Question on Gain Structure, X-over Gain and Limiter Settings
Rikkimax
Posts: 14
Hi,
I have a few questions for your expert consideration regarding gain structure, crossover gain and limiter settings for the DRPA.
FYI, I have read the manual, the FAQ, and many of the forum entries on these topics. There are a few variances between these sources of info, and a couple of things are not clear to me at this time.
My equipment is as follows:
Allen and Heath Mixwizard 16:2
DRPA
Pair of JBL SRX712m (tops – passive - stereo)
Pair of JBL VRX915s (subs - stereo)
Pair of QSC PL-236 amplifiers (each in mono – left and right for the tops)
QSC PLX3602 (in stereo for the subs)
I used the DRPA configuration wizard to set up the parameters for all the speakers and the sub amp. I used “custom� setting for the top amplifiers, as they were not listed in the wizard. Overall, the system configuration is a stereo tops and stereo subs (2x4).
I carried out the following steps in setting up the gain structure:
Put pink noise into an input channel and used PFL to set the channel gain to +6 db max.
Turned off PFL, and pushed the LR main faders up until they showed clipping, and then backed them off a bit until no clipping was apparent, and the overall mixer main output level was about +6 to +9 db. HERE IS MY FIRST QUESTION: The manual says to push the mixer Main LR faders up to clipping, and then back them down a little until clipping goes away. The gain structure FAQ (which mentions the user interface, which I don’t have), seems to state that I should put the mixer LR master levels to unity 0db before proceeding with the rest of the gain structure setup. Is this the case? Where should the mixer main LR output be reading before moving forward with the gain structure setup process?
At this point (with the mixer main LR output level below clipping, and peaking at about +9), the DRPA input level looked very healthy, with no clipping, and the levels bouncing in the yellow at +15 db. The DRPA Hi Output levels were also very healthy, with no clipping, and the levels bouncing in the yellow at +15. HOWEVER, the Lo Output levels on the DRPA were very weak by comparison, barely bouncing at 0 db and only very occasionally at +5 db. Additionally, I could just barely make my sub amp go into very light clipping at this point, even though the amp attenuators were at max. HERE IS MY SECOND QUESTION: Should I go ahead and increase the gain of the Lo band of my DRPA crossover to try to get the Lo output level a bit more healthy? I know that this is the digital domain, and the gain is not as critical, but this just seems too low to me. Will I wreak havoc with the crossover transition zone if I change the gain in this way? I was planning on using the amp attenuators to set the final balance between Lo and Hi in the end anyway…
Finally, I followed the instructions in the FAQ regarding limiter setup. First off, I believe the FAQ indicated that you should use Overeasy 4 as a starting point setting, but one DBX link in the Forum says that overeasy should be set to “off� during the limiter set up process. At any rate, I used Overeasy 4, as the wizard chooses that setting (with a threshold of +18db) for the QSC PLX 3602. Also, the DBX link states that the limiter threshold lights should only very occasionally illuminate during hard peaks. I found that the limiter threshold lights actually flashed quite a bit, even when not being driven hard, and when the threshold was set at +18 db. Strangely enough, the limiter threshold lights even flashed with my very low LO output band readings on the DRPA (i.e. around +5 max)! Is it flashing because of the overeasy setting? I tried turning the overeasy off, and it still flashed what I feel was prematurely.
Your thoughts and suggestions would be most appreciated. Best regards!
I have a few questions for your expert consideration regarding gain structure, crossover gain and limiter settings for the DRPA.
FYI, I have read the manual, the FAQ, and many of the forum entries on these topics. There are a few variances between these sources of info, and a couple of things are not clear to me at this time.
My equipment is as follows:
Allen and Heath Mixwizard 16:2
DRPA
Pair of JBL SRX712m (tops – passive - stereo)
Pair of JBL VRX915s (subs - stereo)
Pair of QSC PL-236 amplifiers (each in mono – left and right for the tops)
QSC PLX3602 (in stereo for the subs)
I used the DRPA configuration wizard to set up the parameters for all the speakers and the sub amp. I used “custom� setting for the top amplifiers, as they were not listed in the wizard. Overall, the system configuration is a stereo tops and stereo subs (2x4).
I carried out the following steps in setting up the gain structure:
Put pink noise into an input channel and used PFL to set the channel gain to +6 db max.
Turned off PFL, and pushed the LR main faders up until they showed clipping, and then backed them off a bit until no clipping was apparent, and the overall mixer main output level was about +6 to +9 db. HERE IS MY FIRST QUESTION: The manual says to push the mixer Main LR faders up to clipping, and then back them down a little until clipping goes away. The gain structure FAQ (which mentions the user interface, which I don’t have), seems to state that I should put the mixer LR master levels to unity 0db before proceeding with the rest of the gain structure setup. Is this the case? Where should the mixer main LR output be reading before moving forward with the gain structure setup process?
