How To......Cardioid Sub Arrays

reduce the sub on the stage mainly. but i suppose knowledge on both would be useful. :)

Edited by Ohmen Audio - 12 August 2013 at 7:23pm

After reading this thread i have learned alot about the cardioid sub set ups but i am having great difficulty in figuring how i would apply this to my system in an effective manner considering i am running hogg scoops and 1850's. would i have to have a stack of just 1850's or hoggs or just a certain amount of each. say 1 hogg at the bottom led on its side with one 1850 on top facing forwards and and other 1850 facing backwards would this be applicable?? please excuse my lack of understanding if this seems to be a silly question but if someone could maybe build on this and lend a hand i would greatly appreciate it.

Hi,

I'm running a small (500 cap) outdoor event on the weekend of 30th Aug - 1st Sept and am looking for someone with good experience of Cardioid arrays either to do a days paid work as a consultant to help setup up cardioid subs in 3 (very small 100 cap) tents or would be interested if anyone with cardioid experience was willing to do (fairly cheap) sound hire for one of the 3 tents in addition to helping with the setup of all tents. Obviously will have crew on hand - this is more an advisory / technical role due to noise restrictions from the council.

The event is 1 hr drive NW of London - please PM me if you have relevant experience and would be interested in helping out - or know of anyone who would.

Cheers!

Here`s a little piece I wrote today about fun with the world of Cardioid! Apologies to Kevin if I`m repeating some of his stuff!

Weird World of Cardioid Subs





Firstly this isn`t some new thing to somehow gain a better sub sound. This is just ways to keep the sub sound you have in the right places. It was born out of one festival where the noise limits were frightening but only to the sides of the stage. There was a block of flats about 70m away from Stage left and a known "complainer"!. And it really only works if you have all the same type of sub with the same type of driver! And if you want to try it with scoops and " W" bins together...good luck & let me know how you get along!
So here`s how we worked out the mad set-up, first the maths! In dry air at 20 °C (68 °F), the speed of sound is 343 meters per second. The centre of our cardioid freq is at 60hz ( this is the freq we want to create the most rear or side rejection at) it can be any freq within the bandpass for that particular box.
There`s a few ways to get a rearward rejection,:
1)     Turn one box in an array around , flip the phase and apply a delay equal to the distance between forward and rear facing drivers, usually you can simply measure the width of the box if you have front loaded subs and apply that delay in mm ( or ms). For horn loaded subs you have to account for the horn path but again if you are using the same type of box ( hopefully!) in your array it`ll always be the distance between the front and back edges of the boxes.
2)     Space the boxes 1/4 wavelength apart (90 degrees apart). Now delay the front box another 1/4 wavelength (90 degrees). The output from the front box takes 1/4 wavelength to reach the rear box, and another 1/4 wavelength you added artificially, so cancellation ensues. The undelayed sound from the rear box takes 1/4 wavelength to get to the front box, so it sums in phase out front.

There are other configurations that use the same principles: a rearward delay to a tombstone etc etc. But we stuck to the two that others seemed to have the best results with

So to work out what 1/4 wavelength is to space the boxes …343/60/4 (Speed of Sound / centre frequency/ 4) = 1.429 m .
And to work out the delay time 1000/60/4 = 4.17 (Period (ms) = 1000 / Frequency)
Keep in mind the speed of sound changes with temperature so that 343m value will change and so the delays and spacings will change. This can be quite a lot over a 5 degree change in temp. I just go for what I think the temp will be during the event. Outdoors get a forecast …indoors have a guess at how hot & sweaty it`s gonna get!

What we did next was to try a few different configs to see what worked best. Excuse the crappy fone fotos…I need a new fone desperately! We only had 4 subs out as we didn`t want to piss the neighbours off too much with constant freq sweeps all day long at a reasonable level. So we laid out a circle and measured at 15 degree intervals around the arrays from front ( 0 degrees) to rear (180 degrees)and swept from 20hz to 200hz at each point. Highly dull and needs two people ( one to walk the mic around the yard and another to shout" ready" about a million times- never knew sound was so much fun!)

First is a straight stack of 3 subs with one inverted

Plot ......http://img22.imageshack.us/img22/8282/3xvsb218normal.jpg

The plot shows the standard box as a dotted line at different freqs and the colours correspond to the same freq with the hard line being the interted box measurements. The measurement is 180 degrees around the box so the front of the box is at 0 degrees at the right and the rear is to the left. Db is measured from the centre outwards...further out the louder it was! It`s quite tricky to read what`s going on as the traces all overlap etc etc but we were looking for an overall trend at all freqs. Notice the lump in standard ( dotted line) 30hz @ 30 degrees this is probably down to the ports on the NCA subs being on the outside and it picking up the phase changes at the measured distance 10m. Not a great amount of rear cancellation in fact quite a rag tag response.

In reality we were getting rear rejection but the nature of frontloaded boxes means that just by inverting one box we weren`t getting enough rejection at the rear ( or more especially the sides!)

