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Reducing off site bass

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URL: https://forum.speakerplans.com/forum_posts.asp?TID=106547
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Topic: Reducing off site bass
Posted By: citizensc
Subject: Reducing off site bass
Date Posted: 17 September 2021 at 7:09am
Hi Guys

Over the weekend just passed I coordinated the first edition of a small dance music festival ~1000 attendance

Over all, I think it went well, feedback was very positive and people are already asking about the next one!

One big issue we had was off site bass. The festival is about 4km from a town, for the most part people in the town reported they could hear nothing but we did get two noise complaints. This may sound insignificant but as a result we had to dramatically turn the volume down in the second night. 

We have already begun the planning stage for the next one in April and I am looking for effective strategies for reducing the off site bass. 

A little more info:
-The stage is pointed the opposite direction of the town
-The system is in a stretch tent with a closed back
-The system consists of 12 punishers and 4 xtros in two ground stacks
-There are no issues with mids/highs at all, the issue is bass (<120hz)
-The stage and sound system are contained by a 10x15m stretch tent

Some ideas of how to reduce bass behind the stage (in the direction of the town)
-build horn extensions, something similar to the x-horn from void - in theory a greater radiating area results in better directivity
-Hire some kind of noise barrier -  https://echobarrier.com/product/h8-acoustic-barrier" rel="nofollow - https://echobarrier.com/product/h8-acoustic-barrier - Cost? Effectiveness? Will the bass just go around it?


There are a lot of euro/UK members on here and I can imagine you guys content with these issues a lot, especially with outdoor events and high population density relative to Australia? 

What kind of measures have you guys uses? how effective was it?








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https://www.facebook.com/voyager.system

@voyager_soundsystem



Replies:
Posted By: APW
Date Posted: 17 September 2021 at 9:43am
Cardioid/end fire sub array.



https://forum.speakerplans.com/how-to-cardioid-sub-arrays_topic26007.html" rel="nofollow - https://forum.speakerplans.com/how-to-cardioid-sub-arrays_topic26007.html


Posted By: AndyWave
Date Posted: 17 September 2021 at 10:47pm
Hire acoustic tech with noise monitoring stations to the direction of complaints. That would solve also false noise complaints from people who don't appreciate your kind of music...
And the dedicated noise measuring tech will have eye on the measurement stuff during event and avoid tampering.

A competent tech would also help You to tune and position your bass rig with maximum cancellation to the relevant direction.

I assume You have some kind of legislation of decibel levels which are considered as nuisance. -3dB from that and You win with evidence, if You let me say.

And Yes, cardioid array, or one step further, end fired array iow 3 or 4 subs in a row with appropriate delays. At some point this costs too much in amp channels and processing, unfortunately.

My tuppence worth, Andy





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torturing electrons since ......


Posted By: APC321
Date Posted: 18 September 2021 at 9:03pm
You say "the stage is pointed the opposite direction of the town".

So the sound system is projecting into the audience, pointing away from the town.

But a lot of bass energy will be going in the opposite direction.

Recently I came across a sound system set up outdoors in a large park for a fitness class.Probably about 50 people. They were using a pair of stacks separated by about 4m, comprising single sub per side, with a JBL EON top box on a pole mount. They were playing "house" music at a decent volume. So I thought that I would have a listen.

I walked about 100m back from where they were, and then I walked in a big circle all around them, keeping the same distance from them.

In front of the stacks you got power alley as you expect. Tailed off at the sides. But as I walked around the back, there was almost as much bass as in front of the stacks, with a power alley in the same way as the front.

I wonder you re-orientated the stage by 90 degrees you could take advantage of the tailing off at the sides?





Posted By: toastyghost
Date Posted: 18 September 2021 at 9:39pm
A horn loaded bass system at a reasonable mouth area & ground stacked is not comparable to a couple of reflex subs in terms of polar response.

The Punisher is a relatively small cabinet, but a stack of 6 per side would create a mouth area large enough to give a pretty directional response > 70 Hz.

However the left/right power alley will be creating a laser beam of sound pressure both front and backwards.

