using noise cancellation...

[Jody]

Hi.
when doing sound systems at summer festivals, i've often noticed the 'power alley' up the middle, and similar cancellation 'alley's'. How can these be predicted / mapped? and can the distance between stacks be optimised to maximise cancellation of the 50/60hz 'thump' in the sideways direction? I'm thinking that if the speakers were 0.5 1.5 or 2.5 x the wavelength of 50/60hz apart, then the omni-directional bass wave from each stack would be out of phase with the other stack, as it passed it. this sideways cancellation alley could be aimed at the nearest village, to minimise noise complaints from neighbors (too loud) and the dance floor (too quiet!).
I've just lost a very good job to a competitor, as i wasn't prepared to do a '6 stack noise cancellation system' despite :
1/having the best sound at last years festy
2/our stage not causing any of the noise complaints
3/being the preferred sound system of the promotors of the stage

I've looked after multi stack systems before, & i promised myself i'd never do it again!

I'm sure the council loved to hear about all the super duper cancellation technology blah, but my responsibility is to the dance floor, and i'm trying to reproduce stereo, not a train crash.

pleeez help meeeeeee!

[JBL 4645]

With the other stack (out off phase) well the only think that’s crossing my mind is the phantom centre signal where the two signals meet each other and double in sound pressure.

[boputnam]

...when doing sound systems at summer festivals, i've often noticed the 'power alley' up the middle, and similar cancellation 'alley's'.

That there is definition "comb filtering" effect - the result of two signals of the same frequency having different distances to the listener. This creates nodes (summation) and nulls (cancellations). There is bunches written on this - not a trivial topic.

It most often occurs due to interactions between closely-spaced (multiple) loudspeakers (cf Handbook for Sound Engineers, Glen Ballou, ed, p1251-1252).

How can these be predicted / mapped?

SmaartLIVE and other laptop-based applications can do this - it takes time and knowledge - you need to walk the field and map the response using (commonly) Pink Noise. Then, you must adjust the stacks, re-measure, repeat. Repeat again. You will learn what works and what doesn't - often, fewer will be better...

and can the distance between stacks be optimised to maximise cancellation of the 50/60hz 'thump' in the sideways direction?

Yes. You can try putting the subs in the center stage - this avoids the summation.

Also, if you can adjust the gain of each sub "stack", lower the gain of one side and you will reduce the obviousness of this effect. As "little" as a 2 to 3dB difference can make quite a, well difference.

I'm thinking that if the speakers were 0.5 1.5 or 2.5 x the wavelength of 50/60hz apart, then the omni-directional bass wave from each stack would be out of phase with the other stack, as it passed it.

Except that these frequencies are more or less omni-directional...

this sideways cancellation alley could be aimed at the nearest village...

I doubt you could be that effective. You could try the "new" cardiod subs that are finding popularity - they cancel the rear-directed sound waves like a cardiod mic works. Meyer's M3D Sub is one example of this.

...I've just lost a very good job to a competitor, as i wasn't prepared to do a '6 stack noise cancellation system'

And the other contractor was able to provide evidence this works, or was it more of a promote...?
I hate to think this cost you a gig...

...I've looked after multi stack systems before, & i promised myself i'd never do it again!

Explain this...?

oldmics here, has oodles more miles than I do and might pitch-up with some replies, but I warn you - he and I have gone around about this a few years back and his answer will be problematic in itself! This is a difficult acoustic problem.

As well, you could wander over to the forum at ProSound web - they should have a bunch of ideas (and good questions... ) to maybe sort you out.

It "sounds" like you are using "old school" cabinets which are prone to this problem. You need to know the dispersion of your cabinets and minimize their acoustic overlap as much as is practical and possible. The ear is most sensitive to this in the mid- to high-frequencies.

Still on topic, a GREAT example of a terrific sounding "conventional" (non line array) cabinet that largely moots this problem is the L-Acoustics ARCS, which have a very narrow 22.5° dispersion - they make a wonderful sounding array. A double-stack (180° horizontal dispersion, ±40° vertical dispersion) is shown just below...

