• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Is this a reasonable way to set up my PA?

Rockin Mike

Rockin Mike

May 27, 2011
2,772
424
#1
I'm not experienced with live sound reinforcement so I want to take advantage of the automation in the dbx DriveRack PX to get good sound coming out of the mains and monitors.

I have:
1. Allen & Heath MixWiz 16
2. dbx DriveRack PX
3. QSC K Series, 2 mains and 1 sub
4. Mackie Thump, 3 used as floor monitors.
5. Not enough money to buy any more gear, and not willing to put more money into it before learning how to use what I've got.

First I did the obvious thing, going stereo from the mixer into the dbx and setting it up for stereo mains with 1 sub, and running each monitor on its own separate aux straight from the board. That sounds pretty good to my untrained ear, but the only tools I have to get rid of feedback in the monitors are the 3-band EQ on the monitors themselves. I'm not sure if the auxes are post-EQ, but I think they are not.

Now I'm thinking about the following, and would appreciate any experienced advice about whether it's a reasonable approach:
Mono out of the mixer into the left side of the dbx, and from there into the mains.
aux1 out of the mixer into the right side of the dbx, and from there into the daisy-chained monitors.
aux2 into the sub
I figure this way I can use the dbx to automatically set a decent monitor mix as well as the main mix, and I can limit the sub sources to just the kick drum and bass guitar.

good idea? bad idea?

Thanks!
 
#2
Why not run the sub out off one of the channels on the DBX? That way everything is in the full mix and you have proper separation of your freqs. You'll still have full main and monitor EQ control (assuming I have a full understanding of the DBX controls).

Subwoofer frequencies should go to the sub, regardless of the instrument they come from, IMO. If an instrument doesn't produce subwoofer frequencies, then it doesn't matter if it is in the sub mix or not.
 
#3
Your original set-up sounds good to me but I would rephrase the question to ask "what's the most practical way to squash monitor feedback?" FTR, dual channel GEQ's and multi-band PEQ's can be had for cheap and quite effective when placed between the aux outs and powered monitors. Per the suggestions of others, I'd go with a GEQ as its easier / quicker to hit a slider in a "rescue" situation than it is to dial out the offending freqs with a parametric.

Riis
 
#4
I had read some discussion that it's good run the subwoofers off an aux from the board so you can control what instruments go into them. This approach uses the sub's internal crossover. Another way is to put the LR full-range outputs from the board into the dbx and let its internal crossover send the right frequencies to the sub. Looks like there are two schools of thought. Pros and cons that I can think of are,

1. The sub's internal crossover is certain to be tuned right for the cabinet. I don't know how to tell if the dbx's crossover is right for the sub. It has presets for QSC Ksub and K12, but I would have to trust that they're implemented correctly. I guess if the dbx crossover is too high it's no problem as the sub would just give the signal any needed haircut, but if the dbx crossover is too low it would create a hole at the bottom of the low mids which would suck the punch right out.
2. Feeding the subs from the dbx would take advantage of automatic feedback suppression (AFS) any other signal grooming. Do subs commonly feed back?
4. Some folks say lows from vocals and guitars muddy the sub mix so it's good to feed the subs from an aux so you can exclude them and tighten up the low frequencies.

I guess the thing to do is try it both ways and see if there's an audible difference. This may vary with the room, though, so if anyone has experience doing it both ways I'd love to hear about it.

The dbx has left and right outputs for the mains, and left and right outputs for the subs. I only have one sub. I could set it up so the left main out goes to the (mono) mains, and the right main out goes to the (mono) monitors, and the left sub out goes to the sub.

I think running the dbx with left->mains and right->monitors is a winner because then I can take advantage of the automatic feedback suppression (AFS), compression, auto-leveling etc. for both mains and monitors. I'm wondering if I also need a dual 31-band for feedback "rescue" or whether the AFS can handle the whole job all night. AFS has 12 notch filters (per channel I think for a total of 24). By default 6 are fixed frequency meaning they are set when you ring out the system with the RTA mic and the setup wizard, and 6 are "Live" meaning the thing dynamically sets them as needed during the night. Might not need a separate GEQ. Probably worth giving the dbx a chance before spending any more money.

