set down around -11 or -15 db. The jbl publication shows for me +4.3 on the subs, 0 for the mids and -10 for the horns.

Dra

I wonder if JBL is assuming that all the amps to the three components are the identical. That would acount for the increase in the sub and decrease in the horn.
For all the filters to be cut implies, to me at least, that it must be a S/N thing. That same (similar) issue came up on the board within the last week or so. Whether to set the 260 at -0- and turn down the amps or visa-versa or in the middle some where. We never came to a solid conclusion.
I know this does not answer your \"technical\" question. These \"mathmatical\" questions are the kinds of things that PSW excells at (even though they argue back and forth on things like this and you never know who to believe). Unfortunately they sent you here.
Maybe Gadget can shed some light soon.

DRA

Dra

Just went in and played with your config. Changing amps, unbridging the sub amp, passive tops, bi-amp with no sub, etc. The Xover gains change dramatically. Some of the problem could be that the DR's do not give the option for bridging on anything except a \"sub\". Play with it and see what I mean.

DRA

rickrock

You have to believe when the wizard asks you to ID the amp, then tells you where to put the pot, it knows what the output is into your chosen drivers. And it asks for all three band widths. I already \"fool\" the wizard by telling it I use the xti 4000 for the mids, when what i really have is a bridged xti2000. But because we can program without the wizard through the GUI software, I'd like to be more precise. But I understand your point about the assumptions in the jbl parameter chart, they could be assuming same power into all three bands, it doesn't tell you how they're powering the speakers in the chart.

Nevertheless, fooling the wizard to get to the right CX gain setting is what I'm seeking to avoid. There were some posters in the PSW post that suggested flatten the 260 and use the amp attenuators, but that seems unsafe, esp. when the wizard is telling me to cut so much. And those srx700's are power hungry, they will take more power than I'm giving. The horns are program 100, they're getting 275. The mids are program 1200, they're getting 2000. The subs, 2x18 = 4 ohm load, with a bridged ce4000, are program 1600, getting 2400. The horns are a little hot, but the rest are comfortably within normal overpowering standards. So why so much cut from the wiz?

When you put in my equipment specs, did you get the same CX gain cut? In any event, thank you for your input, I appreciate your time and interest.

much obliged
rickrock

Dra

Yes, I did get huge cuts in the X-over. But when I unbridged the CE4000 the sub gain jumped to near -0-. What I wish I knew for a fact was where the wizard data came from... Some guy maually (trial and error) setting all the params or a guy with a calculator crunching numbers, or both.

Good luck.

DRA

Just had a thought. Maybe the gains are cut so much, because the wixard is looking at the gain potential to the amp into the driver rating and is compensating. :? Got me.

Gadget

Number crunchers...

In order for the AMPS input sensitivity to be useful the gain of the crossover would have to be modified to suit...

Seems to me like too much of a compromise, and our gain structure becomes more difficult...

Gary

rickrock

Mr. Gadget sir, I wish like heck I understood that, but you lost me.

I'll just say I sized my amps appropriately, keep all amp sensitivities at 1.4v, I set the amp attenuators where the wiz tells me, and the sound is anemic I have excellent equipment, all made by the Harmon family. And it seems it is due to the CX gain reductions. I'd like to think if the wiz puts them all at -14 db or so, that if I raise them all about the same in relation to each other, say raise each by 5 db, that this would work, and I would not blow up the speakers. It's either that or turn up the amp pots.

Is there no rule of thumb here? I'd love to know the science too, but at the moment I'd be happy with a reasonable solution.

much obliged.
rickrock

Dra

By anemic, do you mean low volume (but accurate)?, no impact (lifeless)?, what.
Check to make sure the PEQ's are on.
What are your limiters doing?
What are your output meters doing on your board?
What are your input and output meters doing on the 260?

Have you gone straight passive from the board?
Have you biamped using the amps DSP only?