[JBL 4645]

boputnam

I’ve noticed this affect with the arrays of JBL control 1 placed on the sidewalls with two sets spaced out tends to create when facing them with (pink noise) and just moving from side to side kinder leaning one way and then the other way hence (comb filtering).

A whooshing sound is created this would be considerable less if I installed a third JBL Control 1 as making the gap less and lesser.

I wouldn’t trade back to bipolar or dipolar all I have to do is work the problem and solve it with some additional amplification and digital technology.

Bingo I guess when listening to and please hear me out. The THX home system circuitry creates a difference on the right out-put side with a decorrelation device that separates the monaural difference between the two surround loudspeakers with a hand-sawing effect when turn the THX off you’ll just hear a steady pink noise when activating it you get a hand-sawing effect thus creating a wider spacious sound.

I guess digital technologies will solve multitude problems like the one Jody is describing here.

[boputnam]

Also, if you can adjust the gain of each sub "stack", lower the gain of one side and you will reduce the obviousness of this effect. As "little" as a 2 to 3dB difference can make quite a, well difference...

To your ears, this has much the same effect as a physical repositioning (and is hella easier!).

I've recently read a great article on this - with some very compelling polar plots to boot. It was either on the L-Acoustics or Meyer's site. I'll try and re-find it and post some detail...

[Oldmics]

Jody

Can we get some additional information about exactly the system is that you are using for your events?

Specific number of boxs that you are using per side and what they are loaded with.

Your comment about power alley can be interpeted in a coupla different ways.

Most guys refer to power alley in the low frequency aspect where the summation of low frequenecy energy information is the greatest.

After rereading your post it appears to me that you are refering to the whole audioable frequency spectrum that your system is producing.

Could you tell me what the problem areas are that you would like to address?Is it just the low freq?

Oldmics

[Jody]

yes, sorry, should have explained it better.

The system is a horizontal array, with 2 stacks, to recreate the stereo signal as accurately as possible, and everything sounds great on the dance floor, especially in the middle where the bass summs. Now the main part of the question is to do with noise pollution in a village. the polluting frequencies are, i would guess, mostly around 50 / 60Hz.
If the village was in line with the 'power alley', that would obviously be bad.
Now imagine the village at 90 deg to the power alley, ie off to the side of the sound system, then imagine a 60hz pulse from the 2 stacks, placed 9m apart from eachother. as bass at that frequency is pretty omni directional, so imagine a wave (60Hz = 6m approx) from the farthest stack passing the nearest stack 180deg out of phaze (6m + 3m = 1 1/2 wavelength), therefore cancelling, and not annoying the village.
Obviously there is many more frequencies and different radius-of-waves involved, but to drop an anti phase bomb at 60Hz would surely help, no?
Would this work?
Would this also work with stacks at 15m, or 21m (6+6+3, 6+6+6+3)?

There must be other comb filter effects with different distances between stacks, but how to work them out? draw hundreds of circles? Its not really an issue with the top boxes, as they are playing stereo stuff,
Obviously, it would be better on the dance floor with a central mono bass, but flying top boxes isn't always possible.

But then what if a large central bass speaker is added? Did this once at a festival in spain, and there were 2 cancellation alleys at roughly 45 deg on each side.
not unpleasant though, there was a lot of bass, so you could choose if you wanted to dance in a loud bit, or a quiet bit.


These are the tops.


Tad4001 & a new PHL cone
Bass is a trapezoid 2 x 18 reflex with a discontinued (the fools!) beyma copy of a discontinued jbl cone, the g400
All analogue time allignment and crossover filters, minimal analogue parametrics, opus amplifers, Allen & heath V6 mixer, no graphics, proper cables, minimum interconnects.
there's a group of us with the same type of system, and we work together on bigger gigs to make things like this.




i am aware of the meyer box, but this is more to cancel rearwards soundwaves, no? question is more to do with inter reactions of 2 sources at specific frequencies.