The best approach is to get off site and on site measurements done during the show by trained professionals who understand the type of event, have a hotline for complaints during the show to respond - probably the most effective tool based on a fair bit of research, even if the changes made in response to a call on site are minimal - and a bass array design that specifically targets off site noise reduction.

Here’s where FLH subs are in an ‘unknown state’ as there’s a compromise between the required mouth area for the boxes to work properly, and the practicalities of array design such as spacing, offsets and the like.

Reducing the mouth size will create significant ripple in the reactance of acoustic impedance, which translates to reduced linear output and possibly increased thermal rise and distortion. With the punisher being quite small and already at risk of overheating, you may need to consider a minimum of four boxes as one ‘sub’ for array purposes.

A ‘graveyard’ of subs out front of stage is never going to fly, so going super deep in end fire isn’t really practical. You also have the issue of a relatively narrow notch in response at the rear.

I’d suggest a two deep classic Olson gradient system in front of stage, and putting your mains on risers left & right instead if you can’t fly them. The maths is relatively simple, and you’ll get the most broadband cancellation. Yes, the timing out front is compromised further by an additional rotation in phase. However, you can consider whether that’s audible against the many other factors in play.

It’s easy to add a second order all pass filter @ 63 Hz to a track of your choice in Reaper on your computer and listen with headphones versus an unprocessed track in an A-B test. If you can’t hear it then, you certainly won’t hear it out front on a PA. Yes, lots of engineers state they use end-fire for improved transient response, but I’d wager that in most cases the combined bass array’s response simply hasn’t been accounted for when aligning and tuning the system as a whole in the field.


Posted By: Contour
Date Posted: 18 September 2021 at 9:45pm
Any pictures of the event available? 


Posted By: toastyghost
Date Posted: 18 September 2021 at 9:56pm
Originally posted by Contour Contour wrote:

Any pictures of the event available? 


A latitude & longitude for Google Earth might be more useful mark up any noise sensitive properties.


Posted By: ceharden
Date Posted: 19 September 2021 at 10:14pm
You may find that the tent is in fact part of the problem.  I've often noticed when doing gigs inside any kind of tent or marquee that you appear to get more bass outside it than inside (that may be mostly perceived).

If you imagine you've put a large source of bass inside a tent, it doesn't really matter which direction you point it because it's effectively going to cause all of the walls of the tent to move, re-radiating the bass, probably in all directions.  Any kind of speaker directivity really only works in free space IMO.



Posted By: Requiem
Date Posted: 20 September 2021 at 8:02pm
Hi so I have a query linked to this same issue, around reducing noise pollution to the surrounding area for a 2 day festival. 

The festival is a celebration of our sound systems 10th and 11th birthday so naturally we want it to be as impressive as possible, so the plan was to bring in a few extra subs so that I can set up 24x MA WSX & 8x EAW KF750, which of course are very loud cabs, I am trying to ease the disturbance to the local neighbours which are 400m, 650 and 750m away respectively, in opposite directions, across fields and low shrubs / hedges with some, but not much, tree coverage.

I was planning a quadrophonic setup inside a barn with 4x stacks on PA risers (which is the reason I was going for 24, for 4x nice matching stacks of 6 +2), with noise propagation in the form of heavy acoustic draping around the inside of the barn, the walls of which are wooden slats. I was also planning to hang big heavy wool bales, which are fairly dense and absorbent, directly behind each of the stacks inside the barn , and then a 12m wide by 4.5m high wall of hay bales along one side of the barn which faces onto the closest, 400m away neighbour, who apparently is a right pain.

I was hoping the quadrophonic setup would provide cancellation outside of the arena, whilst inside meaning that the audience members are never far from a stack, hopefully meaning we wont need to drive it as hard as we don't need to project it as far? and that the acoustic draping would contain the high frequencies whilst the wool bales and hay bale wall would reduce bass pollution. The farm owner is also keen to keep the sound within a respectable level.

Our license conditions are harsh but not unusual, and we are expected to keep to 65db from the nearest residences Unhappy. We will have our own person travelling between the residencies taking 15m average readings and staying in touch with us reporting back.

