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Author Topic: Sub array behind live stage, how is this possible?  (Read 807 times)

Ash Priba

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Sub array behind live stage, how is this possible?
« on: August 30, 2017, 03:25:42 am »

Subwoofer arrays too close to a live stage can cause all sort of phase problems and feedback on the open mics.

Then how is this possible?

This is the Wall of bass installation in a european club (See attached image and youtube video explanation)
https://www.youtube.com/watch?v=pdM57_C-OEE

Case study on the installation
http://www.fast-and-wide.com/more/wideangle/5225-case-study-the-wall-of-bass

---

Is the solution as simple as a lowcut on the mic channel?
« Last Edit: August 30, 2017, 06:05:10 am by Ash Priba »
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Ivan Beaver

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Re: Sub array behind live stage, how is this possible?
« Reply #1 on: August 30, 2017, 11:44:58 am »

I would disagree with some of the comments in the video.

The idea of "no reflections" is kinda wrong.  Each driver is still behaving as an independent radiator, producing its own wavefront-that is radiating in all directions.

WHen you model something like this, you are looking at a steady state signal, and everything is nice.

But in reality, music is NOT steady state.  so the impulse response will show different arrival times if different drivers at different positions.

This can result in a "smearing" of the signal, due to the different arrival times.

Of course the amount of smearing depends on a number of factors.  The freq, the distance between arrival times, the difference of level between arrival times and so forth.

In the real world, it is not always so simple.

Some of the concepts are correct, but others are flawed.  What about the side walls and ceiling and floor? and the reflections off of them?  I did not see that addressed.  Sometimes you have look a bit deeper.
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Don T. Williams

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Re: Sub array behind live stage, how is this possible?
« Reply #2 on: August 30, 2017, 01:47:20 pm »

In many (if not most) concert situations, the subs are so omnidirectional that it probably doesn't matter if they are in front of or behind the stage.  Even when run in cardioid, there is significant bass on stage on either side of the stage center line.  I suspect this is especially true of smaller and club situations, so I would think it isn't much more of a problem that if the subs were in other locations.  And, yes a high pass filter on mics will always help! 
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lindsay Dean

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Re: Sub array behind live stage, how is this possible?
« Reply #3 on: August 30, 2017, 02:19:50 pm »

those "subs " look like mock ups
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Ash Priba

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Re: Sub array behind live stage, how is this possible?
« Reply #4 on: August 31, 2017, 06:00:27 am »

those "subs " look like mock ups

I believe each driver is enclosed in 400kg of concrete.

There is a longer discussion here
http://www.avsforum.com/forum/155-diy-speakers-subs/1510495-club-sub-s-oewall-bassa.html
« Last Edit: August 31, 2017, 06:12:37 am by Ash Priba »
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lindsay Dean

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Re: Sub array behind live stage, how is this possible?
« Reply #5 on: August 31, 2017, 03:58:11 pm »

hi pass on the kick .........wait,.....what?   Don?
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Don T. Williams

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Re: Sub array behind live stage, how is this possible?
« Reply #6 on: August 31, 2017, 04:25:23 pm »

hi pass on the kick .........wait,.....what?   Don?

Yes, if you have a console with sweepable high pass filters that are reasonably steep.  You probably will not want to do it with a fixed 80Hz or 100Hz high pass (low cut) filter UNLESS it's the only way to solve a problem.  Even then, with those frequency high pass filters in, your channel eq is still effective and you can get more bottom end.  You may find you can really tighten up the kick sound and get rid of problems by using the filter.  If it doesn't help, don't use it!

If you have steep sweepable filters, setting a filter at 20 to 40Hz (or what ever is needed) can tighten the sound, protect your subs from over-excursion, and solve some feedback issues.  It's worth trying, and it's very easy to turn on and off for comparison.
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lindsay Dean

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Re: Sub array behind live stage, how is this possible?
« Reply #7 on: August 31, 2017, 05:05:54 pm »

yes I got that,
 I was talking about the kick a few feet in front of this apparently real wall of subs.
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Don T. Williams

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Re: Sub array behind live stage, how is this possible?
« Reply #8 on: August 31, 2017, 05:33:28 pm »

yes I got that,
 I was talking about the kick a few feet in front of this apparently real wall of subs.

Well it may not be a wall of subs, but we have single or double 18" subs even closer to the kick mic(s) for the drummer's monitors.  Some drummers need (want) them really loud, and it's usually not a huge problem.  With the lows coming from a large source (the entire back wall), it may be at a lower level at the kick mic than these drum monitor subs are run . . . or it may be louder.  I haven't worked a venue like that one.
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Luke Geis

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Re: Sub array behind live stage, how is this possible?
« Reply #9 on: August 31, 2017, 06:16:17 pm »

I can see this working quite well actually.

Think about this. If you are directly in front of the wall of sound you can sort of get an idea of what you sound like. So the bassist that thinks its cool to rattle pictures off walls three miles away will know really quick how crappy that sound when the whole band is in there. I imagine it helps tighten thing up quite a bit on the low end. As to mic bleed, I don't think it would be any worse than most other situations.

I have run a main PA behind me before ( when I was playing in a band ) and it worked rather well. Yes you could not quite get the SPL before feedback, but you knew right away what was going on.
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