The multi stack system i worked on was huge, and with 6 stacks all facing in. In the middle it sounds great, anywhere else, it sounded like a train crash. this sort of thing can work in a small space creating a sort of 'loud' effect, due to the slight time delays, appreciated by some dance styles, but it absolutely does not work large scale.
The 'competitor' (much larger, and very good product range, but not hi-fi) who got our stage this year is another manufacturer affiliated system, who have developed a 'noise cancellation field' where the 6 stacks supposedly create a constant sound field inside the 'zone', and yet outside the area, the polluting frequencies cancel out. This is probably true, and no doubt they've done all the tests, printed the graphs and persuaded the license issuing authorities and festival organisers what a great thing it is. However, it does NOT create a constant sound field (when done large) it sounds like a train crash. No delaying can fix this. it could for a fixed point, but only to make it worse somewhere else.
I'm wound up because our tent was not the cause of any of the sound problems last year. I find reflex to be of a far superior sound quality, better frequency range and to have less range than horn loaded, annoying less neighbours, but the license now says that 'noise cancellation' must be used on all main stages. So, thats what sparked all this off, trying to work out if theres a way to noise cancel the neibours without destroying the stereo reproduction. Too late now, for this year, but an interesting subject to learn more about (for me)

I could have gone on pro sound forum, or a number of others, but i find them full of know-it-alls who think digi controllers sound good. in terms of progressing through a/b tests, i'm way ahead of them. too many people who know so much running shit sound systems. (oops, i probably just offended a load of people!). anyway, a different sort of problem for you all

"anyone hear a good dj system recently?" i rest my case

i'm on a crusade to bring some high fidelity to large systems here, but its an uphill struggle.

[boputnam]

yes, sorry, should have explained it better.

Many make that mistake - not a problem...

The cabinets looks beautiful - thoughtfully designed.

Tad4001 & a new PHL cone

I love the TAD, but can you tell us about the horn? What are the dispersion characteristics?

i am aware of the meyer box, but this is more to cancel rearwards soundwaves, no? question is more to do with inter reactions of 2 sources at specific frequencies.

Yes, and a cardiod approach would help with this because some ±40% (guessing on this...) of the bass response is cancelled, which can only help with controlling undesirable "spill"/coupling.

The 'competitor' (much larger, and very good product range, but not hi-fi) who got our stage this year is another manufacturer affiliated system, who have developed a 'noise cancellation field' where the 6 stacks supposedly create a constant sound field inside the 'zone', and yet outside the area, the polluting frequencies cancel out.

I have not been impressed with these actually working as described. Oldmics knows more than I, so maybe...?

I'm wound up because our tent was not the cause of any of the sound problems last year. I find reflex to be of a far superior sound quality, better frequency range and to have less range than horn loaded, annoying less neighbours...

Absolutely agree on that. My love of line arrays is severly hampered by my experiences of them run by other soundguys...

I could have gone on pro sound forum, or a number of others, but i find them full of know-it-alls who think digi controllers sound good. in terms of progressing through a/b tests, i'm way ahead of them. too many people who know so much running shit sound systems. (oops, i probably just offended a load of people!)...

I share your disappointment - the place is rife with users of mid-tier gear (at best...) but who are emotional about their impressions. That said, there are a few really good guys there, but they "stop by" less frequently as the site has grown in popularity...

[boputnam]

Obviously there is many more frequencies and different radius-of-waves involved, but to drop an anti phase bomb at 60Hz would surely help, no?

But, the rest of your post has me thinking...

...minimal analogue parametrics

and...

...no graphics

Have you tried some extreme notch filters at the resonant frequency? Whacking -18dB (or more...) at hi-Q from your L/R mix might do wonders. I'd not be afraid to try this.

That said, have you modelled the acoustic response of those mains? I'm guessing a good set of PEQ presets based upon your "normal" configuration would go a long-ways to remedying some of your response symptoms.

[Zilch]

I know you said no DSP, but there's some approaches like "steering" here which may be applicable:

http://www.jblpro.com/pub/technote/fat_wht.pdf

http://www.jblpro.com/pages/install/...ss%20Array.pdf

The Meyer tech notes are too though for me to fathom, typically.