DRA

Gadget

I don't know how I missed this thread... well I guess I do.. I'm preoccupied with WOMEN! That was a nice thing they said about me over at the PSW...Anyway see if this makes any sense:

http://www.driverack.com/drug/view_thre ... d_id=40803

And this...:

http://www.driverack.com/drug/view_thre ... d_id=40802

I'll try and review this subject at my earliest convenience.. but right now I have women to deal with... 8) and work.. LOTS AND LOTS of it...

G :roll:

rickrock

By anemic, do you mean low volume (but accurate)?, no impact (lifeless)?, what.
Check to make sure the PEQ's are on.
What are your limiters doing?
What are your output meters doing on your board?
What are your input and output meters doing on the 260?

Have you gone straight passive from the board?
Have you biamped using the amps DSP only?

DRA

I mean low volume but accurate, no impact.
PEQ's have definitely been on, but that's a good checklist item
Don't know what the limiters are doing, but they are set at +18
Output meters on boards are bouncing over 0db, not getting into red (just stereo meters, mackie 24-4vlz board)
Input and output meters on the 260 are hardly getting out of bed, very little movement, like up 3-4 bars, 1/3 the way up at most (as I recall, we don't use it for practices, only gigs, so I need to watch during a gig with the whole band mic'd up).

The last two suggestions are trouble shoots that I have not done. I try to steer clear of the xti DSP's, and just keep them manual and use the 260. Not sure what \"straight passive from the board means\", unless it means leave the subs out, switch the 722's to passive, and don't use the 260. But I those are last resorts. I'll read the posts Gadget posted, between women, and then circle back.

thanks so much for your input and advice
rickrock

Dra

Your 260 input meters should mimic your board output meters. Your 260 output meters should mimic your 260 input meters.
You say your 260 input meters are well below the meters on your board. Open up the input mixers in the 260 and increase the gains (should default to -0-) until the meters match.
That has to be it, but not sure why you would have to do that.

DRA

Gadget

Kinda depends on the crossover gains also...If they were way down you might have to add gain @ the output mixers.. but just make sure that the crossover gains are around zero to start... unless your using the amps \"input\" sensitivity and setting the 260's internal gains to match them...

Also the meter ballistics are much slower on the front panel than the GUI ... I would believe the GUI before the \"L E D's\" on the front panel...

I realize you would like to understand the dynamics of this whole issue, but seriously, we have been playing with this for some time now and if you follow the \"gain structure\" tutorial in the \"welcome\" post you should have a wonderful rich system that is punchy and quiet... The input sensitivity just complicates the issue because of various amps, various speakers and nothing matched.. kinda real world versus 'Idea\", l add the \"new indoor method\" to your tops for a flat system response, make sure all components are working together.. I.E. with a positive 9v to the plus and a negative 9 volts on the minus that all cone drivers go in the same direction ...

Gadget

rickrock

Kinda depends on the crossover gains also...If they were way down you might have to add gain @ the output mixers.. but just make sure that the crossover gains are around zero to start... unless your using the amps \"input\" sensitivity and setting the 260's internal gains to match them...

The above gets so close to answering my question. As it \"depends\" on the CX gains, let's start with a given: the 260 reduces the CX gains substantially, 8 to 10db, when loading the speakers/amps I program. I am only telling the 260 what my input sensitivity is set (and then only for the sub amp) but they are all set at 1.4v. So I'm not \"using\" the amp sensitivity in any active way to modify the sound, I'm only telling the 260 where the amps are at.

So, that said, (and assuming my gain structure is otherwise tuned as per the tutorial), when you say, \"make sure the crossover gains are around zero to start\", that has to mean :

1. AFTER the wizard has already squashed the CX gains by loading my program,
2. I manually set the CX gain settings all back to 0db,
3. I leave the amp attentuators where the wiz told me (in my case around 12:30 or 55%)
4. I tweak the 260 input mixer to the three 260 bands up or down to get balanced sound by ear; and last
5. I boost the mixer output mix (over unity gain) during sound check, and on the fly during the gig, as needed to add overall gain

If the above is correct procedure, I have the answer I have been seeking.

