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Author Topic: Lowering low frequency noise n stage  (Read 933 times)

Kenny Phillips

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Lowering low frequency noise n stage
« on: June 18, 2018, 06:30:46 pm »

Hello All,
I have a small outdoor stage.  I notice quite a bit of low end on stage from the subs which makes sense due to the omnidirectional nature of the lower frequencies.  Even when I do not use the subs, I still notice excess low end.   Along with that I also measured a bit of an increase in 65hz and 130hz on stage.  So I was wondering if anyone has experimented with the idea of actually putting a sub on stage, and feeding it with just enough out of phase sub to cancel some of the low frequency noise.  By setting the eq up to be emphasize the 65hz and/or 130hz I may get more of an effect.

My thinking is along the lines of noise cancelling headphones and other applications of inverted feedback.

Any thoughts?
Kenny
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Luke Geis

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Re: Lowering low frequency noise n stage
« Reply #1 on: June 18, 2018, 07:37:02 pm »

You will need to change your user name to your real name to get much further here on this forum ( as per the rules ).

I will answer anyway though. Yes that has been done and no it does not work very well. Three real problems with that idea.

1. The sources of noise comes from different locations, so the sub on stage could only ever cancel frequencies at the ONE location that you set it to have maximum rejection. As soon as you move, game over.

2. Now you have sub energy from the stage that will interact with your FOH sound. It won't get better, only worse.

3. You have just added another source of noise that costs money to have an implement and that device just adds more noise to the stage.

One way to reduce rumble on stage is to isolate them more with perhaps a sand barrier, concrete structure or some other way to make the stage not resonate. You could implement a cardiod sub setup, but that requires the subs to be next to each other. However FOH sub content is usually not as bothersome as most think as long as it is not blasting into the mics like crazy. Let me explain.....

The sub energy should really only contain kick and bass for the most part, so while it is obviously going to be heard, if it sounds good and right, it shouldn't be too bothersome. If it makes the whole stage rattle, it is a sonic tuning issue. Reduce the offending frequencies to reduce the soaring rumble. Next thing that most never consider is MONITORS..........Monitors add a crap ton of low end energy that is really of no need. If you are not hi-passing your monitors up to 140-200hz, there is most certainly low end gunk flying out of them all over the stage. Next is the stage floor. Basically a huge diaphragm that is really good at making low notes and mid bass content reproduction. Sureing up the stage and making it sound as dead as possible will do more than you can imagine. If it resonates and makes sound, it will find its way into mics and your FOH mix.

The hardest part to help reduce rumble and over the top low end notes, is to get the band to change their tone. If the bassist is playing a note that makes the whole stage rattle, then he needs to turn down the bass, notch out that frequency ( if he has a graphic or parametric EQ ) and or turn down. If the guitarist has a note that makes things sing, again same thing, turn down the offending EQ band. Good musicians should be willing to help clean up stage noise issues.

Aside from that, it will come down to PA system tuning. Too much of a good thing is still too much. Getting the sound to be clean and a little more natural can really help clean things up. If the sound out front is bigger than life in every way, it will find its way back into a mic which further reinforces that sound out of the PA. Most of the offence I find though, exists from the monitors. The monitors will make a wooden, resonant stage really woof up and make for a sound guys worst nightmare.
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Kenny Phillips

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Re: Lowering low frequency noise on stage
« Reply #2 on: June 18, 2018, 10:15:33 pm »

Luke,

Thanks for your gracious answer in spite of my name faux pas.  Not sure how to change the name other than create a new profile with my real name.  Will fix it.

Looks like beefing up the stage as well as damping with sand is first order of business.  Planning on buying a cardioid sub and also placing the mains a little further of to the side of the stage.  Its just an open sided shelter 12x12 stage in the back yard, but my goal is to do it as well as possible.

Once again thanks

Kenny Phillips
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Luke Geis

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Re: Lowering low frequency noise n stage
« Reply #3 on: June 19, 2018, 02:18:06 pm »

My caveat to the cardioid subs placed on each side of the stage is this: Cardiod subs reject predominately in the rearward plane, which means if they are side stage, they will be ineffective at keeping energy off the stage. If you had a center cluster of subs, this would be a more viable solution.

I feel that making the stage non resonant will be the biggest help, followed by getting the monitors low end under control, then tuning the FOH system to not excite things on the stage. Cardioid subs are not as much help as their solution appears to offer. It requires a very specific situation for them to be effective; at least objectively.
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Tim McCulloch

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Re: Lowering low frequency noise n stage
« Reply #4 on: June 19, 2018, 09:48:36 pm »

My caveat to the cardioid subs placed on each side of the stage is this: Cardiod subs reject predominately in the rearward plane, which means if they are side stage, they will be ineffective at keeping energy off the stage. If you had a center cluster of subs, this would be a more viable solution.

I feel that making the stage non resonant will be the biggest help, followed by getting the monitors low end under control, then tuning the FOH system to not excite things on the stage. Cardioid subs are not as much help as their solution appears to offer. It requires a very specific situation for them to be effective; at least objectively.