[Berkeley.... ]

[Jody]

I love the TAD, but can you tell us about the horn? What are the dispersion characteristics?

roughly 60/60, and sort of a cross between tratrix & exponential, i believe. we make them ourselves, and they were designed almost entirely based on listening tests. very minimal squishing of the sound waves (compared to many pa horns, any way).
they are not (unfortunately) carved out of a single lump of greater mongolian sapient pearwood.... yet!
i'm open to suggestions on wood horns, not my forte.

note the edges that are causing edge diffraction (other post). i'm about to build a test box with flat front & rounded edges, with a more hi fi style grill, or no grill, just a clip on front lid for transportation, so i may end up ripping them apart, and removing the grill supports alltogether. thoughts?

[Jody]

Have you tried some extreme notch filters at the resonant frequency? Whacking -18dB (or more...) at hi-Q from your L/R mix might do wonders. I'd not be afraid to try this.

these are all good ideas, but there is a kind of 'out-of-the-box' effect, where the music is all around you, as a pose to coming out of a box (or sounding like its coming from another room in really bad cases) which gets trashed when any equalisers are plugged in line. It could be inserted after the electronic crossover, so only affecting the bass, but from experience, this makes it sound all disjointed.
obviously a bit of a mission to have some control over noise pollution, without ANY degradation of the music on the dance floor.

Some of the things people have been saying on various forums about some of the partys we've done.:

Omni 2004 , "the dance floor energy was fantastic. This was helped by the amazing bass and clarity of the Opus sound system"
"and finally...the sound system guys in the front room...what a rig!!!!!...absolute clarity across the whole bandwidth

the sound made me trip.........and i was "straight" all night so know what i'm talking about!!!

thought I'd be taking an early bath after the transient night friday
No chance! there was no escaping the fat tunes and the opus rig - ooh yeah

I thought the whole place looked stunning and the sound was phenomenal (even more so when Plank turned it up for my last tune hehehe)

thankyou for a lovely party people, very much enjoyed doing the chillout visuals and meeting all you lovely folk, espesh Steve Ishwara,Mark insideusall,dave arci,oo - emma-oo.Et & Sarah.Ivy & Diane and the lovely lady with the fluffy dog who brought the splendid mainroom system.Phew! & a fucking good dance was had by all!

that soundsystem was just mental
What can I say ? That was a fucking wicked party.

Great great party! very releaved to hear that kick ass sound system!
yes indeed!
phat!


very well organised. got impressed with the sound quality! opus in a squat! well done mindscapes!

Is it just me, or was Beirdy's set some kind of twisted enlightment ceremony that made the party unforgettable? Oh well.... Even a techno head from Detroit agreed. He didn't want to DJ in the acid house room, in front of 1 and a 1/2 people.
Phhhhhhhhhhhhhhhhhhaaaaaaaaaaaaaaaaaaat!


7am onwards in the main room had me stomping my feet and wiggling my bottom until beardy finished at 1pm. What a boogie that was. AMAZING tunes flying out of those speakers, and by then there was room to dance.

Chrysalid.
Oh and the soundsystem was the best I've heard bar none. I don't understand how a huge club like SE1 has a soundsystem thats quite muddy and distorted yet a much smaller more intimate venue can come up with something that sounds so crisp and clean.

Being a *future-girl* this party was just spot on....the sound in the main room was amazing....beautiful...it felt like my ears were being caressed (all night....mmm!).......smooth, full and crystal clear.....I think its fair to say I was in *Sound Heaven*.....

you get the drift.

[boputnam]

...roughly 60/60, and sort of a cross between tratrix & exponential, i believe.

That is a lot of dispersion from each horn. 60° horizontal will have a great deal of overlap even in your arc'd array (post #7) - I guessing about 30° overlap, each side...? Difficult. Broad dispersion is desirable when using one cabinet, but problematic when arraying.

...we make them ourselves, and they were designed almost entirely based on listening tests.

That is a problem - there are all manner of unintended characteristics that may not be easily or reproducibly detectable by ear in "listening" tests. Certainly there would be almost nothing relevant gained from listening to one, versus deploying arrayed multiples. I've experienced this first-hand with a friends BagEnd "Crystal-R" mains. Alone they measure and sound great; arrayed in almost any splay they have horrid comb filtering effects. Not pleasing at all.

these are all good ideas, but there is a kind of 'out-of-the-box' effect, where the music is all around you, as a pose to coming out of a box (or sounding like its coming from another room in really bad cases) which gets trashed when any equalisers are plugged in line.

