Reducing off site bass

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.

snowflake wrote: 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 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
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/
https://forcetechnology.com/en/innovation/completed-projects/nord2000-noise-calculation-method-auralisation

Edited by toastyghost - 21 September 2021 at 11:09am

citizensc wrote: we did get two noise complaints. What kind of measures have you guys uses?

rohypnol.

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

Edited by toastyghost - 20 September 2021 at 11:09pm

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 . 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.

Contour wrote: Any pictures of the event available?

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