Thanks for the advice!
 
#6
KingRazor said:
At my church we used to run all channels to all speakers, but we had an issue where when the Pastor would walk by the sub, his mic would feedback. Once we started aux feeding the sub with only bass and kick we never had feedback issues again.
Click to expand...

That is a good thought. An ounce of prevention is worth a pound of cure, they say.
 
#7
KingRazor said:
At my church we used to run all channels to all speakers, but we had an issue where when the Pastor would walk by the sub, his mic would feedback. Once we started aux feeding the sub with only bass and kick we never had feedback issues again.
Click to expand...

Highly suggest rolling your Pastor's head worn or lapel mic off from about 250hz to control that. Also check where the subs crossover point is at. No way in the world a spoken word mic should ever feed back through a sub. Your Pastor doesn't speak much below 250 ever, so why allow his mic to reproduce frequencies below 250?

Some guys have a tendency to make a spoken word mic very boomy in the low end in the same manner they Might be dialing in a kick drum. A spoken word voice should sound natural as if you were 5 feet away, not amplified like he was James Hetfield? Whoa-yeah!

I also make it a point to ensure that all of your vocals mics spoken and sung word have their LF roll off switch engaged on each channel. If you aren't or can't make sund down there in a natural manner, never give a mic the ability to reproduce tones down there.

Happy Eastering Up dudes!
 
#8
Keithwah said:
Highly suggest rolling your Pastor's head worn or lapel mic off from about 250hz to control that. Also check where the subs crossover point is at. No way in the world a spoken word mic should ever feed back through a sub. Your Pastor doesn't speak much below 250 ever, so why allow his mic to reproduce frequencies below 250?

Some guys have a tendency to make a spoken word mic very boomy in the low end in the same manner they Might be dialing in a kick drum. A spoken word voice should sound natural as if you were 5 feet away, not amplified like he was James Hetfield? Whoa-yeah!

I also make it a point to ensure that all of your vocals mics spoken and sung word have their LF roll off switch engaged on each channel. If you aren't or can't make sund down there in a natural manner, never give a mic the ability to reproduce tones down there.

Happy Eastering Up dudes!
Click to expand...

Oh yeah, I learned that lesson years ago. I high pass everything now. Including the kick and bass (can set the high pass all the way down to 20Hz, with a variable slope).
 
#9
KingRazor said:
Oh yeah, I learned that lesson years ago. I high pass everything now. Including the kick and bass (can set the high pass all the way down to 20Hz, with a variable slope).
Click to expand...

kick and electric bass don't produce much sound past 45-50hz, below 45 is just synth bass stuff and thats assuming you have a sub that can hit low down to 20hz, most amps have the option to roll off around 30-40hz because nothing important happens down there, other than ruining most subs.

As for your subs, you can run them off your mains (because they have a built in crossover that qsc programs) or you can send a line from your dbx rack to the sub and separate signals to your mains. its hard to tell the exact direction bass is coming from below 80Hz so that is a good place to start your crossover. Some systems may sound better if the cross over is higher at like 90 or 100hz or even 125hz (mackie cough....) but I find the sweet spot for most systems is between 80-100hz. I do not however recommend rolling off the mic below 250hz, your pastors voice will sound empty. People have short attention spans and a empty voice leads to zzZZzz's. I do roll off around 100-150hz depending on how deep their voice is. Definitely don't send an aux feed to the sub, that is what your drive rack is for, you use aux sends generally for monitors, sometimes for recording or mixes to your lobby area.

pick up 31 band GEQ's for your monitors to tune out feedback, but more often than not, placement and limiting stage volume is more effective and cheaper.

By the way, the feedback suppression thing on the dbx rack will cut out sustained notes from your vocalists and guitar... so... yeah, don't bother with it until the pastor does his thing.
 