You are beginning to sound like those you distain on the other sound forums...

Provided your choice of electronics is high-quality, the sound should not / will not get "trashed" when EQ's are in the signal path. As example, good GEQ's are out of the signal path when faders are at Unity; PEQ's have I/O switches on each bandpass and are incredibly good sounding (the Meyer CP-10 for example).

It could be inserted after the electronic crossover, so only affecting the bass, but from experience, this makes it sound all disjointed.

That would be a phasing/time alignment issue.

I guess I can't offer more suggestions without a better understanding of the frequency response of each cabinet alone, and what they do in multiples arrayed, and what their impulse response looks like. I am left with the impression you are running these mostly "as is" without much-if-any EQ, either to tame cabinet resonance or environment response, and without any time-alignment - that is a recipe for failure in a large system.

From the reviews you shared you may be doing better than some competitors, but I've been to plenty of shows where the crowd was raving and I was crying. The Prince show at the Rio is being done terribly, as example. I saw their Smaart which confirmed what my ears told me and is not a curve I would ever intentionally go with - but the crowd/soundguy wanted "bump" and they got "BUMP". Likewise, the flown line-arrays were driven at ++115dB and were damned hurtful in A-weighted SPL curve. But, the crowd rocked. I know it would have been a better show at 95-100dB, flat response leaving much improved intelligibility and gain structure.

I guess what I'm saying is, crowd response is one thing - they can have fun even when the sound is not the best - but they've too often gotten USED to bad sound! You are not happy with your sound. However, lacking a non-subjective understanding of what your system is producing, you are at a disadvantage to remedy it.

[Oldmics]

Jody

The system that you are trying to control the low freq information as to accomidate the nearby town,consists of how many low end (double 18 )boxs per side?

While I understand your personal hesitation to institute any digital speaker management system because of inferior sound quality,it will be pretty much impossible to steer a small system (only 2 double 18 boxs per side) or by trying to steer a system using analogue processing.

While I prefer analogue processing for my hi-fi listening pleasure,the wide tolerences of analogue preformance compared to exacting digital processing is the only way to get the large sound systems to sound as good as they do.

Its not impossible to do so in analogue,just much more difficult and not as exacting unless you have some serious measurement tools and skills.

The large system depicted in your virtual picture shows speakers only on one side of the room.Is this correct?
A system of that size could be directed in the low freq realm from about 500 hz down.

We really need to understand the exact system layout that you are attempting to control.
Just adding one box into the systems equasion creates a different problem to deal with.

Digital processing allows for very sophistcated parameter control.This incrementaly small,exacting time adjustment type of control is the easiest way to do the steering of the low frequency information.

Even with the proper tools a measurement plan has to be formulated.

Setup considerations such as distance between stacks,distance from complaining neighbors,quanity of sub enclosures all have to be graphed out for calculation.

While I have never done system steering for the reasons that you need to do it for,I have done it for better audience coverage patterns (shits and giggles) with some interesting positive results.

It takes a lot of low end boxs,lots of individual amps and a lot of digital processing power to execute.

I just don"t think that you can achieve your desired goal (easily and within a reasonable time frame) without the digital gizmos.

I am addressing only your original problem of the low frequency.

I"ll stay away from any discussion on the horror of comb filtering in multiple horizontal array boxs of spherical radiating enclosures.

Only TurboSound believes they can accomplish this feat with trap boxs.

We will try to guide you in your quest.Give us some information more to go on.

Bo,your correct!The more answers that I offer the more problems that crop up.Whats with that !!!!

Oldmics

[Jody]

http://www.jblpro.com/pages/install/...ss%20Array.pdf



[Berkeley.... ]

on this one, i don't quite get how they're set up.
3 speakers hanging from ceiling, ok. facing down?
is this in addition to a main pa, or is this the main bass for the system?