Dra

It sounds as though you have not gone in and looked at the input mixer.

I tweak the 260 input mixer to the three 260 bands up or down to get balanced sound by ear; and last

The input mixer is simply another master fader (gain manipulator) between the board and the DR. It controls all \"bands\" together because it only sees the \"mix\" entering the DR.
Pink noise source
Board Meters @ -0-
260 input meters @ -0-
All 260 output meters @ -0-
I would probably ignore everything the wizard says except for the X-over point / slopes and the PEQ info.

DRA

rickrock

Not quite, although neither my 260 nor my software are here at work. I looked at the software last night and wrote the preceding post this morning. My memory was that there was an input for each band, but now that I think about it, there were only two, stereo, from the right and left inputs. In that regard, thank you for your gentle reply :oops:

I get your gain structure shorthand, which I understand to be the goal for setting up the gain structure with the pink noise cd, but for one point: with all the other settings (in your last reply) at 0db, leave the CX gain for the three bands where the wiz puts it, (because I'm tuning to get 0db at the 260 output meters with the CX gain at the point the 260 prescribes) or manually put that at 0db with the rest? OH OH, maybe this is it

---

that is what I'm adjusting to MAKE the 260 output bands READ at 0db---that's got to be it.

much obliged
rickrock

Dra

I will assume that if you get the the input meters to match the meters on your board the wizard may be right from that point because it's factoring the amps and the driver sensitivities, etc. However, it still seems odd that all bands are cut so much. I bet it is limiting the output of the amp to program power rating of the speakers (ie: \"Those speakers need 400 watts. They are using an 800 watt amp. We need to limit the amps output to 400 watts. We can do that by lowering the gain into the amp at the x-over and setting the limiters.\") instead of 1.5x or greater as most practicers espouse. I would wager that if you raised the highest band level to -0- and kept the db difference the same to the other 2 bands, that would be kicking.
Gadget? Am I out of line here?

Definitely let us know how it goes


DRA

rickrock

Excellent, will do, and thanks again. One last question. I could not get that website with the pink noise 20 min. download to produce a good (uncorrupted) file. Who has a good website purchase point to sell one they will mail me?

Rickrock

Dra

Google it. Bound to be plenty. Or contact Bink.

DRA

rickrock

Went back to HC and started the following thread, and I'm still a little lost. If you read, you'll see how I am trying to get my gain structure correct, using info learned from the 260 manual plus THIS thread here at the dbx forum. I'm being advised over in HC that something's wrong with my approach, particularly regarding the limiter settings, and I'd much appreciate clarification.

http://acapella.harmony-central.com/for ... ?t=1920106

As we discussed here, I'm setting my meter levels to 0db with pink noise at the mixer, adjusting the 260 (in and out) to read at 0 db, with the 0db pink noise signal from the mixer. Then I take that 0db signal from the 260 to the (unloaded) amps, and increase the amp pots till they clip, then turn on the 260 limiter, and back it down till the amps stop clipping. That leaves the limiter at about 16db, and the amps at about 3 o'clock. I then put the amps back to where the 260 told me for each band, around 1 o'clock. By the way, with the 260 input meters at 0db, to get all three output band meters in the 260 to read at 0db, I need to adjust the 260 crossover gains, typically up over 0db to 3-6db.

Where am I going wrong?

BTW BIG GIG TOMORROW 3/15--REPLY TODAY WOULD BE VERY VALUABLE.

Thanks so much.

Rickrock

Dra

Your desciption is very helpful. Here is the problem... you have set every to -0- and to have you amps clip at that point. That is not a good idea. After setting the everything but the amps to -0-, you should then push the master faders up into the (top) red on the meters. Now make sure that the input meters of the 260 (best to use the GUI) are 4-6db below clip. Then check the output meter (same). Next do the amps to clip. Next set the limiters. Then turn back the amp a tad.