At this point (with the mixer main LR output level below clipping, and peaking at about +9), the DRPA input level looked very healthy, with no clipping, and the levels bouncing in the yellow at +15 db. The DRPA Hi Output levels were also very healthy, with no clipping, and the levels bouncing in the yellow at +15. HOWEVER, the Lo Output levels on the DRPA were very weak by comparison, barely bouncing at 0 db and only very occasionally at +5 db. Additionally, I could just barely make my sub amp go into very light clipping at this point, even though the amp attenuators were at max. HERE IS MY SECOND QUESTION: Should I go ahead and increase the gain of the Lo band of my DRPA crossover to try to get the Lo output level a bit more healthy? I know that this is the digital domain, and the gain is not as critical, but this just seems too low to me. Will I wreak havoc with the crossover transition zone if I change the gain in this way? I was planning on using the amp attenuators to set the final balance between Lo and Hi in the end anyway…
Finally, I followed the instructions in the FAQ regarding limiter setup. First off, I believe the FAQ indicated that you should use Overeasy 4 as a starting point setting, but one DBX link in the Forum says that overeasy should be set to “off� during the limiter set up process. At any rate, I used Overeasy 4, as the wizard chooses that setting (with a threshold of +18db) for the QSC PLX 3602. Also, the DBX link states that the limiter threshold lights should only very occasionally illuminate during hard peaks. I found that the limiter threshold lights actually flashed quite a bit, even when not being driven hard, and when the threshold was set at +18 db. Strangely enough, the limiter threshold lights even flashed with my very low LO output band readings on the DRPA (i.e. around +5 max)! Is it flashing because of the overeasy setting? I tried turning the overeasy off, and it still flashed what I feel was prematurely.
Your thoughts and suggestions would be most appreciated. Best regards!
0
Comments
DRA
Gain structure should be set with meters at -0-, then bring up the amps until they peak, then a hair down.
Limiter settings with mixer meters in the red.
DRA
Also, on the limiter set-up, the forum's "read me first" section (copied below) indicates that after setting gain structure that I should turn the AMPS back up to clipping, and then reduce them via the limiter...it doesn't mention increasing the mixer level to clipping...Please let me know your thoughts on this.
A. Determine the clip point of all amps by setting the gain structure.
B. After turning down the amp and marking the point where the amp stops clipping, turn the amp up to where it clips again. C. Press the \"Comp / Limiter\" button 2 times to get to the Limiter section.
D. There is a limiter for each x-over section that it set up. For example: 2-way (Hi and lo) has 2 limiters, 3-way (hi, mid, & lo) has 3 limiters. Select the section that needs to be limited (all need to be limited).
E. For the selected output, select Over Easy as on. This gives a softer, less noticeable limiting effect. Select setting 4 as a starting point.
F. Lower the threshold until the amp stops clipping.
G. Return the amp to the previously marked spot.
H. Repeat steps E - G for all output bands.
The FAQ process assumes that the mixer is peaking (I am pretty sure it says so). The whole point is that the amps CAN'T clip, even if the mixer is.
DRA
for instance, in my three way system I have a sub that's 95 db efficient (1 meter 1 watt), and my mids are 98 db efficient, and my horns are 107 Db efficient...I will leave the mids @ -0- db and raise the subs to +3 and lower the horns gain by 9db...
Remember that in changing the "electrical" crossover point, you are changing the electrical and acoustic xover points as well.
Gadget
Your subs are your least efficient, and most power hungry speakers... so it is not unusual that they would be low...
G
BTW it may not seem intuitive, but moving the gain control on the amps ALSO varies the crossover point...
You are certainly right: My subs are the least efficient and most power hungry, that is why I would expect that the gain on my DRPA Lo outputs would automatically be set higher right from the wizard. My guess is that the Lo band is producing a relatively narrow frequency band (only about 41 Hz to about 90 Hz), and that is why it is not showing more activity, even when pinked.
Normally, since there are so many variables, you will not see ANY manufacturer provide crossover or gain info on speakers that are not bi-ampable, or tri-ampable and so on... Passive speakers just don't normally have any settings, because they could be matched with too many variables... like what amps? what subs? what tops? JBL is a Harmon company like DBX and they still pretty much supply info only for passive speakers with bi/tri/amp capability and active speakers...
So no if you get a setting it's provided by the MFG or left @ -0-... for the most part.
You see, you could have a pair of Peavey SP218 subs and one guy has a RMX2450 giving them only about 1200 watts per sub ( 600 watts per driver) and someone else using a Digam K10 with 4000 watts per speaker too many variables...
Gadget