A center cluster of subs will put about half it's energy right on the stage.
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Luke Geis

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Re: Lowering low frequency noise n stage
« Reply #5 on: June 20, 2018, 12:46:26 am »

With subs, I would argue that if they are in any vicinity to the stage, they will dump energy onto it. Hence why I stated that a cardiod array would be better suited if a center cluster was being used. That is not the case though. I was advising against using a center cluster in other words.

A cardioid array can be as little as two speakers side by side and can reduce rearward energy by 10db or more. Now if this was a center cluster, it would yield the lowest energy potential on the stage vs. any other option. I don't think the sub energy on the stage is the biggest issue though. I think it is resonance combined with system tuning. No way around having sub energy on the stage, so basically finding a way to reduce its effect is more viable.
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Ivan Beaver

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Re: Lowering low frequency noise n stage
« Reply #6 on: June 20, 2018, 07:56:11 am »


A cardioid array can be as little as two speakers side by side and can reduce rearward energy by 10db or more. .
You cannot do a cardioid array and have the cabinets side by side and get rearward cancellation.  At best, if one was facing backwards, the cancellation would be towards one side, but not both.  But this would also affect the forward radiation pattern, often in the wrong direction.

Ideally they need to be 1 behind the other, or 1 on top of the other, with the top one facing the rear-assuming the cabinets are deep enough to provide the distance needed for cancellation at the sub freq.
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Luke Geis

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Re: Lowering low frequency noise n stage
« Reply #7 on: June 20, 2018, 03:43:16 pm »

Actually, you can place them side by side and it will work, BUT you would have to rotate the cluster in unison to get the desired result. I.E. the cluster would be at an odd angle to the face of the stage. I did not clarify that, but was also not suggesting that he utilize such an array anyway. By my calculations you would have to rotate them about 45* and delay the front facing sub by roughly 2ms.

The 45* offset in angle places the acoustic centers in the same forward plane perpendicular to the stage. I did this once at a show that had large metal containers at a 90* with the stage backed into the corner that the containers made. The face of the stage was staggered ( Intellistage set up ) and I was able to place the subs and array them so that the cardiod pattern didn't build up in the corner as much. I used only two subs.
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Kenny Phillips

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Re: Lowering low frequency noise n stage
« Reply #8 on: June 20, 2018, 06:51:03 pm »

Hi Guys,
Attached is the stage I am talking about.  My goal is to provide the best sound for both the audience and the musicians and to be a good neighbor.  Hence the leaning towards cardioid subs.

I know that from a practical matter a couple speakers on sticks is more than adequate to entertain. But I learn a lot more if I go with aux fed subs and matrix mixes and learning about phase and timing issues at the crossover points and the hundred other issues that can help fine tune a system.  It helps me a lot when I play guest sound guy for some of the local venues here in Black Mountain.

My other concern is monitor speakers.  At this point I am using 2 way 12" QSC's as monitors.  Considering going to a Hotspot type setup.  I remember using them in the early 80's, but was wondering if there is a really good sounding small monitor speaker these days.  Where would be the appropriate place to get some good input regarding monitor choices.

Thanks to all the people that make this forum a great place to learn.

Kenny Phillips
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Luke Geis

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Re: Lowering low frequency noise n stage
« Reply #9 on: June 20, 2018, 07:25:05 pm »

VERY NICE!!!!!!

The awning will also help keep bass rolling around in the space. It looks too nice to do acoustic treatment to that really. Also the low end coming off the mains will build up ( reflect ) onto the stage as well. If those are the only two monitors you are using, if you can keep the woof out of them, they won't be part of the problem as much.

Seeing this leads me to believe you will just have to do a conventional stereo sub deployment and tune the low end to not be problematic. Interestingly, if you do a cardiod sub arrangement with two subs on each side and do not splay them, you can get the energy from them off the stage and it will still act like a normal stereo sub deployment to everyone else.

Pics worth a thousand words. As you can see, side by side it creates roughly a 45* shift. If you invert this on the other side you will get whats in the second pic. As you can see, you will still end up with the power alley and the lobing, but it reduces energy on the stage area. This is with the subs placed about 20' apart and generated at 50hz with the forward facing sub delayed 2ms. 

The third picture shows what it would look like if you stacked the subs one atop the other. It does a better job at keeping more energy off the stage area, but they have to be further forward of the stage to do so. The delay time was also reduced to 1.5ms and the generation was made at 50hz. same spacing.

Depending on where in relation to the stage the subs will be would decide which is a better option. The side by side retains energy on the stage, but you can have them set further back almost even with the stage face and still have reduced sub content on the stage. With the typical one atop the other configuration, you can see that if the subs are even with the face of the stage the singer and those near the front of the stage will be slathered with low end, while the back of the stage has little or no sub energy. You would have to move the subs further forward of the stage face to keep energy off the front row of performers.

« Last Edit: June 20, 2018, 07:44:26 pm by Luke Geis »
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