DRA

rickrock

Okay, so by \"setting everything but the amps to 0\", you mean do it this way.

1. Generate pink noise to mixer, set channel faders to unity, set submaster at unity, set mains at unity, solo and trim channels to which the pink noise is input to get 0db meters; take off solo, raise mains to get back to 0db meters
2. Set 260 input gain to 0, check 260 meters, if not at 0, adjust 260 input gain slightly to get to 0db
3. Set all 260 crossover gains to 0db
4. Turn off 260 limiter
5. Set amp pots to level dictated by 260 presets, approx. 55%
6. Raise mixer mains to clip mixer
7. Adjust 260 input gain so input meters show 4-6 db below clip (mixer meters still show peaking)
8. Adjust all three bands of crossover gains so all three pair of output meters show 4-6 db below clip (mixer meters still show peaking)
9. Crank amp pots till the amps clip lights go on
10. Back down the 260 limiter till the amp clip lights go off
11. Back the amp pots down slightly from the clip level (or back to 55% or not?)
12. Back mixer mains down to 0db, to taste, to what suits the rooom and the gig, etc.

Have I got it right now?
much obliged
rickrock

Dra

#5 is not neccessary. Try to forget that you ever saw the 55% in the wizard. You can use it as a comparison to what you end up with, but other than that forget it.

#9 takes the place of #5. You can start at 55%, but regardless your going to turn the knob.

Add #10A - Turn limiter \"Off\"

change #11 - Turn down amps until no clipping ( or maybe an occasional lighting)

Add #11A - Turn limiter \"On\"


DRA

rickrock

Very helpful, I get it. Wish me luck, I'll report back, thanks.
Rickrock

rickrock

Well thanks to all. I was under the gun to get the system tuned up for a big gig last night. I set up the gain structure Friday night, using the \"12db below clipping\" standard, rather than 4-6db, based on agedhorse's suggestion in HC. Comments on that are welcome, but for what it's worth.......

It sounded great. We had the added benefit of having a warm up act, so I could tune the system even better.

Interestingly, after setting everything to 0db with the pink noise, and raising the gain on the mixer to approx 10db. I needed to lower the input gain on the 260 to -4db to get the meters to 12db under clip. From there the output needed the mids and subs notched up +4db, the highs at 0 to get the output meters to the same point. The amp pots ended up around 2:30, and the limiter ended up somewhere down around +8 (not sure, but it was much less than the +16 I got the first time around).

System was plenty loud for the room (which had a capacity of 400-500) and had headroom to spare. Only funny thing about the Mackie mixer is for the pink noise to be set at 12db below clip, there's only one yellow caution light at I think 10db, and the next LED is a single red clip light all the way at 28db (!?!). So I just pushed the pink noise a little ways into the yellow light and went from there. I suppose I could have pushed the mains to mixer clip and backed off slightly from there, but I went the other direction, just raising it enough to make the 10db yellow solid, up from the last green LED.

The only thing I'd like to have done is used the GUI from the 260 software rather than the front panel meters to set this all up, but no matter what I try, i cannot get this darn laptop to see the 260 when I hook it up. I can interact with the software on the laptop fine, I just can't get it to see the 260. Now, I did have to buy an adaptor cord (pins to USB) to get the 260 to even connect, and the computer seems to know something new is hooked up, but...anyway, I'm not getting the perfection I could be if I used the GUI now that I understand this, but I'm a heck of a lot closer.

Thanks for all your help.
rickrock

Gadget

The laptop doesn't have a \"serial\" port then... just a USB port and you need a usb to serial adaptor... see the \"read me first before posting for the approved adapters...

Thats fine what you did but you still don't know where the \"system\" actually clips without hitting the clip slightly on the mixer. !2db of headroom is great.. if you can get away with it...I prefer that also...

Glad it worked out... keep on learning, and reading... I'm sure there's more you can squeeze out of your system...
gadget