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I have:
- Presonus Studio Live 16.4.2.
- 2 Main Speakers
- 2 Sub-woofers
- DBX DriveRack

Currently, my connections are as follows - L & R from the Studio Live goes to L&R inputs of the DBX DriveRack. L&R of the subs out from DBX go to the L&R Subs INPUTS while the L&R Mains OUTPUT go to the main speakers' INPUTS.
I have had problems with mics, especially the Pastor Mics, booming mainly from the Sub-Woofers. I have heard about AUXILIARY FED subwoofers. How should I do my connections to ensure that all the mic signals bypass the sub-woofers and go straight to the tops? Would appreciate a rough sketch diagram on how I should do the connections. Thanks!
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by wahlerstudios on Tue Jan 03, 2017 1:59 pm
Except of generally turning the volume of your subs down a little and checking, if their positioning is reducing or supporting feedbacks, I wouldn't touch the x-over stuff at all at the moment. If the PA otherwise sounds ok, look at all the input side of things. This aux sub thing will not really help you at this stage.

Let me say so: There should be no voice in the subs at all! What you can do as some kind of "first aid" is to use the very first encoder knob of your fat channel, which handles the "high pass filter" (frequencies above the setting can "pass"). Unfortunately on a legacy board this filter is not very effective, so you might need to use the bass filter of your fat channel additionally for this task. Simply try to get rid of low frequencies! A male voice does not need frequencies below 120 Hz (unless it's a bass singer...), mostly even 150 Hz is "deep" enough. Sometimes results are also good with the HPF set at 200 Hz. It always depends on the individual voice.

Avoiding "sub frequencies" on the input side should minimize your problem already. A change of the microphone is also always worth trying...!

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by sjc193 on Tue Jan 03, 2017 2:22 pm
Yes, use the High Pass Filter on the channel to cut the lows from that microphone (and any other mic that doesn't need lows.) I often will set the high pass up to 200 hz or even higher sometimes, do what sounds the best. For a big guy with a baritone voice (where I may actually want a little in the subs) I will set the high pass lower (100-150) but I will use the channel PEQ low band shelf cut to get the right amount so it's not too much.

I always thought of AUX fed subs as just something people do when they don't have a good crossover like your DBX Driverack. I just don't see any reason why you would want to do that when you have the DBX. People swear by it, but I just don't get it, learn to use the high pass filter per channel. . .

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by kencomchurch on Tue Jan 03, 2017 3:36 pm
Thanks greatly for the advice. My biggest problem is with the Pastor's ear-set mic. Right now the HPF on its channel is at 750 hz. If I go below that there's rumbling. Wondering if I have cranked up the subs way too high!
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by matthewseymour on Thu Jan 05, 2017 3:16 am
To give an alternative opinion.... I almost always go for a separate feed to subwoofers to avoid precisely this problem. Yes you can HPF a mic to avoid too much bottom end, but what you'll find is most high pass filters have a fairly gentle slope of maybe 12db octave. That means to completely avoid any thump from the subs from mic pops you often have to wind the HPF so high that things start to sound a bit thin.

So the question is does your driverack have another input? If yours has three inputs then you can take a post fade aux to the third crossover input and use that for the subs.

If you don't, another question is whether you need stereo. Often times, whilst it's sometimes nice, it's completely unnecessary in a church context. In which case you could actually just use your left/right and pans. Make left the tops and right the subs. The last church system I was responsible for worked this way and was very effective.
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by kencomchurch on Thu Jan 05, 2017 3:53 pm
matthewseymour wrote Often times, whilst it's sometimes nice, it's completely unnecessary in a church context. In which case you could actually just use your left/right and pans. Make left the tops and right the subs. The last church system I was responsible for worked this way and was very effective.

I am a bit confused here with the panning bit. My DriveRack PA2 has just two inputs. Please expound and thanks in advance for your contribution.
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by matthewseymour on Fri Jan 06, 2017 3:21 am
So I ran the whole system in mono. The left output of the desk fed all the mid-top speakers and the right output fed the subs. You therefore have control of whether any channel goes to the sub at all, and how much, using the pan controls. In practice I found we either sent stuff to the sub or not so things were either panned hard left or centre.

In this case we were using d&b e-pac amplifiers which contain a DSP so there was no crossover box in play, but the principle is the same.

This assumes you can run your driverack as a dual mono input and feed the subs from the right input and everything else from the left. I'm not familiar with all the driverack models so it may be you can't do that anyway.

When I'm doing aux fed subs with my own system I use a behringer DCX2496. This has three analogue inputs so I can run stereo if I wish for the mid-tops and a third feed for the sub and the dcx2496 lets you select which input is feeding outputs and what processing is in between.