#11
To be honest, the DRPX is really unnecessary. QSC has already taken care of the processing so using the DRPX is redundant and probably will cause more headache than it's worth. You are better off selling the thing and apply the funds toward enough graphic EQs to cover your monitors OR better yet, another sub.

If you go without the DRPX, you would go from your main out(s) to the sub and to the k12s. You would use the internal crossover from the ksub to separate the highs and the lows. For monitors go, from your aux outs to the GEQ then to the monitor. It is most effective if each monitor gets its own channel of GEQ. Otherwise you could "post eq" and use the onboard PEQ to filter out the feedback. This is probably not as effective though.

However, if you do choose to keep the DRPX, go from your main outs to the DR and from the L/R outs on the DRPX to the subs then from the subs to the k12s. You would still be using the internal crossover in the ksub. The DRPX would process your system as a whole. You would still need GEQ for the monitors though.

Lastly, because the QSC's don't really need processing, you could use the DRPX for the monitors. It's a little overkill but that's where you'll get the most use out of the DRPX with the gear you currently have. Go from your aux outs to the DRPX and from the DRPX main out to each of your monitors.
 
#12
jplumansoc said:
kick and electric bass don't produce much sound past 45-50hz, below 45 is just synth bass stuff and thats assuming you have a sub that can hit low down to 20hz, most amps have the option to roll off around 30-40hz because nothing important happens down there, other than ruining most subs.

As for your subs, you can run them off your mains (because they have a built in crossover that qsc programs) or you can send a line from your dbx rack to the sub and separate signals to your mains. its hard to tell the exact direction bass is coming from below 80Hz so that is a good place to start your crossover. Some systems may sound better if the cross over is higher at like 90 or 100hz or even 125hz (mackie cough....) but I find the sweet spot for most systems is between 80-100hz. I do not however recommend rolling off the mic below 250hz, your pastors voice will sound empty. People have short attention spans and a empty voice leads to zzZZzz's. I do roll off around 100-150hz depending on how deep their voice is. Definitely don't send an aux feed to the sub, that is what your drive rack is for, you use aux sends generally for monitors, sometimes for recording or mixes to your lobby area.

pick up 31 band GEQ's for your monitors to tune out feedback, but more often than not, placement and limiting stage volume is more effective and cheaper.

By the way, the feedback suppression thing on the dbx rack will cut out sustained notes from your vocalists and guitar... so... yeah, don't bother with it until the pastor does his thing.
Click to expand...

We don't have a dbx rack. Or any rack, for that matter. The mains and sub are powered. The sub and monitors are both fed by different AUXes.

I actually have the high pass on the Pastor's mic set at 266Hz. I also have a 6dB dip around 500Hz. His voice still fills the room. No lack of energy there. I just use the board's RTA to figure out how to EQ each channel. Pull out the offending frequencies, and (if necessary) add more of the frequencies I do want.

I don't ever have issues with monitor feedback, it's usually feedback from the mains from a mic being too hot (usually it's because there multiple mics that are too hot).

I roll of the kick drum at about 60Hz. The fundamentals of a kick drum don't go below that. The bass is high passed at about 40Hz with additional roll off from a low shelving filter because the church bass pumps out a ridiculous amount of low end, far more than is necessary (or useful).
 
#14
Tomis17 said:
To be honest, the DRPX is really unnecessary. QSC has already taken care of the processing so using the DRPX is redundant and probably will cause more headache than it's worth. You are better off selling the thing and apply the funds toward enough graphic EQs to cover your monitors OR better yet, another sub.

If you go without the DRPX, you would go from your main out(s) to the sub and to the k12s. You would use the internal crossover from the ksub to separate the highs and the lows. For monitors go, from your aux outs to the GEQ then to the monitor. It is most effective if each monitor gets its own channel of GEQ. Otherwise you could "post eq" and use the onboard PEQ to filter out the feedback. This is probably not as effective though.

However, if you do choose to keep the DRPX, go from your main outs to the DR and from the L/R outs on the DRPX to the subs then from the subs to the k12s. You would still be using the internal crossover in the ksub. The DRPX would process your system as a whole. You would still need GEQ for the monitors though.