Then a 2 x 2 Tombstone



Plot.....http://img22.imageshack.us/img22/4733/22vsb218.jpg

Ver similiar to a standard 3 high stack...? Sounded like we were getting a bit of rejection at 60 and 120 degrees but not much rear rejection.

Then 2 + 1 + 1 - Tombstone



Plot...http://img22.imageshack.us/img22/7830/211delayedvsb218.jpg

Starting to see a side rejection....

Finally 2 + 1 + 1 ( 1 inverted)



Plot...http://img9.imageshack.us/img9/4323/21reversed11vsb218plot.jpg

This is now a comination of Tombstoning and reversing a box.
Well that seems to work! We`ve not lost any forward gain and between 60 and 120 degrees we`ve got a good 7-10db gain reduction on all 3 measured freqs. Only problem is we are now getting processor hungry! We need 3 different delays on top of our standard set-up.

So after deciding that a combination of both methods was for us Reay knocked up this little CAD for us to see how mad it looked before the gig!



The only difference on the day was to keep the two inverted boxes on the floor. I don`t like subs firing into each other directly and if it was with hornloaded boxes I would definitly try to keep the boxes from firing directly at each other. It sounded great out front no weirdness with the kick drum and with the two infill stacks covered right across the stage evenly. As you walked off to 40 degrees it started noticably tailing off. At 70 - 110 it was hard to tell if it was on! It didn`t reject at the rear the same as a standard one inverted box array but was still down on the usual standard 4 x 4 sub array.



I`ve picked all of this info up from the net. Mostly from PSW/ SPlans etc etc and am reading Dave Rat`s blog about his Vortex and Slotfire systems with great interest. It is a real world solution to getting sub in the right place ( as long as you have the room to start laying subs out!) . Rog`s article on bass arrays goes into this kind of arrangements in great detail and you can sim up different arrays with Mapp online. But I am always sceptical of how the actual array sounds. The fact you are introducing phase changes (delays) means that even though an array can sim up fantastically it could sound very strange! I have tried a few different set-ups on Carnival floats in an attempt to get more rearward sub ; some have worked, others haven`t. Not because the maths is wrong just the fact that it didn`t sound " right" !

Disclaimer...this is only a rough guide and wasn`t done to exacting standards ( there was a massive chiller unit next to us going on & off which probably was why the 30hz readings were all over the place!). It was a fun afternoon in the sun with some boxes and a few beers!


And maybe next time.....



But that`s another story....


.p.

Edited by Phil B - 15 August 2009 at 8:28pm

Having done extensive measurements on the style of Cardioid array mentioned here, and CSA, and various other types, they all work differently.  They don't all do the same thing.

The simple array spoken about above will potentially give you more output at the front and less at the back,  the CSA gives you significantly less at 180degrees (directly behind) but also less out front.


It's not JUST about 0 degrees and 180 degrees.  It's often about 90 270 304  201  and every other angle from the cabinet.

For me CSA just doesn't work right in alot of situations.  The cardioid array above can do. though you do need distance from the rear wall.



Rob

roborg wrote: For sub-bass control i'm not convinced there is any advantage over just pointing all the subs forward & forming a wide horizontal array, in most circumstances.  IE try to induce as much diffraction directivity as possible & then the radiation pattern tends to be cardioid shaped anyway.

While it is true that a large horizontal line of speakers will have significant directivity, it seems to create more of a figure of 8 pattern than a cardioid. You can see it in Rog's bass guide, page 2, where even just a row of 4 subs has a significant figure of 8 shape and there is still a lot of bass directed backwards onto the stage.

Our cardioid array on the other hand, even with just the same 4 subs set up in two rows of 2
you would get something much more like what is shown on Rog's guide page 14. Obviously reflections and real life would mean that it wasnt as perfect as is shown here, but would still be a significant, and often scary, improvement in the amount of bass traveling back onto the stage.

But yeah totally agree, i'd really love a big pile of subs in a field and plenty of time to play about with this all and really get my head around it properly, at the moment its all theory in my head and i've not had very many chances to actually put it into practice.

jamwa wrote: or if you use DB you can just point a thrid of your subs 180 degrees the other way run these on seperate amps and switch the CSA mode on - simples!!!!

LOL, yeah DB sub users have it easy     LOL, well for other users, even though we dont have DB's fancy processing and i'm sure staggered delay times to extend the bandwidth, this technique will also work to an extent. If you have relitivly deep subs then reversing one of a stack of 3 is going to move their acoustic sources back a fair bit of physical distance anyway. It probably wont be the proper 1/4 wavalength back and so wouldn't be as effective as having a seperate second row of subs, but in cases where you are really pushed for space if you play with the processing and delay times to make it all match up and cancel properly i'm sure you may get some fairly acceptable results. In most cases anyway there is no real need to cancel ALL of the sub energy going back to the stage just reducing it by a significant amount would be a big help.


k