I
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by matthewseymour on Fri Jan 06, 2017 3:25 am
A quick thought on mono vs stereo. I like stereo and will tend to set things up that way by default but I do think it's largely pointless for a lot of situations. Mainly because few people are in a position to take advantage of any stereo spread from the PA. The temptation to start panning things around can lead to a worse mix for much of the audience. In a church context there's even less benefit.

The system I talked about was an installed setup in a late medieval church building in the UK. There's seating facing forward and in from the sides, and a balcony. Left and Right has no meaning for most people in that context.
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by matthewgorman on Fri Jan 06, 2017 10:09 am
but what you'll find is most high pass filters have a fairly gentle slope of maybe 12db octave


IIRC, the slope on the legacy mixers is 6db, and it may be the same for the AI mixers.

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by wahlerstudios on Fri Jan 06, 2017 1:09 pm
The SL AI series brought -12 dB/8va to the High Pass Filter, which makes the filter very effective. It's mostly the only "processing" I use.

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by matthewseymour on Sat Jan 07, 2017 4:46 am
It all depends on the context. A bit of talking in between songs at a gig can handle some thump on the subs. Speech at a public meeting or a Congregational church context is a different matter. If you have a 12db octave high pass filter and general levels are sitting at around -30 on the meter, the plosives from speech could peak at -10 or higher. With that filter you're still going to be getting a good level of low frequency hitting the subs unless the hpf frequency is wound up quite high. That might be fine, depends a lot on the speaker and the overall system. When I do cathedral sound I have hpf wound up to about 300hz. No subs there of course.

In my own experience, if pops and bangs from speech hitting the subs is a problem, the two solutions are to stop those plosives hitting the mic through a better mic, mic position or pop filter on the mic, or to ensure that audio source doesn't get routed to the subs.
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by Dale Christenson on Sat Jan 14, 2017 11:19 pm
wahlerstudios wroteLet me say so: There should be no voice in the subs at all!

This is precisely the reason for aux fed subs...
When I had a completely passive system I had a DriveRack PA for the system. I found that having the vocal mics in the subs was undesirable. For a while I used the HPF. The vocal mics were still in the subs. Whether less or not, they were still in there. I wanted to employ aux fed subs to get the mics out of the subs. There is no content in a voice that needs sub support. So, I purchased a second drive rack to process the subs. I could then send and aux output to the sub DR and from there send out to the sub amp. Took the vocal mics out completely. Much better.
Now at this point, I have Presonus ULT15 top speakers, so I have a spare DR. The tops come directly from the RM32ai left and right outputs to the speakers themselves.
This is tricky only because you now have separate control of the subs volume level. And this is why people don't like it. Because if you don't set your system up properly, you get a mess. I love it and won't switch back.
An interesting thing about the RM mixers; Aux sends 13-16 have delay control. This could be helpful when aligning your subs to your top speakers. In my case, I have the subs out in front of the stage clustered about 4' in front of the top speakers.

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by roblof on Sun Jan 15, 2017 4:35 am
sjc193 wroteI always thought of AUX fed subs as just something people do when they don't have a good crossover like your DBX Driverack. I just don't see any reason why you would want to do that when you have the DBX. People swear by it, but I just don't get it, learn to use the high pass filter per channel. . .

The crossover is usually around 12-24dB/oct and many times set around 80-120Hz, approx the same as a hpf, so it won't have much impact in that neighborhood since a signal isn't reduced by 12-24dB at the crossover point.

The number of open mics is also a big factor to consider. Eight open mics with the same gain would have a combined gain of up to 9dB for a common audio source. This means that in the end you only get some minor hpf reduction for all of that stage rumble. You'll soon find that a normal hpf won't filter out all of the stage rumble sent to your haystacked subs, no matter how hard you try.

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by Ericwjohnson on Sun Jan 15, 2017 8:31 am
The last couple of years I've been using my Aux Sends to feed my subwoofers. (Just like a monitor mix) This way I have complete control of which signals are sent to the subwoofer and I get to use my EQ's to control the tone.
Typically only Bass guitar or Upright Bass, some percussion, etc. get sent to the subs. I also can control each instruments level and overall level of the subs. Some songs or tunes want a lot of bass and other numbers not so much. I can ride the aux send level to suit what ever comes up.
The only slight drawback is having an extra slider to change when the levels of the mains need to go up or down.
The new third generation 32IA mixer looks like it has asignable "Sub mix sliders" and I can't wait until the option becomes available on more of the Presouns mixers.
-Eric

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