Lastly, because the QSC's don't really need processing, you could use the DRPX for the monitors. It's a little overkill but that's where you'll get the most use out of the DRPX with the gear you currently have. Go from your aux outs to the DRPX and from the DRPX main out to each of your monitors.
Click to expand...

I'm not sure what DPRX is, I think you're referring to the dbx DriveRack PX? The QSCs have some DSP functions builtin:
crossover
time alignment
limiter to protect against over-excursion
heat management
DEEP(tm) bass enhancement
"intrinsic correction" to compensate for (I don't know what)
an EQ switch that can be set for "ext sub", "normal" or "DEEP"
a high mid bump switch for vocal enhancement

The most important functions of the dbx are not included in the speakers:
real-time spectrum analysis with a microphone to tune the system to the room including:
- auto-EQ
- auto-level balancing
- auto-feedback suppression including selectable-width fixed and dynamic notch filters.
- compression
whatever else, I'm not even done reading the manual.

The crossover and limiter are probably redundant, that's about it.

The auto features of the dbx are great for me because:
(a) I'm a beginner at sound reinforcement and don't have the skills to do a better job manually.
(b) Up on stage I don't hear the same thing as the audience, so my ears get fatigued differently from them as the night goes on and even if I did walk out there with my wireless I wouldn't perceive the same thing as them, so I couldn't do a better job manually.
(c) As a child of the Hard Rock 1970s I'm sure my ears are more battle-worn than the average audience ears thus they don't perceive the same thing in any case, so I couldn't do a better job manually.

I'd like to avoid adding GEQs because:
they cost money
they add weight & take up rack space
sprinting to the stage for an emergency feedback fix is not fun and does not impress club owners or audiences.

It remains to be seen whether the auto feedback suppresion on the dbx is really "all that and a bag of chips" but I'm going to give it a chance.

I like your idea of going from the dbx main out to the sub and then to the K12s. I'm more confident that the qsc builtin crossover is right for the qsc speakers than the dbx's preset for K-series. Since I only have one sub I guess I would go:

dbx left out -> Ksub w/internal crossover -> K12 -> K12
dbx right out -> monitor -> monitor -> monitor

The "run the subs off an aux" camp would suggest this instead:

dbx left out -> K12 -> K12
dbx right out -> monitor -> monitor -> monitor
mixer aux out -> Ksub, getting bass guitar and kick drum only

I will just have to try it both ways and see if there's a perceptible difference.

That way the dbx can ring feedback out of everything in one pass and I can get all the features mentioned above in a 1U rack space for less than the cost of a pair of good GEQs.

If I ever want to go stereo I can just give the monitors their own dbx.

I really hope this thing performs as advertised - that remains to be seen.
 
#20
dbx left out -> Ksub w/internal crossover -> K12 -> K12
dbx right out -> monitor -> monitor -> monitor

versus

dbx left out -> K12 -> K12
dbx right out -> monitor -> monitor -> monitor
mixer aux out -> Ksub, getting bass guitar and kick drum only

I'm thinking the second scenario might be better because the Kseries crossover is always going to be there. Fixed in the Ksub, switch-selectable in the K12s. If the dbx crossover is added to that it's possible that it might not play well with the Kseries crossover. For example if the dbx crossover is at 100Hz and the Kseries is at 80Hz, the mains would be starved for the frequencies between 80 and 100. Even if they're both at 100Hz, they will be some margin of error between them that might make a great crossover sound like a not-so-great one.

In scenario 2 the dbx will send full-range to the K12s and I can set their internal crossovers for external sub using their switches, then send bass guitar and kick drum only to the aux-fed Ksub which will use it's internal crossover. Adding vocals or keyboards to the aux sub mix would be as simple as turning a channel aux level knob.

I think that (in theory) gets at the best of all the equipment.
Only drawback I can think of is that the dbx won't be able to do auto-feedback-suppression on the Ksub, but it's a small frequency range. Shouldn't be hard to control that with the aux master or the channel tone controls on the board.
 

Latest posts

Top Bottom
Back