I realise my plan probably seems ambitious, I would like to hear others view on it and if they have anything to add that could help? I've not tried a quadrophonic array before, I decided on it as we are having to reduce sound in three separate directions in a rough triangle, and due to the placement of the barn in relation to those directions.

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www.requiem-soundsystem.com


Custom Martin Audio WSX, USB & CSG Soundsystem based in Bristol


Posted By: KDW32
Date Posted: 20 September 2021 at 10:22pm
Bails of hay stacked up behind each stack should help.


Posted By: toastyghost
Date Posted: 20 September 2021 at 10:57pm
I’ve been modelling ‘four point’ stacks - quadrophonic was a specific type of audio format - a few times in the last year using all sorts of cool toys. Unfortunately in almost all cases, it showed that the attempts at ‘controlled chaos’ are pretty much bogus, for the low end.

Get on Google Earth, make a project file and pin all the houses nearby that you can find. Those are your noise sensitive properties.

Once you know where they are, you can use stage orientation, bale placement, and subwoofer array design to help get the results you want.

It has a ruler tool so you can even do some basic inverse square law calculations. Assume the sub array is an omni or dipole source, set the broadband sub level you’d like in the low end on the dance floor (I find that 114 dBC slow with 130 dBC peaks is good) as the start point, and then just do some logarithmic maths to calculate the level at the given distance for the nearest house.

Off your rough distances, a 65 dBZ level at the 400 m would be 117 dBZ on the dance floor. But don’t get too excited - an instantaneous peak isn’t a good description of nuisance noise. You need to consider the Leq - a time based average - with suitable weighting to compare on site levels to off site.

The WSX is a FLH just like the Punisher, so my rule of thumb above applies. Treat a block of four subs as a single box, and design a gradient or end fire sub array to suit.

If you need cancellation in a direction, put a two deep set of block of four subs facing the opposite way, spaced at a distance of 1/4 wavelength of your chosen centre frequency (63 Hz is a good start), then delay the rear stack the same distance and polarity invert it. Hey presto, broadband cancellation.

You can put them central to the stage, off to one side, in three places all firing in - whatever. The cardioid array is what will do the work.

If you wanna go ‘quad’ for the mains to give that vibe, then you can do that with them on risers. Just be aware that time alignment in those circumstances is a case of choosing points to average the error or ‘wrongness’ across…


The AES paper on event noise management is open access, by the way:
https://www.aes.org/technical/documents/AESTD1007_1_20_05.pdf" rel="nofollow - https://www.aes.org/technical/documents/AESTD1007_1_20_05.pdf


Posted By: imageoven
Date Posted: 21 September 2021 at 8:41am
Originally posted by Requiem Requiem wrote:

the closest, 400m away neighbour, who apparently is a right pain.


400m to someone keen to complain? sounds like a non starter to me.


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Keep pushing on, things are gonna get better.


Posted By: woody2
Date Posted: 21 September 2021 at 9:45am
Originally posted by citizensc citizensc wrote:



we did get two noise complaints.

What kind of measures have you guys uses?







rohypnol.


Posted By: snowflake
Date Posted: 21 September 2021 at 10:07am
Originally posted by toastyghost toastyghost wrote:



The AES paper on event noise management is open access, by the way:
https://www.aes.org/technical/documents/AESTD1007_1_20_05.pdf" rel="nofollow - https://www.aes.org/technical/documents/AESTD1007_1_20_05.pdf

interesting discussion of meteorological effects at p.69

if one of your problem neighbours happens to be a at a distance where atmospheric refraction is directing sound it would be useful to be able to create a cancellation in the vertical pattern from your stack and point the null at the problematic angle. I you create a vertical stack (perhaps about 3m) with some of the boxes at the bottom rear-firing and phase inverted, could you not then steer the vertical pattern with delay? Might be hard to predict - but if you found you suddenly had a problem half a mile away due to changing weather conditions you could try varying the delay and see if the problem goes away again. Wish I had the equipment and space to test this out but it's just an idea...


