Creating a sub array with 4x 18" sub cabinets

[DanSteely]

We have an installed school stage PA consisting of 4x 15'+2' top boxes truss flown, 2 on the left, 2 on the right. Built-in under the 1m stage we have 4x 18" subs 2 on the left, 2 on the right.

Each box is driven by a single channel of a Behringer EP2500. The controller/crossover is a Behringer DCX2496 we use 2 inputs and 4 outputs and the crossover frequency is 110Hz.

What I'd now like to try and do is minimise the bass on the stage and maximise it in the auditorium and could use the spare outputs on the controller to separately control each sub cabinet in a kind of pseudo cardioid array.

So I have the ability to do things like point 2 of the four SB cabinets away from the auditorium (and into the understage void), delay & phase reverse the outputs in the controller etc.

The cabinets are StudioSpares Auditorium range (first gen) so are not of the highest quality..

So my questions are:

Will it work & Is it worth the bother?

Assuming two subs are facing forward & two are facing backward in this setup, how should I start calculating my delay & phase settings for my controller?

Any thoughts would be most welcome...

[paulears]

Those boxes are actually quite nice sounding, well built - and good performers, so I'd not worry too much about what comes out of them. I'm not certain that anything you do with them will help bass levels on stage if you work them into the void, as unless the stage to void barrier (the floor) is amazingly dense and isolated. Most stage floors are pretty basic in construction, so your idea to create a cardioid sub output into the room might fail because the floor itself will resonate upwards.

[jameskerr87]

You will find a little less power out front, but try it and see if its worth it.

 

Correct me if im wrong but the delay should be calculated as the distance between the front of the bins, and phase reversed

 

 

There is always room for improvement with sub configurations

[darkelf151]

If you have a poke about on Das's website, they had a pdf on how to setup cardioid sub arrays using smaart etc - definitely worth a read through....

 

Here would be a good starting point...

[Brian]

...Built-in under the 1m stage we have 4x 18" subs 2 on the left, 2 on the right....point 2 of the four SB cabinets away from the auditorium (and into the understage void)...

I'm by no means an expert on Cardioid Arrays but doesn't the sound have to be able to couple freely between the forward facing and rear facing speakers? As described, it sound like you've got your speakers sat in the open face of a sealed five-sided box. Any rear-facing speakers are going to see the under-stage void as a resonant chamber and interact with it accordingly. You'll be creating some sort of double-chamber bandpass arrangement with some very odd characteristics.

 

To my eye it looks like a few sheets of 25mm ply to seal off the void just behind the subs is what you need.

[Bobbsy]

Just for fun I'd have a poke around Dave Rat's blog(s). If you don't know the name, he runs a California sound company and also tours doing FOH with bands like the Red Hot Chilli Peppers, Blink 182 and tons of others.

 

Over the past few years he's done a lot of playing with various sub layouts. Not all could be appropriate to you (he has access to millions of dollars in equipment) but some layouts use exactly four subs.

 

Even if you don't end up using any of his ideas, you'll certainly learn a lot.

 

Unfortunately, you'll have to do a lot of skimming since he sticks a sub-related entry in every so often without warning. Even so, the whole blog is a good read.

 

Original blog is HERE.

 

Then a year or so back he moved HERE.

[Mark Payne]

Here is the basic recipe for end fire CSA

 

Lets assume we want to deal with the octave centered around 60Hz.

Wave length at 60hz = 5.6M ish

We are interested in 1/4 wavelength = 1.4M

 

So you place your back sub 1.4M behind it's mate in front (pointing forward in the normal way)

Then you delay the one in front by 4.2ms to time align it back the the back sub (this is time zero).

 

The punter in front of the PA hears two cabinets that have been time aligned.

The punter behind the PA hears the rear sub at time zero and the front sub 1.4M (4.2ms)late (relative) because of the delay and another 1.4M (4.2ms)late becuase of position.

 

Hey presto... total delay = 2.8M (8.4ms) and that is half wavelength ... and that is people is half wave cancellation.

 

Job done. End Fire.

 

M

[DanSteely]

Hi Mark,

 

Just the job!! Will try this out soon and report back..

 

Many thanks.

 

Dan

[Mark Payne]

Hi Mark,

 

Just the job!! Will try this out soon and report back..

 

Many thanks.

 

Dan

 

You are welcome. Let me know how that goes.

 

The trick is the realisation that delaying a source does not fix it in a different place.

It makes the delayed source track a circle, radius of the delay distance, centred on the actual physical location and diametrically opposite from the viewpoint of the listener.

 

Cheers

 

Mark