Posted By: toastyghost
Date Posted: 21 September 2021 at 10:52am
Originally posted by snowflake snowflake wrote:

Originally posted by toastyghost toastyghost wrote:



The AES paper on event noise management is open access, by the way:
https://www.aes.org/technical/documents/AESTD1007_1_20_05.pdf" rel="nofollow - https://www.aes.org/technical/documents/AESTD1007_1_20_05.pdf


interesting discussion of meteorological effects at p.69

if one of your problem neighbours happens to be a at a distance where atmospheric refraction is directing sound it would be useful to be able to create a cancellation in the vertical pattern from your stack and point the null at the problematic angle. I you create a vertical stack (perhaps about 3m) with some of the boxes at the bottom rear-firing and phase inverted, could you not then steer the vertical pattern with delay? Might be hard to predict - but if you found you suddenly had a problem half a mile away due to changing weather conditions you could try varying the delay and see if the problem goes away again. Wish I had the equipment and space to test this out but it's just an idea...


In principle yes, but it’s not typically the bass that causes that refraction issue. Additionally you need to consider the mirror image sources in the infinite baffle space of the ground, which is more complex than you think:
https://www.merlijnvanveen.nl/en/study-hall/135-which-sub-to-reverse" rel="nofollow - https://www.merlijnvanveen.nl/en/study-hall/135-which-sub-to-reverse
https://www.merlijnvanveen.nl/en/nl/studiezaal/137-which-sub-to-reverse-pt-2%20" rel="nofollow - https://www.merlijnvanveen.nl/en/nl/studiezaal/137-which-sub-to-reverse-pt-2

However this is yet another area where actual research and testing ‘out in a field’ is needed. I really wanted to try and work on some of the things in this report for my dissertation, but the uncertainty of COVID regulations over summer time meant I had to choose something safer to focus on back at the start of the year 🥲

More of an issue is the low mid and vocal region. A major problem with big banana hangs of line array is the massive rear lobe that comes off the system straight into the sky; it’s a huge reason behind the focus on passive or active cardioid designs in modern line array systems like d&b’s GSL/KSL, Fulcrum’s FL283, and the use of flown subs behind the main hangs.

That doesn’t help address things out front though. Meteorological factors are logged with mappings by the good types of noise management teams, but I’m not sure how much of that is fed back into research - let alone how much of the data is viable given the lack of controls.

There’s more info on the very complex Nord2000 noise model here:
https://eng.mst.dk/air-noise-waste/noise/traffic-noise/nord2000-nordic-noise-prediction-method/" rel="nofollow - https://eng.mst.dk/air-noise-waste/noise/traffic-noise/nord2000-nordic-noise-prediction-method/
https://forcetechnology.com/en/innovation/completed-projects/nord2000-noise-calculation-method-auralisation" rel="nofollow - https://forcetechnology.com/en/innovation/completed-projects/nord2000-noise-calculation-method-auralisation


Posted By: martinsson
Date Posted: 10 October 2021 at 11:13am
Abit crazy perhaps, but has anyone on here tested any active solution? For example a bunch of standard 218 boxes, each fitted with a primitive x-over, a mic and a power amp.

The idea has been tested for improvement of room acoustics, a box producing a level matched inverse of the ambient lf, could something similar be used for off site lf suppression in a half space environment?

Just a thought.


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Swedish Pro-fi diy-nerd - http://www.martinsson.cc/blog/" rel="nofollow - http://www.martinsson.cc/blog/


Posted By: toastyghost
Date Posted: 10 October 2021 at 11:37am
Originally posted by martinsson martinsson wrote:

Abit crazy perhaps, but has anyone on here tested any active solution? For example a bunch of standard 218 boxes, each fitted with a primitive x-over, a mic and a power amp.

The idea has been tested for improvement of room acoustics, a box producing a level matched inverse of the ambient lf, could something similar be used for off site lf suppression in a half space environment?

Just a thought.


Yes. Some examples are in the AES document, and Rocket Science in Switzerland are the front runners in a system that reacts fast enough. A friend of mine is doing a thesis on it from January.

It’s a lot harder than you think, and has its own issues in the world of perception and psycho acoustics.



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